JP2002025809A - Iron-rhodium alloy magnetic powder, its manufacturing method, magnetic recording medium and recording reproducing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide iron-rhodium alloy powder which can be made suitable for security use by taking advantage of its intrinsic magnetic properties, such as temperature-dependent properties and a medium formed of the same. SOLUTION: A magnetic medium is formed of an iron-rhodium alloy powder, in which at least iron and rhodium serve as component elements. The magnetic medium is turned from an antiferromagnetic to a ferromagnetic material through magnetic transition due to heating, increased in saturation magnetization volume, and kept ferromagnetic even if it returns to room temperature. The magnetic medium is heated by the use of a device that has a function of generating heat, by which the magnetic medium is changed in saturated magnetization volume so as to record data, and the data are reproduced by the use of a magnetic head that reads out a change in the saturation magnetization volume.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic powder containing at least iron and rhodium as constituent elements, a magnetic recording medium utilizing the temperature dependence of the unique magnetic properties of the magnetic powder, and a magnetic recording medium utilizing the unique magnetic properties. The present invention relates to a recording / reproducing method using temperature dependency.

[0002]

2. Description of the Related Art A magnetic recording medium records and reproduces information using a magnetic head. For this recorded information, for example, in the case of digital recording, the direction of magnetization is assigned to 0 and 1, and significant data is created by the combination of 0 and 1. Therefore, the information recorded by the magnetic head has no meaning as it is, and becomes significant data only after signal processing and conversion into analog information.

For example, when recording image information, a signal digitally recorded by the combination of 0 and 1 is subjected to signal processing by a microprocessor or the like in accordance with rules set in the system, and converted into image information. Then, by displaying the information on a display or the like, the content can be visually discriminated for the first time, and the information becomes significant information.

On the other hand, information recorded on a magnetic recording medium is
In order to obtain information that can be directly discriminated by visual observation, a method is known in which a heat-sensitive printing layer is further provided on the magnetic recording layer, and character information and patterns are printed and recorded on the heat-sensitive printing layer using a printing thermal head or the like. . This method is widely used in prepaid cards, for example, for printing and recording the amount of money used each time the card is used. in this way,
The recording element is an element having a heating function, and has a completely different function from a magnetic head used when recording a signal on a magnetic recording medium.

Therefore, the method for magnetic recording and the method for printing and recording use completely different elements and principles.

It is known in the literature that an iron-rhodium alloy undergoes a magnetic transition from an antiferromagnetic material to a ferromagnetic material at about 150 ° C., thereby rapidly increasing the saturation magnetization.
The present inventors have paid attention to this unique magnetic property. That is, it was considered that the above-described magnetic recording and print recording could be simultaneously realized by utilizing the temperature dependence of the unique saturation magnetization.

Further, such magnetic characteristics suggest that there is a possibility that the present invention can be applied not only to the above-described magnetic recording medium but also to various devices such as a temperature sensor.

The present inventors have considered that it is essential to develop the iron-rhodium alloy into fine particles of the iron-rhodium alloy after developing it into such devices as magnetic recording media and sensors. Since fine particles can be made into magnetic ink, a magnetic film can be formed on various substrates with an arbitrary thickness, shape, and area, and a molded article having a complicated shape can be obtained. Therefore, the present inventors thought that the key to the practical use of the iron-rhodium alloy as a device such as a magnetic recording medium or a sensor depends on whether the alloy can be made into fine particles.

On the other hand, as a method for producing an iron-rhodium alloy, only a method for producing a bulk material by a metallurgical method and a method for producing a thin film by a sputtering method are known. Also, regarding these production methods, the number of reported documents is extremely small. According to these documents,
It is reported that composition control of both bulk materials and thin films is extremely difficult. Therefore, the iron-rhodium alloy itself has not yet been clarified in detail, and at present, there is no known technique relating to micronization.

[0010] As described above, iron-rhodium alloy is an unknown material from an academic point of view, and therefore, there has been no research aimed at its practical use.

[0011]

DISCLOSURE OF THE INVENTION The present invention has been made in the state where there is almost no knowledge to be referred to, and has succeeded in making fine particles of iron-rhodium alloy powder. An object of the present invention is to provide a magnetic recording medium completely different from a conventional magnetic recording medium and a recording / reproducing method thereof by utilizing the temperature dependence of the unique magnetic properties of the magnetic powder.

[0012]

Means for Solving the Problems The present inventors started by searching for a material and a manufacturing method suitable for fine particle synthesis.

As a basic process, the present inventors first prepared a precipitate containing iron and rhodium by mixing an aqueous solution containing iron and rhodium ions and an aqueous alkaline solution. Next, this precipitate was reduced by heating to obtain an iron-rhodium alloy magnetic powder. At this time, the iron-rhodium alloy magnetic powder
An iron-rhodium alloy magnetic powder containing at least iron and rhodium as constituent elements, wherein the iron-rhodium alloy component is Fe
When represented by _1-x Rh _x , an iron-rhodium-based alloy magnetic powder was prepared in which x was 0.4 or more and less than 0.8 and the particle size was in the range of 20 nm or more and less than 200 μm.

Further, the present inventor has also conducted research and development on a method of manufacturing a magnetic medium using the iron-rhodium alloy magnetic powder, and has studied in detail the magnetic characteristics of the magnetic recording medium.

As a result, it has been found that the use of the above-mentioned constitution of the magnetic powder shows a very unique temperature dependence of magnetic properties which cannot be found in a conventional magnetic recording medium. Furthermore, they have found that the use of this peculiar temperature dependency can provide a magnetic recording medium having extremely unique characteristics, which cannot be realized with a conventional magnetic recording medium, and have accomplished the present invention. Further, the present invention also provides a recording / reproducing method utilizing the temperature dependence of this unique magnetic property.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail below.

The basic properties of an iron-rhodium alloy are as follows:
It is described in "Physics of Ferromagnetic Materials" (by Toshinobu Chikaku, Shokabo). According to this, the iron-rhodium alloy is about 3
At 00K, the saturation magnetization changes sharply with the temperature change and shows a slight temperature hysteresis, but the saturation magnetization shows almost the same temperature dependence in the temperature rising process and the temperature decreasing process.

Regarding the manufacturing method, there is a literature examining the manufacturing method and magnetic properties of an iron-rhodium alloy ingot (J. Appl. Phys. 35, 938, 1964, J. Appl.
hys. 37, 1257, 1966). According to these documents, in order to obtain an iron-rhodium alloy, it is necessary to melt an ingot, heat it at a high temperature, and then rapidly cool it.

The steep change of the saturation magnetization of an iron-rhodium alloy with temperature is a very interesting phenomenon in practical use. However, even if the molten ingot, which is known as a method for manufacturing an iron-rhodium alloy, is manufactured by a method of quenching, since the iron-rhodium alloy is in a lump state, the present inventors believe that only limited applications can be developed. Thought.

In particular, in order to develop a magnetic recording medium or various sensors, it is indispensable to form fine particles. However, regarding the magnetic powder of the iron-rhodium alloy, neither the synthesis method nor the magnetic properties were known at all, and it was thought that it was not possible to make the iron-rhodium alloy into fine particles to form a magnetic powder. Is the current situation.

The inventors of the present invention have been studying methods for synthesizing various alloy magnetic powders for many years, and have accumulated many years of technology regarding the method for synthesizing magnetic powders. The iron-rhodium magnetic powder was successfully synthesized as a result of various studies on its synthesis method as one of various magnetic powders.

On the other hand, the present inventors have investigated the magnetic properties of the synthesized iron-rhodium alloy-based magnetic powder, and as a result, surprisingly, they have a novel magnetic property completely different from the magnetic properties already known in the literature. I found something. Although details will be described later, in addition to the steep magnetic transition known in the literature,
A temperature hysteresis of a remarkable saturation magnetization was found by making the particles fine. This is considered to be a phenomenon peculiar to fine particles, and is an extremely important characteristic in practical use. As described above, the unique magnetic characteristics that are the basis of the present invention have been found completely by accident.

Further, the present inventors have noticed that using this unique magnetic property, a very unique magnetic recording medium which cannot be realized with a conventional magnetic recording medium can be obtained. It has been reached. As a result of repeated studies on the recording / reproducing method peculiar to the magnetic recording medium, a recording / reproducing method unique to the magnetic recording medium of the present invention, which is completely different from the recording / reproducing method of the conventional magnetic recording medium, was also invented. It is a thing.

In the synthesis method of the present invention, as a basic process, a compound containing at least iron and rhodium as raw materials is dissolved in an aqueous solution, an alkali is added, a precipitate containing these components is obtained, and these are reduced. We developed a process to obtain alloy powder by heating in neutral atmosphere.
Hereinafter, the synthesis method will be described.

