JPH03116802A - Magnetic material and method of manufac- turing the same - Google Patents

Abstract

PURPOSE: To improve magnetic or magneto-optical characteristics by applying a heat treatment to a gap spinel type ferrite under the influence of a magnetic field and causing a directional array phenomenon. CONSTITUTION: The gap spinel ferrite for causing the phenomenon of directional array is mainly a spinel ferrite containing at least one kind of the oxide of a metal such as zinc in addition to iron trioxide and cobalt oxide. Such a spinel ferrite is used to make at least one operation comprising heating a raw material compound to the formation temperature of the directional array slightly lower than a stipulated temperature, and after the raw material is maintained at a low temperature for a sufficient period capable of forming the directional array, it is cooled to a room temperature. In this case, the stipulated temperature is a temperature corresponding to the maximum value of the change curve of magnetic or optical characteristics selected from a coercive field, residual magnetization, the coercive field of the residual magnetization, the width of a hysteresis loop, Faraday rotation and Kerr rotation. Thus, the improved magnetic and/or magneto-optical characteristics with less change at a using temperature are secured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has an optimized and stabilized magnetic property.
Cavity spinel type ferrite (1acunarspine
Concerning materials for the structure of l ferrite), their production, and their use in the field of magnetic recording or magneto-optical recording.In fact, in the field of materials used for high-density magnetic recording, acicular It is known that powders of ferromagnetic metal oxides in the form of particles are mainly used. The desired properties of these materials are mainly due to the coercive field, which changes only slightly with the temperature of use.
field), high residual magnetization/saturation magnetization ratio (calb
Magnetic oxides of the air gap spinel ferrite type (substituted sesquioxides) with low magnetostriction and optionally containing glaze dopants have been particularly investigated.

A large number of substitution elements that have been proposed so far (substit-
uent) and/or cobalt as a dopant.

Chromium, zinc, L nickel, manganese, cadmium, alkali metals and/or alkaline earth metals.

Examples include lead, silicon, phosphorus, and boron.

Iron sesquioxide Fe2O3 has a void spinel crystal structure.

Acicular particles of iron sesquioxide can be produced by known methods from a variety of compounds.

The first method, which is the object of a number of variants, consists in the production of α-water, which can be obtained in the form of acicular crystal grains by the action of sodium hydroxide on a solution of ferrous sulfate in an oxidizing atmosphere. Iron oxide (iron a'-oxyhydroxide) (
In other words, it mainly starts from goethite). Thus, colloidal particles of goethite are obtained,
This can be used to grow crystals with large dimensions. When this crystal is dehydrated, hematite (non-magnetic α-Fe203) is obtained. 300 hematite
By reduction with hydrogen at temperatures higher than 0.degree. C.), magnetite particles Fe3O4 with a spinel-type structure are obtained. Finally, by oxidizing magnetite, r
-Fe2es particles are obtained; in this case, by considering the oxidation of ferrous to ferric iron, the spinel-type structure is retained, but voids (1acuna) are formed. Throughout these reactions, the acicular shape of the particles is maintained.

The second method consists of treating ferrous chloride with a base in an oxidizing atmosphere and using as starting material r-iron hydroxide (lepidocrocite) obtained in the form of K-precipitation. By dehydrating 0 rebidochlorite at moderate temperatures, r -Fe2O,5 particles are obtained, which can be obtained by partial exchange of 0 iron, which can be acicular under certain conditions, with various gold JIIK. modified or
Various doping agents are added to the surface or inside of the particles.
Magnetite particles and/or r-Fe2O3 particles modified by the addition of a high valence agent have also been described in the literature. When metal cations with high valence are introduced, the modified magnetite has a spinel-type structure. , which may partially have voids. However, for convenience, in the present invention, the substituted magnetite is 1 non-9-pore spinel ferrite # (''non-1 acu
nar, 5pinel ferrite'')
Modified 7-Fe2O3, i.e. particles based on iron sesquioxide with iron ions and some of the voids replaced by other metal cations, are compounds of ferrite W. Zero-void spinel ferrite is a compound of r-Fe205. A solid solution of ferrite, which when the substituent is divalent, M
It is believed to be OFe203 type.

r -Fe2O3 crystal system (non-magnetic) α-Fe20B
Substituent ions have been introduced into the crystal network structure in order to increase the transition temperature to By the presence of , it is finally possible to perform heat treatment at a higher temperature without reducing the magnetism.

For example, by adding salts of chromium, cobalt, nickel, zinc, etc. to the raw material ferrous acid in the first method described above, or similarly, by adding various salts (for example, salts of alkaline earth metals, silicate By adding salts, phosphates) to goethite, such magnetite particles and/or modified r
-Fe20B particles can be obtained; the desired objective is to improve the magnetism, texture, size and shape of the particles and the magnetism resulting from the particles. - If various dopants are added to the magnetite immediately after production. Also, after carrying out the oxidation step, modified void spinel ferrite particles can be obtained.

