DE1915358A1 - Magnetic material - Google Patents

Description

Western Electric Company Incorporated Nosbitt, 24 / 25-17-3 / 4

New York, N.Y. 10007 U.S.A.

Magnetic material

The invention relates to permanent magnetic materials, some of which have extremely high coercivity, as well as to a method of making the same. Exemplary materials can have large energy products and are therefore in use cases such as torque drives, loudspeakers, motors and the like, useful in which the magnetic circuit is usually has an air gap.

As described in 38-3 Journal of Applied Physics, page 1001 (March 1967), it has been known for some time that certain intermetallic compounds of many of the lanthanides seen rare earth metals and related elements in powder form have permanent magnetic properties. These compositional materials such as Co _c Y, Co Ce, etc. have extremely high crystalline anisotropy and high coercivities. In fact, coercivities of 9,000 oersteds and higher have been measured on particles small enough to prevent significant domain wall movement (particles on the order of 10 micrometers). While how kl

the cited reference is reported to these materials as For fine-particle permanent magnets are considered promising, attempts have been made to improve the permanent magnetic properties in to maintain solid bodies is unsuccessful.

The invention resides in a variety of permanent magnetic compositions as well as in processes for their production. The compositions according to the invention lie within certain ranges of the system represented by AB (RE), where A stands for iron or cobalt or a mixture thereof, furthermore B stands for copper, nickel or aluminum or mixtures of copper with aluminum or nickel as well as (RE) for the ancient earth samarium or another Rare earths such as gadolinium, praseodymium, cerium, neodymium, holmium or the elements lanthanum and lanthanum, which are completely substituted for this purpose or are added in smaller quantities and are related to the rare earths Yttrium. For the sake of simplicity, all elements of the latter group are referred to here as rare earths and by the symbol (RE) shown.

Certain of these compositions fall on the stoichiometric line between compositions A- (RE) and B- (RE). In these compounds, the stoichiometric relationship of five trivalent cations for each rare earth anion is maintained throughout.

However, this stoichiometric relationship does not follow the usual ionic relationship and therefore implies the existence of related compounds close, which do not have a total of six ions.

Compositions other than the (ABL (RE) stoichiometry) can be made and exhibit magnetic properties comparable to those of the (AB) - (RE) compounds (RE) -B (RE) and A ₁ - (RE) ₀ and B ₁ - (RE) is limited between 20 and 100 % A and 2 to 100% B. The percentages given in this description are all atomic percentages.

In any case, it is component A, cobalt, iron or a cobalt-iron mixture that provides the magnetic properties. Diluting component A with element B reduces the saturation magnetization of the overall compound. The non-magnetic component B is responsible for minimizing or eliminating the domain wall movement, so that increasing amounts lead to increasing coercivity. The highly significant improvements in coercivity thus obtained are one of the surprising features of the invention. Useful improvements result in this respect by the incorporation of component B in amounts greater than 1, 7 atomic percent and less

003868/0753

than 71.5 atomic percent. These values correspond to the molar range from 2 to 80% of component B ₁ calculated as B (RE), where χ is approximately between 5 and 8.5.

Although these compounds are referred to as intermetallic compounds can be, it is perhaps more meaningful to the whole To consider composition as a solid solution. It should be understood, however, that this terminology does not the intention is to denote complete homogeneity. Based rather, on the reported examiner's work and on the general theory of other permanent magnetic materials, it is it is likely that areas of compound A (RE)

are known to be separated by areas of connection B (RE),

to reduce domain wall movement.

The essence of the invention lies in the retention of certain permanent magnetic properties in comparatively massive bodies. While cast blanks (as-cast bodies) show sufficient magnetic properties for many applications, a preferred aspect of the invention is derived from the discovery that heat treatment at low temperature can further improve these properties. Under certain circumstances, an even greater improvement can be achieved by

009888/0753

Λ *

that the cast materials are pulverized and subsequently one be subjected to further treatment. For example, the powdered materials can be oriented in a magnetic field and finally sintered or otherwise fixed in this orientation to get a new solid. Since the cast blank shows the general effects of single domain particles, it is not necessary to rait the previously required powder materials to produce small grain size.

In the following the invention is described with reference to the drawing; show it:

1 shows the ternary composition diagram for the AB-RE system for describing the compositions according to the invention, with A standing for cobalt or iron or a mixture thereof, furthermore B for copper, nickel or aluminum or mixtures of copper with nickel or aluminum and finally RE for at least one element from the group samarium, cerium, gadolinium, praseodyn, lanthanum, yttrium, neodymium and holmium,

Fig. 2 shows the dependence of the coercivity (in Oereted) on the atomic ratio of B to A in the general formula (AB) ₅ (KE) to illustrate the relationship between the-

009m / 0? S2

sen both parameters for cast blanks and also for subsequently heat-treated material in the composition system along the pseudo-binary line A (RE) -B ₅ (RE),
3 shows the dependence of the saturation magnetization BH