(Preparation of Precipitate) At least an iron salt and a rhodium salt are dissolved in water to prepare a solution containing at least iron ions and rhodium ions. At that time, iron nitrate, iron sulfate, iron chloride, iron acetate and the like can be used as iron salts, and rhodium nitrate, rhodium chloride and rhodium acetate can be used as rhodium salts.

The additional elements other than iron and rhodium may include palladium, ruthenium, iridium, platinum, gold, silver, osmium, aluminum, titanium, silicon, boron, rare earth elements and their compounds. These additional elements are effective in adjusting the magnetic transition temperature described later.

An aqueous solution of sodium hydroxide is added to the solution to form a coprecipitate. The coprecipitate is heated, washed with water, filtered and dried to obtain an oxide. Potassium hydroxide may be used as the alkali. Ammonia is particularly preferable as an alkali source because the pH of an aqueous solution in which nitrate or the like is dissolved does not become excessive. The pH value is preferably adjusted to be in the range of 6 to 10 when a suspension of a precipitate is formed by adding an alkali to an aqueous solution of a metal salt.
In an acidic region having a pH of 6 or less or an alkaline region having a pH of 10 or more, hydroxide of rhodium is not easily generated, rhodium is easily removed while being dissolved, and accurate composition control of iron and rhodium becomes difficult.

(Oxidation Step) The above-mentioned precipitate is preferably subjected to a heating oxidation treatment in air to remove in advance the water contained in the precipitate. This heat treatment temperature is 20
The range of 0 ° C. to 500 ° C. is preferable, but omitting this oxidation step does not significantly affect the properties of the final iron-rhodium alloy magnetic powder.

(Reduction Step) The oxide is reduced by heating in a hydrogen stream to produce an iron-rhodium alloy powder. Next, after cooling to room temperature while flowing hydrogen gas, the gas is switched to nitrogen gas and taken out into the air.

The reduction temperature ranges from 300 ° C. to 60
A range of 0 ° C. is preferred. If the temperature is lower than this temperature, particularly iron is not sufficiently reduced, and it is difficult to form a uniform iron-rhodium alloy. If the temperature is too high, the particle size becomes too large due to sintering.

(Heat Treatment Step) In the present invention, the iron-rhodium-based alloy magnetic powder after reducing the oxide may be subjected to a heat treatment in a non-oxidizing atmosphere. The heat treatment conditions differ depending on the target particle size of the iron-rhodium magnetic powder, but the temperature is preferably in the range of 300 ° C to 600 ° C. If the temperature is lower than this, the effect of the heat treatment is hardly obtained, and if it is too high, the particles aggregate due to sintering.

The atmosphere must be an inert gas such as argon or nitrogen or a non-oxidizing atmosphere in a vacuum.
By performing the heat treatment under such conditions, an iron-rhodium alloy magnetic powder having sharper magnetic transition and remarkable temperature hysteresis can be obtained.

This heat treatment is not indispensable, and the desired iron-rhodium alloy magnetic powder can be obtained even if the heat treatment is omitted.

Next, the magnetic characteristics will be described. Iron-rhodium alloys are known to exhibit unique magnetic properties with temperature dependence. That is, at temperatures below about 150 ° C,
Although it shows almost no spontaneous magnetization and the saturation magnetization is almost zero, the saturation magnetization rapidly increases to about 100-130 emu / g in a temperature range of about 150 ° C. to 200 ° C.

The temperature at which the saturation magnetization changes sharply is called the magnetic transition temperature. This is explained because the iron-rhodium alloy exhibits a first-order magnetic phase transition with respect to temperature change, and the low-temperature phase exhibits antiferromagnetism, whereas the high-temperature phase exhibits ferromagnetism. The exact mechanism is still unknown.

When an iron-rhodium alloy that exhibits ferromagnetism due to magnetic transition is cooled to a temperature lower than the magnetic transition temperature, a small amount of hysteresis is exhibited. Becomes zero.

Further, it is known that the magnetic transition temperature varies depending on the alloy composition of iron and rhodium and the addition of the above-mentioned palladium and iridium. The cause of the change in magnetic transition temperature due to the composition of iron and rhodium and additives is known only phenomena,
The mechanism has not yet been elucidated in detail.

As described above, the present inventors have determined that this iron-
With the aim of applying rhodium alloy to magnetic recording media,
We succeeded in making fine powder by working on fine particles.

On the other hand, as will be described in detail later, it has been found that when the magnetic powder is used, a large hysteresis which does not originally appear in the bulk state appears unexpectedly in the temperature dependence of the saturation magnetization. That is, as the temperature increases from room temperature, the saturation magnetization rapidly increases due to magnetic transition in the temperature range of 300 K to 400 K as in the phenomenon known in the literature. Surprisingly, it was found that when the temperature was lowered from the above temperature, the hysteresis was exhibited without following the original curve. Such unique magnetic properties have never been known before,
It has been found for the first time quite accidentally by the present inventors.

The present inventors have been engaged in the research and development of magnetic powders for many years, and have found that when a substance exhibiting such a specific temperature-dependent magnetic characteristic in a bulk state is formed into fine particles, the bulk of the substance is reduced. It may be rarely observed to show magnetic properties different from the state.

The reason is that the surface area is increased by making the particles finer, but the atoms present on the surface have a smaller number of bonding atoms than the internal atoms, so that the distortion of the crystal lattice and the partial rearrangement of the crystal lattice are caused. This is because the like may occur.
Due to such a surface effect, magnetic properties different from those in the bulk state may be exhibited in the state of the fine particles.

It is considered that even in the iron-rhodium-based magnetic powder, due to the surface effect, a large hysteresis which does not originally appear in a bulk state is developed in the temperature dependence of the saturation magnetization.

Focusing on the fact that utilizing the unique temperature dependence of the magnetic characteristics, it is possible to realize a very unique magnetic recording medium that could not be realized with a conventional magnetic recording medium. The effects can be demonstrated, and the present invention has been accomplished.

Hereinafter, the contents of the present invention will be described in more detail. In the present invention, the composition of iron and rhodium was studied first. A magnetic powder was synthesized by changing the value of x when the iron-rhodium alloy component in the iron-rhodium-based alloy magnetic powder was represented by Fe _1-x Rh _x , and the magnetic properties thereof were examined. As a result, when x is 0.4 or more and less than 0.8, the amount of saturation magnetization rapidly increases due to magnetic transition in the temperature range of 40 ° C. to 200 ° C. at the time of temperature rise, and at the time of temperature decrease, It becomes an iron-rhodium-based magnetic powder exhibiting hysteresis following different temperature curves.

It was found that outside this range, only magnetic properties close to those of a mixture of Fe and Rh metals were exhibited. In particular, when x is less than 0.4, there is a saturated magnetization amount based on unreacted ferromagnetic iron, so that even if iron-rhodium-based magnetic powder is generated, it is hidden by the saturation magnetization amount of iron. Sisters,
A sharp change in the amount of saturation magnetization unique to iron-rhodium-based magnetic powder is less likely to be recognized. When x becomes 0.8 or more,
Conversely, since the proportion of unreacted rhodium having no magnetism increases, the saturation magnetization itself decreases.

Next, additional elements other than iron and rhodium were examined. Two types of additive elements were studied: a component that forms a solid solution with iron and rhodium in reduction in a hydrogen stream, and a component that is not reduced in the hydrogen stream and remains in an oxide state.

The solid solution includes iridium, palladium, ruthenium, platinum, gold, silver, osmium and aluminum. The addition of these elements changes the magnetic transition temperature. Among these elements, iridium, palladium, ruthenium, platinum, and osmium are particularly effective in controlling the magnetic transition temperature.

Next, as components that do not form a solid solution, titanium, silicon, boron and rare earths can be cited. These hardly affect the transition temperature, but have the effect of suppressing grain growth during the reduction and the subsequent heat treatment step.
It is effective in controlling the particle size of the magnetic powder.

Further, as described above, the temperature in the reduction step was also examined. As a result, the reduction temperature becomes 3
00-600 degreeC is preferable. Depending on the reduction or heat treatment temperature, the temperature dependence of the magnetic properties, particularly the width of the temperature hysteresis, changes.

When the reduction temperature is lower than 300 ° C., the reduction does not proceed sufficiently, no magnetic transition characteristic of iron-rhodium alloy is observed, and at 600 ° C. or higher, sintering occurs and the width of the temperature hysteresis is small. Become. In general, when the reduction temperature is higher than 600 ° C., the temperature hysteresis of the saturation magnetization decreases as the temperature increases, and finally disappears, and becomes equivalent to the temperature characteristic of the bulk.

Further, after the reduction, a further heat treatment is performed to produce a more uniform iron-rhodium-based alloy magnetic powder. This heat treatment is particularly effective in increasing the hysteresis of the saturation magnetization with respect to the temperature. This heat treatment is preferably performed in a non-oxidizing atmosphere such as a process in an inert gas such as a nitrogen gas or an argon gas, or a process in a vacuum.