Particles of substituted magnetite and/or substituted r-Fe2O3 (void spinel ferrite) are aerated with a mixture of organic acid salts (e.g. acetate, oxalate), i.e. a mixture of iron salts and salts of metals used as substitutes. It can also be obtained by decomposition in The manufacturing process is similar to the method using goethite. ＠The oxide produced by the decomposition of organic acid salts is reduced to convert the α-1'6205 type structure into a spinel type structure (substituted magnetite) K◎
An oxidation is then carried out to finally obtain particles of substituted r-Fe2O3 with a void spinel-type structure. Various variants of this method are described in the literature: for example French Patent No. 2,180,575 and See specification No. 2,587,990.

Furthermore, other substituents or dopants may be added to the substituted magnetite before the final oxidation. Substituent oxides for glazes described in the literature include those containing cobalt; are of most interest for magnetic recording purposes. Cobalt-modified spinel ferrites can be prepared by co-precipitation of iron and cobalt salts (and optionally salts of other cations) used as starting materials @ in the final product, cobalt ions are present in spinel ferrites. Irregularly distributed in the mesh (internal doping (vglumedopi)
ng) ). The nine particles obtained have an improved coercive field. However, for the oxides obtained by internal doping, the remanent magnetization changes significantly at temperatures υ slightly above ambient temperature, which makes it difficult to use the above oxides. For this reason, in the field of magnetic recording, particles whose surfaces are doped with cobalt are used, and by using such particles, the above-mentioned results can be achieved. The drawbacks are reduced ◇ For example, void spinel ferrite can be treated with cobalt in a basic medium at intermediate temperatures.
The coercive field is thus increased and the temperature dependence is smaller than for volume-doped particles. However, the table shows that cobalt has the disadvantage of increasing magnetostriction even when it is present on the surface.Moreover, cobalt ions distributed by surface doping tend to migrate into the interior of the particle over time. A certain method described below also uses ferrous ions as a replacement element.
In order to avoid complete oxidation of the ferrous ions of the zero intermediate magnetite that could introduce n), during the final oxidation step,
It is sufficient to limit the consumption of oxygen by carrying out the oxidation at low temperatures or by adjusting the composition of the oxidizing atmosphere.

The presence of ferrous ions in the final product is of interest because ferrous ions are cheaper replacement elements with positive magnetostriction coefficients.
Ferrous ions can be primarily combined with cobalt, which has a negative magnetostriction coefficient. In a common method, the introduction of a doping agent, of which a number are known, is used to transform the dopant into a void spinel ferrite precursor. By adding the inside of the particle (vo
This can be done by introducing %C into the grain surface or by adding donoplasts to the magnetite precursor or to the voided spinel ferrite itself.

In the field of particles used for magnetic recording, improvements in magnetic properties are mainly achieved by adjusting various heat treatment conditions.
Reduction in the amount of cobalt and texture of the particles
Research is actually being carried out with the aim of improving the structure and morphology; for example, the French patent 2
, 578,990 Reference 0 Until now, it has been experimentally difficult to determine the heat treatment conditions for yuzu along with particle preparation.
◇ In the field of magneto-optical recording, magnetic materials deposited on a support A thin layer of is used. In a magneto-optical recording device, the polarization plane of light produced by a magnetic material, by transmission [2 Faraday effect] or by reflection [Kerr effect] is used.
) rotation is known to be durable. The magnetic properties of air-gap spinel disk ferrites make the material interesting as a magneto-optical recording material for gripping in the form of thin layers. Again, magnetic and/or optical.

It is important to make the properties suitable and to stabilize these properties.
Regarding current materials, this material has been improved by undergoing a heat treatment that systematically optimizes and stabilizes its magnetic and/or optical properties, resulting in less variation at operating temperatures. It has magnetic and/or magneto-optical properties.

In fact, certain types of air-gap spinel ferrites are usually subjected to moderate heat treatment, resulting in localized electronic or cationic structural rearrangements under the influence of temperature and/or magnetic fields.
directional order known to be related to r rangement
) phenomena such as induction appear in a certain temperature range, and this is due to certain magnetic or optical parameters, such as coercive field, remanent magnetization, coercive field of remanent magnetization, heat δ width of the telesis ring
e), Faraday rotation
on ) or Kerr rotation
indicated by an increase in The results of the study on the change in one of the above parameters, fixed #1 at ambient temperature, when the processing temperature of the sample is changed, show that the difference in these parameters (a) at a certain temperature where directional alignment actually occurs
mplitude) increased, in some cases significantly.

In the following, the phenomena and methods underlying the invention will be explained with reference to coercive fields, but it should be understood that any of the parameters mentioned above can be used as a criterion for the appearance of directional alignments. It is.

Directional alignment (the theory behind this is explained by Neel) has been the subject of numerous studies.Whether a given material exhibits directional alignment or not. The phenomenon of directional alignment cannot be measured in advance at temperatures where it will not disappear.
(domain) acicular particles, nor have they been observed for oxides used in magneto-optical recording.

During the appearance of the finger alignment due to heating, the coercive field (or any one parameter selected from the parameters listed above) increases as the humidity temperature increases, passes through a maximum value, and then increases at the above maximum value.・This decreasing line was formed acquiredly (aqui
red) directional array is thermally agitated (thermal a
gitation)

On cooling, the temperature region corresponding to the directional array (on heating) is the formation region of the directional array), and sagging is indicated by an increase in the magnetic or optical properties to a maximum value), but when cooling The directional alignment is maintained while C is being carried out.
The constant values of the magnetic and optical properties are substantially constant;
It is equal to the maximum value corresponding to the temperature range during heating mentioned above.