(in Gauss) of the atomic ratio of B to A in the formula (AB) (RE) to show the relationship between these two parameters for two compositions with different rare earths, Fig. 4 shows the dependence of the coercivity (in Oersted) on the atomic ratio of B to A in the formula (AB) _DR (RE) for

ο. ο

Representation of the relationship between these two parameters for compositions _{lying along the pseudo binary line A Q} - (RE) -B ₀ ARE) , and

ο.Ο ο. Ο

5 shows the dependence of the saturation mapping BH (in Gauss) on the atomic ratio of A to B in the general formula (AB) _{0 C} (RE) to illustrate the relationship

o. o

between these two parameters for compositions lying along the pseudo binary line A ₀ - (RE) -B _{8 5} (RE).

The effective compositions are best based on the

000306/0753

1315358

described ternary diagram of Figure 1; there are those who are interested Compositions of those in the daj shaded area Z fall and the relationship

(AB) (RE)

meet, where χ goes from about 5 to about 8.5. The shaded area Z can be defined in the composition by its boundary lines. These lines intersect in the with a, b, c and d designated points of the following composition

a: 18% A.
71.5% B

10.5 % Rare Earth b: 16, 7
66.6
16.7 %
%
QJ A.
B.
Rare Earth c: 81.6
1.7
16.7 Q / A.
B.
Rare Earth d: 87.7
1.8
10.5 % A.
B.
Rare Earth

As indicated above, component A, which is the magnetic component, is cobalt and / or iron. The way it looks is cobalt preferable because the resulting compounds have higher coercivities. While the coercivities are more ferrous Materials according to the invention are improved, they are lower than the cobalt-containing compounds. Nonetheless

009886/0753

there may be occasions in which a partial or complete Substitution of the cobalt by iron is preferred. This is due to the fact that the saturation values increase. By analogy with other magnetic materials, it was observed that the highest saturation values for the same iron and cobalt atomic proportions are obtained. A desired sub-area is a maximum of about 60 atomic percent iron. 2 atomic percent iron can be regarded as a preferred lower limit. These Limits are prescribed on the basis that the partial

Substitution takes place to increase the saturation magnetization. The incorporation of extremely small amounts of iron increases the saturation, although an appreciable increase is only achieved when the specified lower limit is used. The use of amounts well above the maximum value does not provide a further increase in saturation and, at the same time, a decrease in the coercivity associated with the cobalt-containing compound.

Component B of the system is copper, aluminum or nickel, or mixtures of copper with aluminum and nickel. The best results obtained were based on copper-containing compounds, though Much of the magnetic improvement retained

if the copper completely or by aluminum and / or nickel is partially substituted. It has been found that the atomic percentages of the elements copper, nickel and / or aluminum are desirable should be between 2 atomic percent and 80 atomic percent, based on the total number of atoms of these elements together with cobalt and / or iron.

From the above description, it can be seen that it is desirable is as little as possible of a copper, nickel and / or Make use of aluminum compound as this little magnetic contribution to the final composition at normal operating temperatures supplies. It is characteristic that there is an increasing substitution of the cobalt and / or iron containing compounds first generate an increasing and finally a decreasing coercivity can, while at the same time a constantly decreasing saturation results. This behavior is shown in the drawings. Based on these observations and assuming that a high coercivity is combined with a high energy product is desirable, it is possible to have a more preferable composition range to be defined as that in which the ratio of U to A reaches the range of about 0.2 to about 1.5. Of course others can. Considerations based on specific

Device requirements are based on the use of compositions suggest outside this preferred area. While 8, 5 formula units for components A and B as a convenient Maximum have been described, it can be seen that these mixtures are not stoichiometric and that this value is somewhat can be exceeded while still obtaining the unexpected benefits of the invention.

The final choice of the area for the incorporation of the non-magnetic compound cation depends to a certain extent on the processing conditions. Increasing cooling rate from the reaction temperature leads to an increasing coercivity and thus gives rise to the assumption that a high temperature phase precipitation is present in the final composition at least with respect to one or the other of the two compounds. Also can währerid dif * given wide limits in all affected systems are desirable give rise to peak values of coercivity in a slightly modified preferred _EJereich> certain Zusainmensetzungs- or processing excessive deviations.

The invention is described as far as possible. It is based on the Maintaining permaneiitmagmitiHchor properties in bodies that

are much larger than single domain particles. This effect can ι. ·; Bodies are retained, of a number of compositional components contains. For example, some oriented samples have been made by pulverizing solid materials (Particle size 5Ou or more), by embedding them in a matrix, e.g. in a wax, and by orienting them in a created field. It is clear that the relative amount of matrix material can be extremely large. In principle, permanent magnetic effects can even then be retained in bodies in which the particles are separated from one another by distances that are orders of magnitude larger than the particle size.