The particle size depends to some extent on the reduction and heat treatment temperatures described above, but largely on the process of forming the iron and rhodium precipitates. For example, in general, the higher the alkali concentration and the higher the metal ion concentration, the larger the particle size of the obtained iron-rhodium alloy magnetic powder. In the present invention, by combining these conditions, 2
A magnetic powder having a particle size ranging from 0 nm to 200 μm was synthesized. Since the purpose of the present invention is to use this magnetic powder for a magnetic recording medium, the particle size is preferably in the range of about 50 nm to 50 μm.

Hereinafter, a medium using the iron-rhodium alloy magnetic powder will be described. The magnetic layer uses the above-described iron-rhodium alloy magnetic powder, and further adds the magnetic powder and the binder, and usually also an additive such as an abrasive, a dispersant or a lubricant, a carbon black, and the like. A magnetic paint was prepared by dispersing and mixing in an organic solvent, and the magnetic paint was applied on a non-magnetic support and dried to form a coating.

The binder used for the magnetic layer includes vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, vinyl chloride A combination of at least one selected from a hydroxyl group-containing alkyl acrylate copolymer resin, nitrocellulose, and the like with a polyurethane resin. Among them, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination. Polyurethane resins include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane,
There are polycarbonate polyurethane, polyester polycarbonate polyurethane and the like.

As described above, the binder is not particularly limited, and those generally used for magnetic recording media, such as those obtained by further adding a functional group to the binder, can be used.

The amount of the binder used is usually 5 to 50 parts by weight, preferably 10 to 35 parts by weight, based on 100 parts by weight of the alloy powder. In particular, when using a vinyl chloride resin as a binder, the ratio is preferably 5 to 30 parts by weight, and when using a polyurethane resin, the ratio is preferably 2 to 20 parts by weight, and these resins are used in combination at the above usage ratio. Is most preferred.

It is desirable to use together with these binders a thermosetting crosslinking agent that bonds to a functional group or the like contained in the binder to form a crosslink. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and the like, reaction products of these isocyanates with those having a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates are preferred. These crosslinking agents are generally used in a proportion of 15 to 70 parts by weight based on 100 parts by weight of the binder.

In order to improve the strength of the magnetic layer, it is preferable to use an abrasive generally used for magnetic recording media, such as α-alumina or α-alumina. The particle size of these abrasives is preferably 0.01 to 1 μm. Further, the use amount of these abrasives is usually 6 to 20 parts by weight, preferably 8 to 15 parts by weight, based on 100 parts by weight of the alloy powder, from the viewpoint of electromagnetic conversion characteristics and head contamination.

As one of the additives for the magnetic layer, a dispersant generally used for magnetic recording media, such as an alkylene oxide type or a glycerin type, may be used.

As another additive for the magnetic layer, a lubricant is preferably used. As the lubricant, conventionally known fatty acids, fatty acid esters, fatty acid amides, fatty acid metal salts, hydrocarbons, and the like can be used alone or in combination of two or more.

The amount of the additive to be used is preferably 0.5 to 5 parts by weight, more preferably 1 to 4 parts by weight, per 100 parts by weight of the magnetic powder. In addition, in the case of a lubricant such as a fatty acid, the amount is preferably 0.2 to 10 parts by weight with respect to 100 parts by weight of the powder,
More preferably, it is 0.5 to 5 parts by weight.

It is also possible to use a carbon black to reduce the friction coefficient of the magnetic layer and to prevent electrification. The amount of these carbon blacks to be used is preferably usually 3% by weight or less based on the powder.

In forming the magnetic layer, as the organic solvent used for preparing a paint, a lubricant solution, etc., any organic solvent conventionally used can be used.
For example, aromatic solvents such as benzene, toluene, and xylene; ketone solvents such as acetone, cyclohexanone, methyl ethyl ketone and methyl isobutyl ketone; acetate solvents such as ethyl acetate and butyl acetate; and carbonate esters such as dimethyl carbonate and diethyl carbonate. Hexane, tetrahydrofuran, dimethylformamide and the like, in addition to alcoholic solvents such as ethanol and isopropanol.

In preparing a magnetic coating material or the like, a conventionally known coating manufacturing process can be used, and it is particularly preferable to use a kneading step using a kneader or the like and a primary dispersion step together.
In the primary dispersion step, by using a sand mill,
This is desirable because the surface properties can be controlled while improving the dispersibility of the powder.

In the present invention, as the non-magnetic support,
Any conventionally used non-magnetic support for magnetic recording media can be used. Specifically, polyethylene terephthalate, polyesters such as polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamide imide, polysulfon, aramid, aromatic polyamide and the like, the thickness is usually 2 to 100 μm Plastic film is used.

The form of the magnetic recording medium is not particularly limited. For example, when used as a magnetic card, a magnetic layer containing an iron-rhodium alloy magnetic powder is provided on a substrate such as polyethylene terephthalate. be able to. Further, a magnetic layer containing an iron-rhodium alloy magnetic powder may be provided on the release base film, and the magnetic layer may be peeled off from the base film at the time of use, and may be pasted or embedded on a card substrate. Further, a thermal printing layer can be further provided on the magnetic layer. As will be described later,
In particular, when the heat-sensitive printing layer is provided on the magnetic layer, information such as character information can be simultaneously recorded on the printing layer and the magnetic layer by the printing thermal head.

A piece of the magnetic layer containing the iron-rhodium alloy magnetic powder may be attached to a part of the magnetic card by laminating or embedding the magnetic layer. In this case, the magnetic layer containing the iron-rhodium alloy magnetic powder can be used as a data carrier. Even when used as a data carrier, the method of use is not particularly limited.For example, when used as a magnetic card, it can be laminated or embedded in a part of a conventional magnetic layer, and can be used as a magnetic layer. It can also be formed on the opposite surface.

The case of using a magnetic card has been described by way of example. However, the use is not particularly limited to a magnetic card, and various uses such as a bar code can be used as a data carrier. Can be used for applications.

Further, when the temperature of the iron-rhodium alloy magnetic powder is raised to a temperature equal to or higher than the magnetic transition temperature and then lowered, the magnetic powder exhibits a saturation magnetization corresponding to the temperature last experienced. This property indicates that this magnetic powder can also be used as a temperature sensor. Details when the temperature sensor is used will be described in Examples.

Hereinafter, a case where the magnetic barcode is used for a special magnetic barcode will be described as an example. A magnetic barcode is usually produced by printing a magnetic ink containing a soft magnetic powder such as carbonyl iron in the form of a barcode. Since the magnetic powder is a soft magnetic material, the magnetic flux does not leak to the outside in a normal state. For this reason, even if a jig for observing a magnetic pattern such as a magnetic viewer is used, the magnetic pattern cannot be read, so that it has high security. However, since the printed barcode pattern rises more or less from the substrate surface, there is a disadvantage that the barcode pattern can be read. If a concealing layer is further applied on the magnetic barcode, this bulge can be concealed to some extent, but to completely conceal it, the concealment layer must be thickened, resulting in a large spacing loss and reduced magnetic barcode output. There is a problem of lowering.

Therefore, at present, the dummy bar is printed using a powder having no magnetization in the gap between the bar code patterns, thereby preventing the true bar code pattern from being decoded.

On the other hand, at the time of reading, a bias magnetic field is applied to this bar code pattern using a magnetic head,
Magnetize the new bar code part containing soft magnetic powder,
The bar code pattern is read by detecting magnetic flux leakage from the magnetic head.

As described above, the magnetic barcode is widely used at present because it has a security property that it is difficult to read a barcode pattern in a normal state.

On the other hand, the magnetic barcode has a great problem that only a specific barcode pattern can be formed because the barcode pattern is formed by a printing method. In order to form many types of bar code patterns, it is necessary to make necessary types of color separations and to exchange the plates each time printing is performed, so that the cost becomes extremely high.

On the other hand, there is a method of magnetically recording a bar code pattern on a normal magnetic recording medium by using a magnetic head. This method has an advantage that an arbitrary bar pattern can be easily formed.However, since the magnetic material has a coercive force, a leakage magnetic flux exists even in a normal state, and the bar code pattern can be easily read by a magnetic viewer or the like. There is a disadvantage. That is, a magnetic barcode using magnetic recording has an advantage that any barcode pattern can be easily formed at low cost, but has a disadvantage of low security.