The results of systematic studies on heat treatment have shown that, in some cases, different bands of directional arrangement appear at different temperatures. According to the method of the present invention, when the magnetic material is cooled,
It is possible to retain the improved magnetic and optical properties associated with each of the directional alignments that appear in the temperature range up to ambient temperature L (@ Furthermore, to reduce the heat treatment time, magnetic or It is also possible to maintain only the processing temperature at which the observed benefits in optical properties are most pronounced.

This method, called ``Induced Anisotropic Heat Scaling Analysis,'' consists of a series of annealing steps at elevated temperatures; each annealing is followed by cooling to ambient temperature, at which point the magnetic Selected magnetic or optical parameters of the material are measured, followed by a fresh annealing at a temperature of:

Thus, curves of the variation of magnetic or optical parameters on the annealing temperature are obtained @ the influence of the heat treatment and temperature range, characteristic of the formation and subsequent destruction of directional arrays, is observed. These temperature ranges include characteristic temperatures that correspond to the maximum values of the change curves of magnetic or optical properties. It was also observed that during passage through the corresponding temperature range, the directional array, which had itself been destroyed, was formed again and retained by the sample, which was cooled to ambient temperature. If there are various regions, the magnetic flux will increase as the directional array is slowly cooled from the highest temperature at which it is formed to ambient temperature as it passes through each of the regions where it is formed. It has also been observed that an advantage or increase in optical properties can be accumulated.

Furthermore, according to the method of the invention, if the directional array appears at a temperature close to ambient temperature, for example between ambient temperature and 80 C or below ambient temperature and 100 C,
Compositions that are difficult to use in practice can be excluded: this is because by carrying out mild heating properties such as the anti-4a field can initially be increased and then reduced. It is very clear that materials with altered (or optical properties) are unsuitable for use in magnetic or magneto-optical recording; the reasons for this are normal or accidental changes that cannot be avoided. This is because the recording will be damaged due to excessive heating.

Furthermore, after measuring the magnetism at ambient temperature, it is possible to slowly cool down to temperatures below the normal ambient temperatures that may be encountered during storage or use of the recording material. By performing measurements of complementary magnetic and/or optical properties at temperatures below nine ambient temperatures, as described above, directional alignment between the conventional ambient temperature and said temperature below ambient temperature is achieved. It is possible to determine whether or not a directional array can appear, and to exclude magnetic materials in which such a directional alignment appears. In practice, by using the magnetic material at such lower temperatures, or by keeping records of the use of the material at such temperatures, during return to ambient temperature or to a higher-than-ambient service temperature. The quality of the recording will deteriorate.

Another advantage of the method of the present invention is that even though the magnetism increases with the formation of the directional array, the magnetostriction does not increase significantly, nor does the thermal deflection of the magnetism increase significantly. There is no such thing.

For a material with a given composition, in the method of the invention, the temperature is first reduced from ambient to the temperature at which the r-α transition occurs, i.e., the spinel-type structure (r-Fe2O
Measure the change in the coercive field (or other selected parameters as described above) measured at ambient temperature after a series of annealing when changing to the α-Fe205 structure of 3). A preliminary process is performed to The annealing temperature interval selected for this preliminary step can be, for example, 10-50''C.

- Once these annealings have been carried out, the temperature and optimum time of the heat treatment that will result in better magnetic performance for the sample under consideration is known. At the same time, it is known whether or not a directional array band exists near ambient temperature; It can be concluded that it is actually inappropriate for use in

After performing this preliminary step only once, the information obtained can be used to maximize magnetic properties of the sample under consideration.
It becomes possible to use it to determine the heat treatment that allows the preparation of the sample: this is, for example, the temperature that corresponds to the maximum value of the curve of variation of the coercive field and at which the formation of directional arrays is observed. (or to the maximum temperature corresponding to the largest increment in the coercive field) followed by slow cooling to zero ambient temperature, carried out by immediate heat treatment followed by slow cooling to ambient temperature. In the place of
A rapid series of cooling can be performed from a temperature corresponding to the maximum value of the effective tζ coercive field to a temperature substantially corresponding to the maximum value of the adjacent coercive field, and then It is particularly advantageous to carry out the staging at a temperature corresponding to the temperature, more precisely slightly lower (for example 5-15° C. lower) than the temperature at which the formed directional array begins to be destroyed. Also, the maximum coercive field is observed and the sample can be rapidly cooled down to ambient temperature.
Moreover, the good magnetic or optical properties obtained are often lost. If the raw material compound is a voided spinel that is non-oxidizable at the maximum annealing temperature (determined as described above), Annealing can be performed in air under an inert atmosphere. If the raw void spinel contains metals that are oxidized at the maximum annealing temperature, annealing is carried out under an inert atmosphere, for example under a nitrogen atmosphere, if it is desired to prevent such oxidation. Substituted magnetite type spinels can also be used as starting compounds, e.g. If the maximum temperature for the appearance of directional alignment, as indicated by the maximum value of the magnetic field, is higher than the oxidation temperature, it may be necessary to perform supplementary heating to the maximum temperature and then cool the sample in the manner described above. Appropriate.

If the maximum temperature for the appearance of directional arrays is lower than the oxidation temperature, it is sufficient to cool the sample after oxidation in the manner described above. It is usually possible to carry out the subsequent heat treatment under an inert atmosphere) or under an inert atmosphere.

It is appropriate to distinguish between the annealing method actually used to produce the final magnetic material; this method is described below. state

The invention thus relates to a magnetic material consisting of a ferrite with a hungry spinel type structure, based on iron sesquioxide, cobalt oxide and at least one other metal oxide and optionally one or more dopants.

This ferrite is produced using the above-mentioned oxide-containing air-gap spinel type ferrite as a raw material in the following manner: from ambient temperature to r→
The annealing temperature is between 10 and 501C, which can be obtained by a variety of methods, including successive annealing at increasing temperatures in the range below the alpha transition temperature, optionally in an applied magnetic field. separated by an interval], while at each selected annealing temperature at least 0.
Observe the process for 5 hours. After each annealing, the composition is cooled to ambient temperature. After each annealing step and subsequent cooling step, the coercive field, the remanent magnetization, the coercive field of the remanent magnetization, the width of the hysteresis ring (3 square
), Faraday rotation and Kell rotation are measured at ambient temperature to obtain a change curve of said properties with respect to annealing temperature. Record the characteristic annealing temperature: this temperature corresponds to the maximum value of said property thus measured; the material in which at least the maximum value of said magnetic or optical property thus measured is observed is Select for an annealing temperature higher than @C but with no maximum between ambient temperature and 80"C. This material is subjected to a final annealing higher than the temperature corresponding to the most ii* maximum of said property. treatment at a temperature of The final annealing temperature is not related to the temperature corresponding to the most significant maximum value of the selected exit air property or optical property, but rather the highest value at which the maximum value of said property is observed. The choice can be made primarily with respect to temperature (when the curve of variation of the selected magnetic or optical property, established as described above, has two maxima corresponding to the acquisition of a coercive field of e.g. X and yOe, respectively, the most significant maximum If X is larger than y, then it corresponds to the obtained X, and if y is larger than X, it corresponds to the obtained y)0. Rather, it can be carried out at slightly lower temperatures, primarily at temperatures lowered by 5-15 C, for example at temperatures at which the directional alignment obtained in the considered temperature range begins to collapse. In some cases, it may be appropriate to carry out a holding step (tagging) at the selected final annealing temperature for the period required for the formation of the directional array. A holding step at a slightly lower temperature can be used as described above. Provided there is no risk of oxidation within the temperature range, various annealings can be carried out in air, or under a virtually inert atmosphere or otherwise. The magnetic material of the present invention can be implemented by adjusting the oxygen content in the case of
．． The present invention can be provided mainly in the form of acicular particles with an acicular ratio of 5 to 10 or, for example, in the form of acicular particles deposited on a support (substrate) having a thickness of 10 to 1100 nm. If the magnetic material is a thin layer, the measurement of the characteristic temperature can be carried out not only on the thin layer but also on acicular particles having the same chemical composition. Thin layers do not themselves have uniaxial anisotropy, unlike acicular particles that have an internal magnetic field. In the case of thin-layer magnetic materials, a preliminary and preliminary treatment under an applied magnetic field, e.g. in the plane of the thin layer or in the perpendicular plane, is appropriate; the applied magnetic field must be essentially constant. Suitably speaking, to produce a thin layer material, for example 100 to 5000 oersteds may be required.
During the temperature holding phase, which is carried out at the highest temperature and during cooling to room temperature or simply at a specific temperature,
Although it is practically appropriate to apply a magnetic field to produce magnetic materials in the form of acicular particles, it is possible to carry out the annealing operation without applying a magnetic field, taking into account the internal magnetic field mentioned above. In the method described above which serves to define the magnetic materials of the present invention, the Ani+IJ song temperature interval is most often on the order of 20'"co, but some of these temperature intervals It is understood that the can always be subsequently narrowed to more accurately measure the characteristic temperature corresponding to the maximum value of the selected magnetic or optical property.
By narrowing this temperature interval, a temperature is found at which the directional array formed by -C1 begins to break down. This is because these two temperatures are so close to each other that they are actually confused. In the present invention, the maximum value of the magnetic or optical property studied while forming the directional array by heating No difference is observed between the temperature corresponding to , and the slightly higher temperature at which the pre-formed directional array begins to collapse during the heating process at a slightly higher temperature.
It is this temperature that is called the characteristic temperature. In a preliminary method of investigating the temperature at which ringing can occur, the duration of the holding phase can be determined for each composition studied by simple steady-state experiments. You can choose between 0.5 and 2 hours.

Temperatures greater than the aforementioned 80°C are preferred, and temperatures at least equal to too''c but less than 150°C are preferred.

As mentioned above, the maximum temperature of the nine annealing studies studied was lower than the r→α transition temperature for the studied compositions;
Generally equal to or even lower than about 600°C.

The void spinel ferrite that causes the above-mentioned phenomenon of directional alignment is mainly composed of oxides of at least one divalent metal selected from zinc, magnesium, cadmium, or iron, in addition to iron sesquioxide and cobalt oxide, and/or Spinel ferrite containing at least one oxide of metals with several valences ◎Metals with several valences such as manganese, % libdenum, copper, vanadium.