On the other hand, when the magnetic layer using the iron-rhodium alloy magnetic powder of the present invention is applied to a magnetic barcode, the barcode pattern can be heated and recorded by a thermal head for printing or the like. That is, the unheated portion is antiferromagnetic and has no magnetization, but the heated portion undergoes magnetic transition to become ferromagnetic, so that magnetization is developed. Therefore, a barcode pattern can be formed by a combination of heating and non-heating. Since the iron-rhodium alloy magnetic powder is a soft magnetic powder having a very small coercive force,
Like a magnetic barcode for printing, magnetic flux does not leak out under normal conditions. Therefore, it is extremely difficult to read a barcode pattern with a magnetic viewer or the like.

Further, unlike the bar code pattern formed by the printing method, since the bar code pattern is formed on the magnetic layer, the surface is uniform, the bar code pattern swells, and there is no problem that the bar code pattern can be read visually. The result is a magnetic bar code with a high degree of performance. Also, unlike the printing method, the bar code pattern can be recorded by a printing thermal head or the like, so that the bar code pattern can be easily changed. For example, when applied to a card, the barcode pattern can be easily changed for each card.

As described above, for example, the iron-
When a magnetic layer using a rhodium-based alloy magnetic powder is applied to a magnetic barcode, an extremely powerful magnetic barcode combining only the advantages of a magnetic barcode formed by a printing method and a magnetic barcode formed by a magnetic recording method. A magnetic barcode having security can be provided.

As another application example, when a heat-sensitive printing layer is further provided on the magnetic layer using the iron-rhodium alloy magnetic powder of the present invention, the information printed on the printing layer by the printing thermal head can be used. Exactly the same information is recorded on the magnetic layer. Regardless of whether the information recorded on the magnetic layer is usually digital information or analog information, it is meaningless by itself unless signal processing is performed. However, in this example, characters and pictures can be recorded directly on the magnetic layer. Such recording is extremely difficult to achieve with a normal magnetic recording medium, and can only be realized with the magnetic recording medium of the present invention.

As another example utilizing the temperature dependence of the unique magnetic properties of the iron-rhodium alloy magnetic powder, an example applied to a temperature sensor will be described. Attached to an electronic device whose operating temperature range is limited, and detects the presence or absence of a usage situation exceeding the operating temperature range. Attached to products that require temperature control, such as frozen foods. Detects temperature history to see if it has been exposed to an environment that impairs quality, such as thawing during transport. By attaching to a magnetic medium, the presence or absence of a history of a low-temperature or high-temperature environment that may impair the function of the medium is detected.

As a method of detecting the temperature history, it is simple to measure the saturation magnetization and detect the corresponding temperature, but an engineering detection method such as the Kerr effect is also possible.

As described above, the case where the present invention is applied to a recording medium capable of directly recording magnetic barcodes and characters and picture information, and the case where it is used as a temperature sensor have been described by way of example. By utilizing the temperature dependence of the unique magnetic properties of the powder, it is possible to develop a very unique application that has been impossible in the past.

Hereinafter, the present invention will be described with reference to examples.

(Example 1) (A) Preparation of iron-rhodium alloy magnetic powder 0.001 mol of iron (III) nitrate and 0.001 mol of rhodium (III) nitrate were dissolved in 50 cc of water. Separately from this nitrate aqueous solution, 0.006 mol of sodium hydroxide was dissolved in 50 cc of water. A nitrate co-precipitate was prepared by adding a nitrate aqueous solution to this aqueous solution of sodium hydroxide, and then heated at 100 ° C. to produce a precipitate of an oxide of iron and rhodium. The precipitate suspension was washed with water until the pH became 8 or less, and then filtered to remove the precipitate.

Next, this precipitate was spread on a vat,
After drying at 400C for 4 hours, a heat treatment was performed at 400C for 1 hour to produce an oxide of iron and rhodium.

This oxide was reduced by heating at 500 ° C. for 2 hours in a hydrogen stream to produce an iron-rhodium alloy magnetic powder. Next, the mixture was cooled to room temperature with flowing hydrogen gas and taken out into the air to obtain an iron-rhodium alloy magnetic powder.

The iron and rhodium contents of this iron-rhodium alloy magnetic powder were examined by emission spectrometry.
When expressed as _1-x Rh _x , it was found that x was 0.488. The particle size was about 0.15 μm.

FIG. 1 shows the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder. Table 1 shows the results obtained by summarizing the main magnetic characteristics such as the magnetic transition temperature and the saturation magnetization changed by the magnetic transition.

(B) Preparation of Medium After the following magnetic coating component (1) was kneaded with a kneader, dispersed in a sand mill with a residence time of 45 minutes, the following magnetic coating component (2) was added, and the mixture was stirred and filtered. Thus, a magnetic paint was prepared.

<Magnetic paint component (1)> 100 parts of iron-rhodium alloy magnetic powder produced in (A) above (iron / alloy powder: 50 atomic%, rhodium / alloy particles: 50 atomic%) vinyl chloride-hydroxy chloride Propyl acrylate copolymer 8 parts (Contains -SO3 Na group: 0.7 × 10-4 equivalents / g) Polyester polyurethane resin 4 parts (Contains -SO3 Na group: 1.0 × 10-4 equivalents / g) α- Alumina (average particle diameter: 0.4 μm) 10 parts Carbon black (average particle diameter: 100 nm) 1.5 parts Myristic acid 1.5 parts Methyl ethyl ketone 133 parts Toluene 100 parts <Magnetic paint component (2)> Stearic acid 1.5 Part Polyisocyanate 4 parts Cyclohexanone 133 parts Toluene 33 parts This magnetic paint was coated with a 260 μm thick polyethylene terephthalate film. The thickness after drying was coated to be about 10 [mu] m. The coated sheet was punched out into a card size to obtain a sample for evaluation.

(C) Method of Measuring Temperature Dependence of Saturation Magnetization of Iron-Rhodium Alloy Magnetic Powder The iron-rhodium alloy magnetic powder thus obtained was subjected to a magnetic field of 16 kOe using a sample vibration magnetometer. The temperature dependence of the saturation magnetization was measured with the voltage applied. The measuring method is as follows.

After the iron-rhodium alloy magnetic powder was filled in a copper measuring container, it was attached to a sample vibration magnetometer, covered with a quartz protective tube, and evacuated to prevent oxidation of the sample due to heating. A heater for heating and a dual bottle for measurement at a lower temperature were attached to the quartz tube. In order to further improve heat conduction, about 10 Torr of argon gas was introduced into the quartz tube. Next, liquid nitrogen was put into this dual bottle, and once cooled to the temperature of liquid nitrogen, a current was passed through the heater to overheat. When the sample temperature reached about minus 100 ° C., a magnetic field of 16 kOe was applied to start measuring the temperature dependence of the saturation magnetization. About minus 100 ° C
The temperature dependence of the saturation magnetization was measured while increasing the temperature at a rate of 2 ° C./min. After heating to about 350 ° C,
The temperature was lowered to room temperature at the same rate, and the temperature was lowered to about minus 100 ° C. while gradually adding liquid nitrogen. As described above, a hysteresis curve with respect to the temperature of the saturation magnetization due to heating and cooling in a temperature range of about minus 100 ° C. to about 350 ° C. was measured.

(D) Evaluation method of iron-rhodium-based alloy magnetic powder medium The card-shaped iron-rhodium-based alloy magnetic powder medium produced by the above method was evaluated by using a reader equipped with a printing thermal head. A writer was used. Assuming a bar code recording, a rectangular mark having a width of about 2 mm and a length of about 5 mm was heated and printed at intervals of about 2 mm using this printing head.

Next, the bar code reading magnetic head is
The rectangular character string was scanned, and the head reproduction output obtained from the rectangular character string was measured by observing the waveform of an oscilloscope. The bar code reading magnetic head can apply a bias magnetic field.
The rectangular character heated by the thermal printing head is turned into a ferromagnetic material, magnetized by a bias magnetic field applied at the same time as reproduction, generates a leakage magnetic field, and is reproduced by the magnetic head as a signal output.

(Example 2) In the preparation of the iron-rhodium alloy magnetic powder of (A) in Example 1, 0.001 mol of iron (III) nitrate and 0.001 mol of rhodium (III) nitrate were used.
In place of 0.00096 moles of iron (III) nitrate;
A coprecipitate was formed in the same manner as in Example 1, except that rhodium (III) nitrate of 00104 was dissolved in 50 cc of water.
After washing with water, filtration, drying, and heat reduction, an iron-rhodium alloy magnetic powder was prepared.

This iron-rhodium alloy magnetic powder is made of Fe
When represented by _1-x Rh _x , it was found that x was 0.505. The particle size was 0.13 μm.

FIG. 2 shows the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder. Table 1 summarizes main magnetic characteristics such as the magnetic transition temperature and the amount of saturation magnetization changed by the magnetic transition.

Further, using this iron-rhodium alloy magnetic powder, a magnetic recording medium was produced in the same manner as in Example 1.