Chromium and rare earth metals (yttrium and 2 tanthanides)
Oxides other than iron sesquioxide selected from iron sesquioxide can be present either in the body of the ferrite or on its surface, in the case of predominantly acicular particles.

The magnetic materials of the invention may also contain 111 [or more] conventional dopant agents within the body or on the surface, the dopant being primarily an alkali metal or alkaline earth metal, silicon, in the form of an oxide. ,phosphorus,
This is the boron part.

The oxide constituting the magnetic material of the present invention can be considered to be an ionic compound composed of an 02-anion and a metal cation.

The amount of metal other than iron(1) can be varied depending on the proportion that coexists with the void spinel ferrite structure. The maximum permissible amount can be determined by routine experiments. For example, the amount of cobalt is a metal cation (excluding dopant).
can vary from 1 to 30 molar with respect to the total cations.

The magnetic material of the present invention is a material mainly containing 1 to 5 moles of cobalt. In general, the total amount of divalent metals listed in
can vary from 1 to 30 molti for total cations (excluding dopant).

The total amount of metals with the several valences mentioned above is 1 to 3 for the total cations of metal cations (excluding dopant).
It can change with 0 molti.

In addition, the total amount of mortar of divalent metals, polyvalent metals and cobalt is not greater than 33%.

Rare earths are Eu+Gd, 'rb* Dy, Sn,
The amount of dopant can vary from θ to 5 times tqb of the dopant element with respect to the total weight of the oxide composition, in other words, to express this proportion the corresponding Consider the weight of the element, not the weight of the oxide.

The dopants may be primarily those mentioned above.

The magnetic material of the present invention primarily has a chemical composition (apart from any dopants) of the following formula: Represents at least one cation of a metal, M' being manganese, molybdenum, steel, vanadium.

represents at least one cation of a metal with several valences selected from chromium and rare earth metals;
represents at least one cation of a metal with several valences, y represents a cation of a Co cation, t is a number representing a cation of an O anion greater than 4, and this number is equal to 0.01 or greater, and equal to l or less than 1, w+)(+y sum is equal to or less than 1, preferably t is equal to or less than 0.5 ] The number of O anions greater than 04 in the material arises from the fact that equation (1) practically does not represent a cation void.

The above numbers w, x and y are mainly M, M' and Co
is such that the proportions are the proportions mentioned above.

In the above formula (1), the Fe cation is classified as a divalent cation and not as a polyvalent metal cation. The novelty of the magnetic materials of the invention does not necessarily lie in their chemical composition (indeed, some of these compositions are due to their raw materials). It is pertinent to note that there is an induced anisotropy due to the formed directional arrays (not new from the point of view of chemical composition), and said induced anisotropy can be induced by e.g. coercive fields (or another selected magnetic or optical property) does not increase with heating and remains essentially stable up to a temperature corresponding to a first maximum value of the coercive field, then decreases, and continues to increase as the coercive field increases. It is represented by the fact that the temperature passing corresponds to each maximum value of the magnetic field.

The present invention also relates to a method for producing the above-mentioned magnetic material. This method uses voided or non-voided spinel ferrite as the raw material compound, and the raw material is heated to a formation temperature of the directional array by about 5 to 15° C. lower than a predetermined temperature. carrying out at least one operation consisting of heating the compound and maintaining said raw material at said low temperature for a period sufficient to cause said material to form a corresponding directional array, and bringing the material thus obtained to room temperature. Cooling, default temperature is coercive field, remanent magnetization, remanent magnetization coercive field,
It is understood that the temperature corresponds to the maximum value of the change curve of the magnetic or optical property selected from the width of the hysteresis ring (cal 1 ber), Faraday rotation and Kerr rotation, said change curve being said The maximum value is the most significant maximum value of the curve of change, and when the raw material compound is a non-void spinel ferrite, the raw material compound is preferably converted into a starved spinel ferrite having the desired composition. It is primarily characterized by the fact that it is understood to be heated in an oxidizing atmosphere at a temperature sufficient to cause deformation.

According to a particular embodiment, the method of the invention also provides that the predetermined temperature is the highest temperature corresponding to the maximum value of the magnetic or optical property, and the temperature corresponding to the maximum value of the magnetic or optical property studied. It can be characterized by the fact that the magnetic material is cooled to room temperature, each finding a staging at a lower temperature by about 5-15°C.

It is understood that all annealing temperatures used in the method of the invention are below the r→α transition temperature for the compositions considered. This temperature is determined by magnetic decomposition in °C or α-
[can be easily determined by the appearance of diffraction lines corresponding to Fe205.

When the raw material compound is a void spinel ferrite, the heating rate to a temperature about 5 to 15 degrees C lower than the predetermined temperature is mainly 60 to 200 degrees C/hour, e.g.
0°C/hour.

about 5 to 1 below the temperature corresponding to the most significant maximum value mentioned above.
The cooling rate between the 5"C lower temperature and room temperature can be slow, for example 2 to 10"C/hour, or rapid, for example 150 to 1000C/hour. When it is decided to carry out a holding step in each of the temperature bands corresponding to a maximum value, in addition to that temperature and room temperature, the cooling rate of the two temperatures corresponding to two consecutive maximum value bands is slow. or fast.

In this case, the rapid cooling rate is e.g.
It can be helped by the degree of purity of C/hour. However, the holding step is carried out at a temperature that is lower, for example by 5-15'C, than the temperature corresponding to the respective maximum value.

The duration of the retention phase can be determined in a simple steady-state experiment by determining the period at the end of which the selected magnetic or optical temporality no longer increases with increasing retention phase duration. This period is generally 1 to 20 hours, and 2 to 10 hours.
Most often it is time.

When the raw material compound is a non-void spinel ferrite (substituted magnetite), a preliminary oxidation step is carried out (by heating to an appropriate temperature) to produce a void spinel ferrite with the desired composition, and this heating is generally 6
The oxidation temperature was determined in a steady-state experiment until the desired compound was produced. 0, which is generally between 100 and 600"C.
However, this pre-oxidation step is performed in an oxidizing atmosphere. When it is desirable only to partially oxidize the metal consisting of
For example, if it is desired to retain ferrous iron, the composition of the oxidizing atmosphere and/or the oxidation temperature can be adjusted. In this latter case, if the annealing operation according to the invention uses heating above the selected oxidation temperature, this heating and subsequent cooling is carried out in a neutral atmosphere. In other cases, the heat treatment that is the object of the process of the invention can generally be carried out either in air or under a neutral atmosphere. In cases where heat treatment carried out at a temperature higher than the oxidation temperature at which the voided spinel ferrite composition is obtained may result in undesired complementary oxidation, this annealing carried out at said elevated temperature may be carried out under a neutral atmosphere. It is also a good idea to do this.

When the magnetic material of the present invention is provided in the form of acicular particles,
The raw material particles (substituted magnetite or void spinel ferrite) can be produced by the known methods described at the beginning of the description above.

The magnetic material of the present invention may be zinc, magnesium, cadmium, manganese, or molybdenum.

It is also possible to form a surface layer on r-Fe2O3-based acicular ferrimagnetic particles containing other metal oxides selected from copper, panadium, chromium and rare earth metals.

In order to obtain particles having a core made of r-Fe2O3 and a surface layer made of the magnetic material of the present invention, the particles having this core are placed in a neutral or acidic medium. contact with an aqueous solution of ferrous salts and cobalt salts and at least 1 m of another salt of the aforementioned metals in water such that - of the solution is at least equal to 10 and preferably equal to at least 14. A concentrated solution of an alkaline base, such as sodium oxide, is added and the alkaline solution containing the O core particles is heated, generally from 60 to 100°C, thereby precipitating the hydroxides of the metals present in said solution onto the particles. During the treatment, hydroxide precipitates present on the surface of the particles are transferred into the ferrite layer by dehydration and oxidation.
The relative amounts and proportions of the raw salts are such that the composition of the surface layer thus formed corresponds to the composition of the present invention and the volume of the surface layer represents, for example, 20 to 40 volumes with respect to the volume of the final particles. It can be measured by a simple steady-state experiment. The proportion of cobalt in the raw salt in the surface layer is preferably 1 to 10-
After heat treatment, the ferrite particles are separated by r. filtration and washed to remove excess alkaline base.The washed particles are then subjected to the above treatment to form directional arrays. can. In this case, it is the material on the surface that is likely to form a directional array, considering its composition. During these treatments, some of the metal in the surface layer tends to diffuse toward the core of the particles. The amount of cobalt is determined experimentally in such a way that the amount of cobalt in the core of the particles does not exceed 2.
Preferably, the cobalt eclipse in the core of the particles is measured indirectly by selecting the temperature and duration of the heat treatment such that the thermal induction of the coercive field is less than 30 e/°C for the final product. When the magnetic material is provided in the form of a thin layer deposited on the surface, the material is obtained as follows:
A composition having essentially the composition of the desired substituted magnetite or spinel ferrite forming the raw material in the heat treatment method of the present invention is deposited on a support substrate.

For example, by using as a target a dense composition of void spinel ferrite particles obtained by one of the methods described above and having the desired chemical composition, e.g.
The starting compounds can be deposited onto the support by a riZation process.

Thus a substituted magnetite precursor or a composition having essentially the composition of the desired void spinel ferrite may be deposited on the support.The thin layer then deposited on the support is as described above in the description of the preparation of the granular composition. The thin layer deposited can be subjected to a reduction operation to transform the deposited thin magnetite into a substituted magnetite with a non-voided spinel ferrite structure, and the substituted magnetite can then be transformed into a ferrite with a voided spinel structure by an oxidation treatment as described above for the granular composition. The thin layer deposited thereon can be subjected to the heat treatment method of the invention described above.

Supports are, for example, glass, metals, thermoplastic polymers.

Ceramic, etc. 0 As mentioned above, a preliminary method of measuring the temperature characteristic of thin layers can be carried out on void spinel ferrite particles of the same composition as the thin layer studied.

The conditions for operating the deposition method by cathode powdering can be determined in a conventional manner by routine experiments. This use is also part of the present invention.