Example 3 In the preparation of the iron-rhodium alloy magnetic powder of (A) in Example 1, 0.001 mol of iron (III) nitrate and 0.001 mol of rhodium (III) nitrate were used.
In place of 0.00082 moles of iron (III) nitrate,
A coprecipitate was formed in the same manner as in Example 1 except that rhodium (III) nitrate of 00118 was dissolved in 50 cc of water.
After washing with water, filtration, drying, and heat reduction, an iron-rhodium alloy magnetic powder was prepared.

This iron-rhodium alloy magnetic powder is made of Fe
When expressed as _1-x Rh _x , it was found that x was 0.540. The particle size was 0.11 μm.

FIG. 3 shows the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder. Table 1 summarizes main magnetic characteristics such as the magnetic transition temperature and the saturation magnetization that changes with the magnetic transition.

Further, a magnetic recording medium was produced in the same manner as in Example 1 using this iron-rhodium alloy magnetic powder.

Example 4 In the preparation of the iron-rhodium alloy magnetic powder of (A) in Example 1, 0.001 mol of iron (III) nitrate and 0.001 mol of rhodium (III) nitrate were used.
In place of 0.0099 mol of iron (III) nitrate,
Dissolve 10001 moles of rhodium (III) nitrate in 50 cc of water and use ammonia water instead of sodium hydroxide as an alkali to form a coprecipitate until the pH of the suspension is 9 A coprecipitate was formed, washed with water, filtered, dried, and then heat-reduced to produce an iron-rhodium-based alloy magnetic powder in the same manner as in Example 1 except that the mixture was neutralized by adding aqueous ammonia.

This iron-rhodium alloy magnetic powder is made of Fe
When represented by _1-x Rh _x , it was found that x was 0.504. The particle size was 0.12 μm.

FIG. 4 shows the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder. Table 1 summarizes main magnetic characteristics such as the magnetic transition temperature and the saturation magnetization that changes with the magnetic transition.

Further, using this iron-rhodium alloy magnetic powder, a magnetic recording medium was produced in the same manner as in Example 1.

Example 5 The procedure of Example 4 was repeated except that the prepared iron-rhodium alloy magnetic powder was vacuum-sealed in a quartz tube and heat-treated at 600 ° C. for 2 days. -A rhodium alloy magnetic powder was prepared.

This iron-rhodium alloy magnetic powder is made of Fe
When expressed as _1-x Rh _x , x was 0.504 and the particle size was 0.15 μm.

FIG. 5 shows the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder. Table 1 summarizes main magnetic characteristics such as the magnetic transition temperature and the saturation magnetization that changes with the magnetic transition.

FIG. 6 shows an X-ray diffraction diagram of the iron-rhodium-based magnetic powder. In addition to sharp diffraction lines based on iron-rhodium alloys, diffraction lines based on slightly metallic rhodium are observed.

Further, using this iron-rhodium alloy magnetic powder, a magnetic recording medium was produced in the same manner as in Example 1.

Example 6 An iron-rhodium alloy was prepared in the same manner as in Example 4 except that the prepared iron-rhodium alloy magnetic powder was heat-treated in a vacuum-sealed quartz tube at 500 ° C. for 7 days. A system alloy magnetic powder was produced.

The iron-rhodium alloy magnetic powder is made of Fe
When expressed as _1-x Rh _x , x was 0.504 and the particle size was 0.13 μm.

Table 1 shows the main magnetic properties of the iron-rhodium-based magnetic powder, such as the magnetic transition temperature and the saturation magnetization changed by the magnetic transition.

Example 7 An iron-rhodium alloy was prepared in the same manner as in Example 4 except that the prepared iron-rhodium alloy magnetic powder was heat-treated at 550 ° C. for 2 days in a vacuum-sealed quartz tube. A system alloy magnetic powder was produced.

The iron-rhodium alloy magnetic powder is made of Fe
When represented by _1-x Rh _x , x was 0.504 and the particle size was 0.14 μm.

Table 1 summarizes the main magnetic properties of the iron-rhodium-based magnetic powder, such as the magnetic transition temperature and the amount of saturation magnetization changed by the magnetic transition.

Example 8 The procedure of Example 4 was repeated, except that the prepared iron-rhodium alloy magnetic powder was heat-treated at 600 ° C. for 4 days in a vacuum-sealed quartz tube. A system alloy magnetic powder was produced.

The iron-rhodium alloy magnetic powder is made of Fe
When expressed as _1-x Rh _x , x was 0.504 and the particle size was about 0.2 μm.

Table 1 shows the main magnetic properties of the iron-rhodium-based magnetic powder, such as the magnetic transition temperature and the saturation magnetization changed by the magnetic transition.

Example 9 In the preparation of the iron-rhodium-based alloy magnetic powder of (A) in Example 1, 0.001 mol of iron (III) nitrate and 0.001 mol of rhodium (III) nitrate were used.
In place of 0.00104 moles of iron (III) nitrate;
A coprecipitate was formed, washed with water, filtered, dried, and then reduced by heating in the same manner as in Example 1 except that 0096 mol of rhodium (III) nitrate was dissolved in 50 cc of water to obtain an iron-rhodium alloy. A magnetic powder was produced.

This iron-rhodium alloy magnetic powder is made of Fe
When expressed as _1-x Rh _x , it was found that x was 0.492. The particle size was 0.11 μm.

FIG. 7 shows the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder. Table 1 summarizes main magnetic characteristics such as the magnetic transition temperature and the saturation magnetization that changes with the magnetic transition.

(Examples 10-13) In Example 3,
0.00082 mole of iron (III) nitrate and 0.00118
Further, palladium nitrate was added to rhodium (III) nitrate. The amount of palladium nitrate added is 0.000
01 mol (Example 10), 0.00002 mol (Example 11), 0.00004 mol (Example 12), 0.00
008 mol (Example 13) was prepared by changing four kinds.

Otherwise, a coprecipitate was formed, washed with water, filtered, dried and reduced by heating to produce an iron-rhodium alloy magnetic powder containing palladium, in the same manner as in Example 3.

The particle size of the iron-rhodium alloy magnetic powder containing palladium ranges from 0.10 μm to 0.1 μm.
It was in the range of 15 μm.

FIG. 8 shows the temperature dependence of the saturation magnetization of the palladium-containing iron-rhodium alloy magnetic powder prepared in Example 12 as an example. Note The palladium added iron - rhodium alloy magnetic powder when expressed in _{Fe 1-xy Rh x Pd y} , x is 0.523, y is found to be 0.018. The particle size was 0.12 μm.

Table 1 shows that these palladium-containing iron-
The main magnetic properties, such as the composition of the rhodium-based alloy magnetic powder and the magnetic transition temperature and the amount of saturation magnetization that changes according to the magnetic transition, are summarized below.

Example 14 The procedure of Example 12 was repeated, except that the palladium-containing iron-rhodium alloy magnetic powder prepared in Example 12 was vacuum-sealed in a quartz tube and heat-treated at 600 ° C. for 2 days. A palladium-containing iron-rhodium alloy magnetic powder was prepared.

The particle size of the palladium-containing iron-rhodium alloy magnetic powder was 0.13 μm. Table 1 summarizes the main magnetic properties of the palladium-containing iron-rhodium-based alloy magnetic powder, such as the composition and the magnetic transition temperature and the amount of saturation magnetization that changes with the magnetic transition.

Further, using this palladium-containing iron-rhodium alloy magnetic powder, a method similar to that of Example 1 was used.
A magnetic recording medium was manufactured.

Comparative Example 1 In the preparation of the iron-rhodium alloy magnetic powder of (A) in Example 1, 0.001 mol of iron (III) nitrate and 0.001 mol of rhodium (III) nitrate were used.
Instead of 0.001224 mol of iron (III) nitrate,
A coprecipitate was formed in the same manner as in Example 1 except that 0.0007776 of rhodium (III) nitrate was dissolved in 50 cc of water, washed with water, filtered, dried and reduced by heating to obtain an iron-rhodium alloy. A magnetic powder was produced.

This iron-rhodium alloy magnetic powder is made of Fe
When represented by _1-x Rh _x , it was found that x was 0.371. The particle size was about 0.32 μm.

FIG. 9 shows the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder. Table 1 shows the main magnetic properties of the magnetic powder. Further, using this iron-rhodium alloy magnetic powder, a magnetic recording medium was produced in the same manner as in Example 1.

Comparative Example 2 In the preparation of the iron-rhodium alloy magnetic powder of (A) in Example 1, 0.001 mol of iron (III) nitrate and 0.001 mol of rhodium (III) nitrate were used.
Instead, a coprecipitate was formed, washed with water, filtered, dried, and then reduced by heating in the same manner as in Example 1 except that 0.002 mol of iron (III) nitrate was dissolved in 50 cc of water. A magnetic powder of only iron without rhodium was produced.