The present invention will be illustrated by, but not limited to, the following examples. Influence of Light Oxidation Temperature The raw material particles are composed of substituted magnetite having the following formula: % Formula %.

The raw material particles are obtained as follows: Precipitate the sulfur precursor coo, o6Fe0.79 C2O4' 2H20 in an alcoholic medium.

Mno, t 5 then at a slow heating rate (10°C/hr) to 300″C1 and then at a rapid heating rate (200°C/hr) to 600″C followed by a 0.5 hour hold step before the above. Thermal decomposition of the skeleton.

The obtained decomposition products were heated at 320'C for 1 hour with N2 (10%
) and N2 (90%) and then reduced to 450
Treat at ℃ for 1 hour under N2 (tool) atmosphere.

The obtained ferrite particles are heated in air at various increasing temperatures at a rate of 150°C/hour, each time holding at the selected temperature for 2 hours, and then the particles are heated to 1000°C/hour. The coercive field and residual magnetization are measured each time during cooling to room temperature at a rate of .

The measurement results are shown in Figures 1 and 2. Example 2 Influence of aging stage period The raw material compounds are the same as in Example 1 Two samples of this substituted magnetite were heated at 380"C (heating rate 150℃/ The samples were oxidized in air by heating for 2 hours for the first sample and 6 hours for the second sample.

The following results were obtained: Sample Coercive field (Oe) Residual magnetization (RM)
(ueln/'P)1 1300
412 1365
42 Example 3 Annealing of voided spinel ferrite Particles of voided spinel ferrite were heated by air oxidation of the raw material compound of Example 1, i.e., directly heated to 350° C. in air, held at this temperature in stages for 5 hours, and then rapidly cooled to room temperature. It is prepared by cooling, heating M degree U 150° C./h, cooling rate is 1000′c/h.

The resulting ferrite particles have the following composition: Mn 0.44 COD, 17 Fe2J 904.44, Ha 12.400e and RM 40.2ue
m/f, and 9 RM/MS is 0.73 (However, MS is saturation magnetization). Same as described in Example IK except that the oxidation temperature (350 ° C.
) A series of Ani+IJ song annealing in air at low temperatures was performed on the resulting ferrite grains. The oxidation state of the ferrite compound does not change.

The measurement results of the coercive field and residual magnetization are shown in FIGS. 31 and 4, respectively.

Example 4 The following composition: Mrio, x3Coo, oa Fe2. s* 0ak5
, Hc = 4940e, RM: 40, 2 uem
/f, RM/M8-0.65 void xt nelferrite particles described in Example 3 were used as raw materials, and annealing was performed in the same manner as in Example 9. These 7-2ite particles had the following composition. :N! no, sa coo, o
a 35 substituted magnetite with Fe2.5904
These '2N spinel ferrite particles were annealed under the same conditions as in Example 3. The results obtained after performing this are shown in the following Table 1〇@1 Different T annealing (“C) Hc(Oe) RM
(uern/f) RM/MS20
494 40.2 0.651
00 497 40.1
0.65210 506
40.6 0.66260
551 40.9 0.6
7300 536 40.4
0.66350 473
38.7 0.54 Example 5 The following composition: MflG, 07 COo, 12 Fe2J104.4i
S and Hc=7250c: RM=42.2 uem/f
: The annealing operation was performed in the same manner as described in Example 3 using void spinel ferrite particles having RM/MS = 0.67 as a raw material.◇ These ferrite particles had the following composition: M-n(1 , 07CGo, 12 Fe2.8104 was oxidized at an oxidation temperature of 350° C. (5 hour holding step) and rapidly cooled to room temperature.

Example 3 about these interstitial spinel ferrite particles
The results obtained after annealing under similar conditions are shown in Table 2 below.

← S! Conversion unit CGS: 10e-10"/4πA/m 1 ue+n/P W I Am"/Kf At a temperature lower than that at which void spinel ferrite is obtained by oxidation of substituted magnetite, void spinel ferrite is obtained in this specification. When exhibiting a coercive field peak as defined in , slow cooling allows a significantly larger acquisition of coercive field with respect to rapid cooling. Thus, the following composition (separately from the dopant): "0.
14 Zn0.04 Fe2.8204.41 jO-
02Ba1t o,o5 The voided spinel heptite particles obtained by heating the corresponding substituted magnetite with B2O5 at 310°C for 2 hours in air were
It was cooled at a rate of 7 hours or 5° C./hour, and the coercive fields were 8200e and 9100e, respectively.

Example 7 The same cooling experiments as in Example 6 were carried out on void spinel ferrites with the following formula:
It can also be obtained by oxidizing for 2 hours at 0"C. When rapidly cooled, Hc
w7050e:RM=40. When luem/7 is obtained and slow cooling is performed, Hc =7440e:
RM = 40.6 uecn, zuri got letter 0

[Brief explanation of drawings]

Figure 1 shows the coercive magnetic field (vertical 4111
) and oxidation temperature (horizontal axis);
The figure is a chart showing the relationship between residual magnetization (vertical axis) and oxidation temperature (horizontal axis) of the ferrite particles of the present invention. Figure 3 shows the relationship between the coercive magnetic field (vertical axis) and annealing temperature of the ferrite particles of the present invention. (horizontal axis), and FIG. 4 is a diagram showing the relationship between residual magnetization (vertical axis) and annealing temperature (horizontal axis) of ferrite particles of the present invention.

Claims (15)

[Claims] 1. A magnetic material consisting of a ferrite of the void spinel type based on iron sesquioxide, cobalt oxide and at least one other metal oxide and optionally containing one or more dopants, the ferrite being obtained by annealing, optionally in an applied magnetic field, at temperatures increasing between ambient temperature and temperatures below the r→α transition temperature for said material. the annealing temperatures are separated by intervals of 10-50°C and the process is observed for at least 0.5 hour at each annealing temperature selected; cooling the ferrite composition to ambient temperature; after each annealing and subsequent cooling, the coercive field, remanent magnetization, coercive field of remanent magnetization, hysteresis loop caliber; measuring at least one of the magnetic and/or optical properties selected from Faraday rotation and Kerr rotation at ambient temperature, thereby obtaining a change curve of said property with respect to the annealing temperature; Record the annealing temperature corresponding to the maximum value of the above properties; 80°C
For higher annealing temperatures, select a material with at least one of the maximum values of the magnetic or optical properties thus measured, ignoring the maximum values between ambient temperature and 80 °C; A magnetic material characterized in that: heating the material to a temperature above the temperature corresponding to the most significant maximum of said property; and then cooling said material from said elevated temperature to ambient temperature. 2. Said annealing temperature higher than 80°C is at least equal to 100°C and 10°C above ambient temperature.
2. A material according to claim 1, wherein no maximum is observed between 0<0>C. 3. 2. Material according to claim 1, wherein the rate of slow cooling is between 2 and 10[deg.]C/hour. 4. In addition to the iron sesquioxide and cobalt oxide, it contains at least one divalent metal selected from zinc, magnesium, cadmium, or iron and/or at least one oxide of a multivalent metal. 2. The material of claim 1, wherein the total molar amount of cobalt, divalent metal and polyvalent metal is less than or equal to 33%. 5. 5. The material of claim 4, wherein the total amount of divalent metals is 1 to 30 mol% of the total number of moles of metal cations, not including dopant. 6. 5. Material according to claim 4, wherein the multivalent metal is selected from manganese, molybdenum, copper, panadium, chromium and rare earth metals. 7. 1 . The total amount of polyvalent metals is 1 to 30 mol % of the total number of moles of metal cations, not including dopant. 1 .
Materials listed. 8. 2. The material of claim 1, wherein the amount of cobalt is from 1 to 30 mol% of the total moles of metal cations, without dopants. 9. The following formula: MwM'Co^+^2_yFe^+^3_3_-_w_
-_x_-_yO^-^2_4_+_t (I) [In the formula, M represents at least one cation of a divalent metal selected from zinc, magnesium, cadmium, or iron, and M' represents manganese, molybdenum, copper, panadium, chromium. and at least one cation of a metal with several valences selected from rare earth metals, w represents the number of moles of said cation of a divalent metal, and x represents said cation of a metal with several valences. y represents the number of moles of Co^+^2 cation, t is a number representing the number of moles of O^-^2 anion exceeding 4,
this number is greater than or equal to 0.01, and is less than or equal to 1, and the sum of w+x+y is less than or equal to 1. , the material of claim 1. 10. 2. A material according to claim 1, provided in the form of acicular particles, a surface layer of ferrimagnetic acicular particles or a thin layer deposited on a support. 11. A reactant feedstock consisting of voided or non-voided spinel ferrite is adjusted to a directional array formation temperature of about 5 to 15° C. below the predetermined temperature, and the feedstock is heated to a temperature sufficient to cause the material to form a corresponding directional array. maintaining said low temperature for a period of time and cooling the material thus obtained to room temperature, said predetermined temperature being dependent on the coercive field, the remanent magnetization, the coercive field of the remanent magnetization, the width of the hysteresis ring, the Faraday rotation and the curvature. It is understood to be the temperature corresponding to the maximum value of a curve of change of a magnetic or optical property selected from rotation, said curve of change being established by the method according to claim 1, said maximum value being said heating in an oxidizing atmosphere at a temperature sufficient to transform the reactant stock into a void spinel ferrite of the desired composition when the reactant stock is a non-void spinel ferrite; The method for producing a magnetic material according to claim 1, which is understood to be the same. 12. Said predetermined temperature is the highest temperature corresponding to the maximum value of said magnetic or optical property, and at each temperature corresponding to the maximum value of said magnetic or optical property, about 5 to 15°C. 12. The method of claim 11, wherein the magnetic material is cooled to ambient temperature while observing the process at a lower temperature. 13. Approximately 5-15 below the temperature corresponding to the most significant maximum value
12. The method of claim 11, wherein the cooling rate between a temperature below 0C and ambient temperature or between the maximum temperature and ambient temperature is between 2 and 10C. 14. The cooling from said higher temperature to ambient temperature or between two temperatures corresponding to two successive maximum value regions or between such temperature and ambient temperature is rapid and the step (
12. The method according to claim 11, wherein the staging) is observed in each temperature range corresponding to a maximum value. 15. A magnetic recording and/or magneto-optical recording material comprising the magnetic material according to claim 1.