The particle size of the iron magnetic powder is 0.6 μm.
Met. FIG. 10 shows the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder. Table 1 shows the magnetic properties such as the saturation magnetization of the iron magnetic powder.

Further, in Example 1 using this iron magnetic powder,
A magnetic recording medium was manufactured in the same manner as described above.

<Measurement Results of Temperature Dependence of Saturation Magnetization Amount of Iron-Rhodium Alloy Magnetic Powder> FIGS.
7 shows the iron-rhodium alloy magnetic powder produced in Example 5, FIG. 7 shows the iron-rhodium alloy magnetic powder produced in Example 9, and FIG. 8 shows the palladium-containing iron-rhodium alloy produced in Example 12. 9 shows the temperature dependence of the saturation magnetization of the iron-rhodium alloy magnetic powder produced in Comparative Example 1, and FIG. 10 shows the temperature dependence of the saturation magnetization of the iron magnetic powder produced in Comparative Example 2.

Example 1 represented by Fe _0.512 Rh _0.488
As shown in FIG. 1, the iron-rhodium alloy magnetic powder exhibits a saturation magnetization of about 20 emu / g at a temperature of about 100 ° C. or less. This saturation magnetization is considered to be due to the appearance of saturation magnetization due to iron present in addition to the iron-rhodium alloy magnetic powder.

On the other hand, when the temperature of the magnetic powder is raised to 100 ° C. or more, the iron-rhodium alloy magnetic powder changes from antiferromagnetic to ferromagnetic by magnetic transition at a temperature of 120 to 140 ° C., and the saturation magnetization is about 120 emu. / G rapidly increases. When the temperature is further increased, the saturation magnetization slightly decreases and shows a value of 90 emu / g at about 300 ° C.

Next, when the temperature is lowered from 300 ° C., the original magnetization curve is followed up to about 140 ° C. where magnetic transition occurs.
At 40 ° C. or lower, hysteresis is exhibited without following the original curve. That is, for example, at 120 ° C. where the magnetic transition starts, about 120 ° C.
It shows a saturation magnetization of emu / g, and shows a saturation magnetization of about 75 emu / g even when the temperature is lowered to room temperature of 20 ° C.
When the temperature is further decreased to about minus 100 ° C., the saturation magnetization becomes about 20 emu / g, which is almost the initial value, indicating that the iron-rhodium alloy magnetic powder returns to the antiferromagnetic state before the temperature rise. .

FIG. 2 shows the temperature dependence of the saturation magnetization of the iron-rhodium alloy magnetic powder of Example 2 represented by Fe _0.495 Rh _0.505 . As in Example 1, about 120 to 14
It shows a magnetic transition at 0 ° C. and has a saturation magnetization of about 100 emu.
/ G rapidly increases. On the other hand, the saturation magnetization before magnetic transition is as small as about 5 emu / g. This is because the magnetic powder is almost composed of an iron-rhodium alloy magnetic powder, so that it is in an antiferromagnetic state before magnetic transition and has no magnetization. Further, when the magnetic powder is almost composed of the iron-rhodium alloy magnetic powder, an extremely large change in saturation magnetization of about 100 emu / g before and after the magnetic transition is exhibited. Also in the magnetic powder of Example 2, the saturation magnetization shows remarkable temperature hysteresis.

FIG. 3 shows the temperature dependence of the saturation magnetization of the iron-rhodium alloy magnetic powder of Example 3 represented by Fe _0.460 Rh _0.540 . Almost no saturation magnetization is observed before the magnetic transition, but the saturation magnetization is 80 em due to the magnetic transition.
u / g. It is conceivable that the iron-rhodium-based alloy magnetic powder of this embodiment contains, in addition to the iron-rhodium-based alloy, unreacted rhodium having no magnetism.
Therefore, before the magnetic transition, since it is composed of an antiferromagnetic iron-rhodium-based alloy and non-magnetic rhodium, it is considered that almost no saturation magnetization is observed. On the other hand, the reason why the saturation magnetization after the magnetic transition is smaller than that of the magnetic powder of Example 2 is considered that the amount of the iron-rhodium-based alloy formed in the magnetic powder is smaller than that of the magnetic powder of Example 2. Can be Even in this magnetic powder, remarkable hysteresis is still observed due to the magnetic transition.

FIG. 4 shows the temperature dependence of the saturation magnetization of the iron-rhodium alloy magnetic powder of Example 4. When ammonia is used as an alkali at the time of producing the coprecipitate of iron and rhodium, it has a composition of Fe _0.496 Rh _0.504 . Since the composition of this magnetic powder is close to that of the iron-rhodium alloy magnetic powder of Example 2, it shows a temperature dependence of the saturation magnetization similar to that of the iron-rhodium alloy magnetic powder of Example 2 shown in FIG. .
That is, at a temperature of about 120 to 140 ° C., the saturation magnetization rapidly increases due to the magnetic transition, and about 100 emu before and after the magnetic transition.
/ G and a remarkable hysteresis of the saturation magnetization when the temperature rises and when the temperature falls.

FIG. 5 shows the temperature dependence of the saturation magnetization of the iron-rhodium alloy magnetic powder of Example 5. The iron-rhodium alloy magnetic powder produced in Example 4 was further vacuum-sealed in a quartz tube and heat-treated at 600 ° C. for 2 days. The composition of the iron-rhodium-based alloy magnetic powder is the same as that of the iron-rhodium-based alloy magnetic powder of Example 4, but the magnetic transition temperature range is 110 compared to the iron-rhodium-based alloy magnetic powder of Example 4. From 115 ℃ to sharp,
And the variation of the saturation magnetization before and after the magnetic transition is about 100 em
It shows a large value of u / g. This is presumably because the crystallinity of the iron-rhodium alloy was improved by the heat treatment, and the abundance of the iron-rhodium alloy itself was also increased.

FIG. 6 shows an X-ray diffraction pattern of the iron-rhodium alloy magnetic powder of Example 5. A sharp diffraction peak based on the iron-rhodium alloy is observed. Further, in addition to the iron-rhodium alloy, a minute diffraction peak based on a small amount of unreacted metal rhodium is also observed.

FIG. 7 shows the temperature dependence of the saturation magnetization of the iron-rhodium alloy magnetic powder of Example 9 represented by Fe _0.508 Rh _0.492 . The saturation magnetization before magnetic transition is about 65e
At mu / g, the saturation magnetization increases to about 120 emu / g due to the magnetic transition at 120-140 ° C. Since the iron-rhodium-based alloy magnetic powder of this example has a high iron content, it is considered that the unreacted iron having ferromagnetism exhibits a large saturation magnetization before the magnetic transition.

FIG. 8 shows the palladium-containing iron of Example 12.
4 shows the temperature dependence of the saturation magnetization of a rhodium-based magnetic powder.
This magnetic powder is represented by Fe _0.459 Rh _0.523 Pd _0.018 . The magnetic transition temperature is iron-free without palladium.
It is much lower than rhodium-based magnetic powder,
Magnetic transition occurs at 70 ° C. The saturation magnetization before the magnetic transition is about 15 emu / g, and about 70 emu / g due to the magnetic transition.
To increase. It has been found that by adding Pd in this way, it is possible to control the magnetic transition temperature, particularly to the low temperature side. The present inventors have also found that as the amount of Pd added increases, the magnetic transition temperature shifts to a lower temperature side.

FIG. 9 shows the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder of Comparative Example 1. This magnetic powder is F
e It is represented by _0.629 Rh _0.371 and has a high iron content.
It no longer shows a magnetic transition like the iron-rhodium-based magnetic powder of the examples, and the saturation magnetization monotonically decreases as the temperature increases.

FIG. 10 shows the temperature dependence of the saturation magnetization of the magnetic powder of Comparative Example 2 made only of iron containing no rhodium. As is apparent from the figure, the magnetic powder containing only iron does not show any magnetic transition.

As described above, it can be seen that the iron-rhodium alloy magnetic powder of the present invention exhibits extremely unique magnetic properties completely different from conventional magnetic powder.

That is, when the temperature rises, the transition from antiferromagnetic to ferromagnetic due to magnetic transition causes the saturation magnetization to increase sharply. Once the magnetic transition occurs, the saturation magnetization does not return to the original state when the temperature drops, and the remarkable saturation magnetization increases. Shows the temperature hysteresis. Such a peculiar phenomenon is a phenomenon first discovered by the present inventors in the magnetic powder of the present invention, and its value in practical use as well as its academic value is immeasurably large.

The present inventors have also focused on the control of the magnetic transition temperature, with the aim of expanding the applications in practical use. As a result, they have found that it is possible to control the magnetic transition temperature in a wide temperature range by adding a noble metal element such as palladium or ruthenium as an additional element to iron or rhodium.

Further, it has been found that the particle size of the iron-rhodium alloy magnetic powder and the heat treatment temperature also affect the magnetic transition temperature, and that the temperature is particularly important in practical use.
It has been found that the magnetic transition temperature can be controlled in a temperature range of 00 ° C.

As is clear from FIGS. 1 to 5 and FIGS. 7 and 8, when the temperature is cooled to a low temperature of 0 ° C. or less, the saturation magnetization returns to the value of the saturation magnetization before the magnetic transition. That is, it indicates that the state returns to the initial state before heating to a temperature higher than the magnetic transition temperature.
This property is extremely effective in practical use, and shows that data can be returned to the initial state and rewritten by cooling data recorded by heating with a thermal head or the like.

The iron-rhodium alloy magnetic powder prepared in Examples 1 to 9, the palladium-containing iron-rhodium alloy magnetic powder prepared in Examples 10 to 14, and the iron-rhodium alloy magnetic powder prepared in Comparative Example 1 Further, in Comparative Example 2, the composition of the iron magnetic powder, the magnetic transition temperature (Ttrs), the change in the saturation magnetization due to the magnetic transition (ΔMtrs), the saturation magnetization before the magnetic transition (Mint), and the saturation magnetization after the magnetic transition (Mtra
s), and the saturation magnetization (Mrmt) at 20 ° C. when the temperature is raised to a temperature equal to or higher than the magnetic transition temperature and lower than the temperature at which the magnetic transition occurs, and ΔMdif which is the difference between Mrmt and Mint.
Are summarized in Table 1.

The magnetic transition temperature was defined as an intermediate temperature between the temperature at which the magnetic transition starts and the temperature at which the magnetic transition ends. When the temperature is further increased after the magnetic transition, the saturation magnetization decreases. Therefore, the saturation magnetization after the magnetic transition is the maximum saturation magnetization after the transition.

[0158]

[Table 1]

As is clear from Table 1, the iron-rhodium-based magnetic powder and the palladium-added iron-rhodium-based magnetic powder shown in the examples have magnetic transition temperatures (Ttrs) and changes in saturation magnetization due to magnetic transition (Ttrs). ΔMtrs), saturation magnetization before magnetic transition (Mint), saturation magnetization after magnetic transition (Mtra
s) and the saturation magnetization (Mrmt) at 20 ° C. when the temperature was raised to a temperature higher than the magnetic transition temperature and lower than the temperature at which the magnetic transition occurred, and the rhodium content shown in Comparative Example 1 was observed. In the iron-rhodium-based magnetic powder having a small amount of iron and the conventional iron magnetic powder containing no rhodium shown in Comparative Example 2, only the saturation magnetization (Mrmt) at 20 ° C. was observed, and other characteristics were observed. Absent.

In this embodiment, the magnetic transition temperature (Ttrs)
Although it is in the range of 51 ° C. to about 128 ° C., as described above, the transition temperature can be increased by adding elements such as palladium and ruthenium to iron and rhodium, or by changing the particle size and heat treatment conditions. ℃ ~ 200 ℃
It can be prepared in the temperature range of Such a magnetic transition temperature is a particularly preferable temperature when performing recording by heating with a thermal head for printing.

In this embodiment, the variation (ΔMtrs) of the saturation magnetization due to the magnetic transition is 52 emu / g to 99 emu.
It is 10 emu / g to 200 emu / g by changing the additive element and the heat treatment conditions similarly to the magnetic transition temperature.
It can be prepared in the range of emu / g.

The saturation magnetization (Mint) before the magnetic transition and the saturation magnetization (Mtras) after the magnetic transition greatly depend on the composition. In particular, when the iron content is too large, the saturation magnetization before the magnetic transition becomes large. Although the saturation magnetization after the magnetic transition increases, the change in the saturation magnetization due to the magnetic transition tends to decrease. When the content of rhodium increases, both the saturation magnetization before the magnetic transition and the saturation magnetization after the magnetic transition tend to decrease. When the rhodium content is too high, the magnetic transition does not appear. In the present invention, as in the case of the magnetic transition temperature, the saturation magnetization (Mint) before the magnetic transition ranges from 0 emu / g to 80 emu / g, and the saturation magnetization after the magnetic transition, The quantity (Mtras) is 20
It can be prepared in the range of emu / g to 200 emu / g.

ΔMdif, which is the difference between the saturation magnetization (Mrmt) at 20 ° C. and the saturation magnetization (Mint) before the magnetic transition when the temperature is lowered to a temperature lower than the temperature at which the magnetic transition occurs, affects the output during reproduction of the magnetic head. In the present embodiment, ΔMdif is in the range of 16 emu / g to 61 emu / g, which is a sufficiently high value for reproducing with a magnetic head. Also, this ΔMdif can be adjusted in the range of 5 emu / g to 100 emu / g by changing the additive element and the heat treatment conditions.

On the other hand, it goes without saying that ΔMdif does not exist in the magnetic powder containing only iron, which is a normal magnetic powder (Comparative Example 2).

<Evaluation Results of Iron-Rhodium-Based Alloy Magnetic Powder Medium> The iron-rhodium-based alloy magnetic powder produced in each of the examples and comparative examples was converted into a card-shaped medium by the method described in the first embodiment. The evaluation was performed according to the method described above.

Approximately 2 m wide by printing thermal head
A rectangular mark having a length of about 5 mm and a length of about 5 mm was printed by heating at intervals of about 2 mm. That is, a rectangular mark having a width of about 2 mm was heated and recorded, and then a width of about 2 mm was recorded in an unheated combination for a width of about 10 mm. In this case, since the thermal printing layer is not formed, the operation is the same as that of the thermal printing recording. However, since the magnetic layer is simply heated by the thermal head, no change is visually observed.

Next, the bar code reading magnetic head is
The rectangular mark array was scanned, and the head reproduction output obtained from the rectangular mark array was measured by observing the waveform of an oscilloscope. Since the magnetic head for reading a bar code can apply a bias magnetic field, a portion heated by the thermal head is magnetically transferred to a ferromagnetic material, and is magnetized by the bias magnetic field applied at the time of reproduction, thereby causing a leakage magnetic field. And reproduced by a magnetic head as a signal output.

On the other hand, the portion that is not heated is a state in which a ferromagnetic substance and an antiferromagnetic substance due to an excess of iron are mixed as an antiferromagnetic substance. When magnetized even when a bias magnetic field is applied, a change in the amount of saturation magnetization due to a magnetic transition from an antiferromagnetic material to a ferromagnetic material occurs as a difference in the leakage magnetic field.
Therefore, when this portion is scanned by the magnetic head, a change in the leakage magnetic field is detected by the magnetic head as a reproduction output. The reproduced output was obtained from the amplitude of the reproduced waveform observed with an oscilloscope.

Table 2 shows the measurement results of the iron-rhodium alloy magnetic powder media of Examples and Comparative Examples. The reproduction output of the iron-rhodium-based alloy magnetic powder medium of Example 2 was set to 100% and the relative output was shown.

[0170]

[Table 2]

As is clear from Table 2, the medium using the iron-rhodium-based alloy magnetic powder of the embodiment of the present invention can be recorded by a thermal head for printing, and has a sufficiently high sensitivity by a magnetic head for a magnetic barcode. It can be seen that it can be read.

On the other hand, a magnetic recording medium using the magnetic powder of Comparative Example 1 which does not show a magnetic transition even with an iron-rhodium alloy magnetic powder, and a Comparative Example 2 comprising only iron magnetic powder which is a normal magnetic powder In the magnetic recording medium described above, no change in saturation magnetization due to heating by the thermal head occurs, and no reproduction output is obtained.

Next, an example of application as a temperature sensor will be described.

The temperature dependence of the saturation magnetization of the magnetic recording medium of Example 5 shown in FIG. 5 was used as the reference hysteresis. As a method, the temperature history is detected by measuring the value of the saturation magnetization at 100 ° C. First, the temperature of the recording medium of Example 5 is raised to 160 ° C., and is lowered by natural heat radiation. Next, the temperature is stopped when the saturation magnetization reaches 100 emu / g. The magnetization at this time is defined as the temperature stop magnetization, and the temperature is defined as the temperature stop temperature. The temperature is further increased to 100 ° C., and the saturation magnetization is measured. The detected temperature is determined by comparing the measured saturation magnetization with the reference hysteresis. This operation was repeated to measure the temperature-fall stop magnetization and the temperature-fall stop temperature, and collated with the reference hysteresis to determine the detected temperature.
The results are summarized in Table 3.

[0175]

[Table 3]

As is evident from Table 3, the detected temperature obtained from the reference hysteresis coincides with the actually measured temperature drop stop temperature with an accuracy of about ± 2 ° C. This indicates that the magnetic recording medium using powder can be used sufficiently as a temperature sensor.

The above results have been described by exemplifying a case where the present invention is applied to a data carrier such as a magnetic barcode or a device such as a temperature sensor. By utilizing the temperature dependence of unique magnetic properties of magnetic recording media using powder,
Further, a wide range of applications can be developed.

[0178]

As described above, when the iron-rhodium alloy magnetic powder of the present invention is applied to a magnetic recording medium,
It is possible to develop extremely unique applications that could not be realized with conventional magnetic powders and magnetic recording media, such as data carriers and temperature sensors, opening up new industrial fields. Therefore, the magnetic powder of the present invention and the magnetic recording medium using the magnetic powder have invaluable industrial utility.

[Brief description of the drawings]

FIG. 1 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder of Example 1.

FIG. 2 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder of Example 2.

FIG. 3 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder of Example 3.

FIG. 4 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder of Example 4.

FIG. 5 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder of Example 5.

6 is an X-ray diffraction diagram of the iron-rhodium-based magnetic powder of Example 5. FIG.

FIG. 7 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder of Example 9.

FIG. 8 is a graph showing the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder of Example 12.

FIG. 9 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder of Comparative Example 1.

FIG. 10 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder of Comparative Example 2.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01F 1/06 H01F 1/06 LS (72) Inventor Shinichi Kitahata 1-88 Ushitora 1-chome Ushitora, Ibaraki-shi, Osaka No. Hitachi Maxell Co., Ltd. (72) Inventor Yuji Sasaki 1-88, Ushitora, Ibaraki City, Osaka Prefecture F-term (reference) 4K018 AA02 AA25 BA01 BA14 BC01 BC40 BD02 CA50 KA43 5D006 BA05 BA08 DA01 5D112 AA05 AA28 BB02 BB07 GA30 GB01 5E040 AA11 AA19 BB03 CA06 HB09 HB11 HB17 NN01 NN06 NN15 NN17 NN18

Claims (23)

[Claims] 1. An iron-rhodium alloy magnetic powder containing at least iron and rhodium as constituent elements, wherein x is 0.4 or more and 0 or more when an iron-rhodium alloy component is represented by Fe _1-x Rh _x. 0.8 and the particle size is 20 nm or more and 20
An iron-rhodium-based alloy magnetic powder having a particle size of 0 μm or less. 2. At least one member selected from the group consisting of ruthenium, palladium, iridium, platinum and osmium.
0.1 to 10% by mole of rhodium
The iron-rhodium-based alloy magnetic powder according to claim 1, wherein the magnetic powder is contained. 3. The iron-rhodium-based alloy magnetic powder according to claim 1, wherein the saturation magnetization changes due to magnetic transition in a temperature range of 30 ° C. to 200 ° C. 4. The amount of change in the saturation magnetization due to the magnetic transition is:
4. The iron-rhodium-based alloy magnetic powder according to claim 3, wherein the magnetic powder is in the range of 10 emu / g to 200 emu / g. 5. The iron-rhodium alloy magnetic powder according to claim 3, wherein the magnetic transition is a transition from antiferromagnetic to ferromagnetic. 6. The saturation magnetization before magnetic transition is 0 emu / g.
4. The iron-rhodium-based alloy powder according to claim 3, wherein the saturation magnetization after the magnetic transition is from 20 emu / g to 200 emu / g. 7. The iron according to claim 3, wherein, in the step of raising the temperature above the magnetic transition temperature and then lowering the temperature below the temperature at which the magnetic transition occurs, a change in the saturation magnetization with respect to the temperature indicates hysteresis. -Rhodium alloy powder. 8. The method according to claim 1, wherein the saturation magnetization at 20 ° C. when the temperature is raised to a temperature higher than the magnetic transition temperature and lower than the temperature at which the magnetic transition occurs is in the range of 10 emu / g to 150 emu / g. The iron-rhodium alloy powder according to claim 7. 9. The difference between the saturation magnetization at 20 ° C. when the temperature rises above the magnetic transition temperature and falls below the temperature at which the magnetic transition occurs and the saturation magnetization before the magnetic transition is 10 emu /
The iron-rhodium-based alloy powder according to claim 7, wherein the iron-rhodium-based alloy powder is in a range from g to 100 emu / g. 10. A method for producing an iron-rhodium alloy magnetic powder, wherein an aqueous solution containing iron and rhodium ions and an alkaline aqueous solution are mixed to produce a precipitate containing iron and rhodium, and this precipitate is reduced by heating. Thereby producing an iron-rhodium-based alloy magnetic powder. 11. A method for producing an iron-rhodium alloy magnetic powder, comprising: iron and rhodium; and at least one element selected from ruthenium, palladium, iridium, platinum and osmium in a molar ratio to rhodium. An aqueous solution containing these ions and an aqueous alkaline solution are mixed so that the concentration becomes 0.1 to 10%, a precipitate containing these elements is prepared, and the precipitate is heated and reduced to obtain iron-rhodium. A method for producing an iron-rhodium-based alloy magnetic powder, characterized in that the powder is an iron-based alloy magnetic powder. 12. In the step of mixing an aqueous solution containing iron and rhodium ions and an alkaline aqueous solution to produce a precipitate containing iron and rhodium, the pH after mixing is from 6 to 10
12. The method according to claim 10, wherein
A method for producing the iron-rhodium-based alloy magnetic powder described above. 13. The iron-rhodium-based alloy magnetic powder according to claim 10, wherein the precipitate is subjected to a heat treatment to form an oxide containing iron and rhodium, and then reduced by heating. Manufacturing method. 14. The method for producing an iron-rhodium alloy magnetic powder according to claim 10, wherein a heat treatment is performed in a non-oxidizing atmosphere after the heat reduction. 15. A magnetic recording medium provided with a magnetic layer containing a magnetic powder and a binder on a magnetic support, wherein the magnetic powder contains iron and rhodium at least as constituent elements and has a temperature of 30 ° C. to 200 ° C. A magnetic recording medium characterized in that the saturation magnetization changes due to magnetic transition in the range. 16. The magnetic powder comprises iron and rhodium as main constituent elements and further contains at least one element selected from ruthenium, palladium, iridium, platinum and osmium in a molar ratio of 0.1 to rhodium. A magnetic recording medium containing 10% to 10%, and having a saturation magnetization change due to magnetic transition in a temperature range of 30 ° C to 200 ° C. 17. The magnetic method according to claim 15, wherein in the step of raising the temperature above the magnetic transition temperature and then lowering the temperature below the temperature at which the magnetic transition occurs, a change in the saturation magnetization with respect to the temperature indicates hysteresis. recoding media. 18. A magnetic recording medium in which a magnetic layer containing an iron-rhodium alloy powder containing at least iron and rhodium as constituent elements is formed on a non-magnetic support, the saturation magnetization changes due to magnetic transition by heating. Utilizing that, information is recorded by changing the saturation magnetization of the medium using an element having a function of generating heat, and the information is recorded by reading the change in the saturation magnetization using a magnetic head. A recording and reproducing method characterized by reproducing reproduced information. 19. The recording / reproducing method according to claim 18, wherein the element having a function of generating heat is a thermal head for printing. 20. The recording / reproducing method according to claim 18, wherein the magnetic head for reproducing information is a magnetic head having a bias magnetic field applying function. 21. A magnetic recording medium in which a magnetic layer containing an iron-rhodium-based alloy powder containing at least iron and rhodium as constituent elements is formed on a nonmagnetic support, the saturation magnetization changes due to magnetic transition by heating. Utilizing that, information is recorded by changing the saturation magnetization amount of the medium using an element having a function of generating heat, and by reading the change amount of the saturation magnetization amount using a magnetic head, A magnetic recording medium for reproducing recorded information, wherein the information to be recorded and reproduced is barcode information. 22. In a magnetic recording medium in which a magnetic layer containing an iron-rhodium-based alloy powder containing at least rhodium as a constituent element is formed on a non-magnetic support, a change in saturation magnetization due to magnetic transition caused by heating is obtained. The information is recorded by changing the saturation magnetization of the medium using an element having a function of generating heat by utilizing the element, and the information is recorded by reading the change in the saturation magnetization using a magnetic head. Character patterns,
A magnetic recording medium characterized in that information that can be visually identified, such as a picture, is directly recorded using an element having a function of generating heat. 23. A magnetic recording medium in which a magnetic layer containing an iron-rhodium-based alloy powder containing rhodium as at least a constituent element is formed on a non-magnetic support, the change in saturation magnetization due to magnetic transition caused by heating. The information is recorded by changing the saturation magnetization of the medium using an element having a function of generating heat by utilizing the element, and the information is recorded by reading the change in the saturation magnetization using a magnetic head. A magnetic recording medium for reproducing information which is provided with a thermosensitive printing layer for recording the same information as the information recorded on the magnetic recording medium.