While certain additives are used to modify certain of the unnoticed ones Properties that can be incorporated, the most important additives with regard to coercivity or saturation have already been described been. Other ingredients can include elements such as iron to increase permeability and elements such as vanadium Improvement of mechanical properties, such as processability, lock in. Unintentional additions are generally insignificant in amounts in which they correspond to customary process deviations to be built in. Such inclusions, which can total one or a few percent, also

009886/0753

significantly larger inclusions have little effect on the Structure of the compound making the magnetic contribution.

However, since a high energy product is often desirable, and since non-magnetic inclusions, similar to dilution, lower this value, a preferred composition range is no more than 10% by weight of additional ingredients present in solution in either or both of the mixed compounds. However, this preferred limit is not to be interpreted as a restriction with regard to the presence of additional phasers, for example a wax matrix.

In some of the earlier work on mixed compounds of the Materials containing transition metals are held instead of mixed metals a pure rare earth has been used. A material in which cerium is predominant costs only a few dollars per pound compared to the at least one order of magnitude higher costs for individual rare earths. These and other types of mischmetal can be used in preparing the compositions of the invention.

It is known from earlier work that the role of the electron orbits of the rare earths cerium, samarium, praseodymium and neodymium

009886/0753

make the permanent magnet less antiferromagnetic. There In general, the invention enables suitably high coercivities for each of the compositions in question resulting increase in satiety, and consequently in energy product to the fact that these four anions are preferred.

processing

It is usually desirable to prepare the solid solution according to a method which is rapid after the reaction Includes cooling process. It was observed that the coercivity with increasing cooling speed increases, namely at least in the temperature range down to barunter to about 600 C. It

there are no experimentally determined criteria for this relationship. Materials that melt from a melting point of around 1600 ° C to 600 ° C Cooling for 15 minutes showed coercivities of 6000 oersted compared to 13000 oersted for the same and identical processed composition, but with cooling over the same temperature interval within about 1 millisecond away. It is always considered desirable to have a cooling rate of at least 1000 ° per minute, and this value is considered to be a preferred limit for this process step considered.

ΠΛ ÖD ö ß / nTO

Ίο

One metallurgical method apparently useful in making the inventive materials is arc melting, and some of the results reported here were obtained with samples made by this method. Samples were also prepared by solidification, floating zone melting, and rapid quenching from the liquid state. Other methods, such as allowing the cooling indicated above, are satisfactory. The only additional requirement for processing is that reactive atmospheric constituents must be excluded, since, for example, the metallic elements of the rare earths form hydrides, nitrides and oxides. For this reason, hydrogen should
Nitrogen and oxygen are largely excluded. It has been found convenient to melt under an inert atmosphere,
7 '. B. argon.

Briefly, the arc melting method is as follows: The amounts of the required according to the desired stoichiometry
elementary material in are weighed and melted. the
The apparatus used consists of a water-cooled copper heart. with a hemispherical cavity with a diameter of 1.9 cm. A second, stable electrode, which is also water-cooled and is for example made of tungsten, is located some

QO988S / Q753

Millimeters away from the monitoring of the reactants. An arc is ignited with the help of a high frequency current (250 amps or more) and with sufficient DC voltage maintained to create a melt. For a batch totaling 30 grams, 30 volts ran at a distance from 13 mm to a current of about 500 amps, which was sufficient to obtain a melt in about 30 seconds. The cooling from the melting temperature of 1600 C to about 600 C is achieved within about 25 seconds by switching off the Oven performance reached.

It has been found that a heat treatment at low temperatures zv to a considerable increase in coercivity. While some improvements in coercivity were obtained by heating up to 300 ° C for up to an hour, peak coercivities were generally only obtained with heating at 300 ° C for at least about 4 hours. Heat treatment at higher temperatures leads to the same improvement in shorter times. The heat treatment can be carried out at temperatures up to about 7C0 ° C. The heat treatment time at this elevated temperature, which is required to obtain a measurable improvement in the coercivity, is in

On the order of 30 seconds. The peak coercivity becomes reached in about 30 minutes. Corresponding optimal times at 400 C and 500 ° C are around 4 and 1 hour, respectively.

The mechanism involved in heat treatment is not yet fully understood. It seems to be consistent with the "experimental results." to cover if one assumes a certain degree of a phase division or a kr istallogr aphis che, n order.

While the invention is based on the retention of permanent magnetic Properties in solids of the material is based and thus the need for pulverization to single-domain particle size avoids, it may nonetheless be desirable pulverize the cast or heat-treated blank. One reason for pulverizing is to allow orientation, which can be carried out at temperatures which exceed the Curie temperature (generally of the order of a few one hundred C). In contrast to the well-known single connection material the particles oriented in this way can subsequently be sintered in order to obtain a solid again. Since the Magnetic connection is inherently anisotropic, this additional process step can lead to a notable increase

009886/0753

of coercivity. The degree of orientation depends of course on the extent to which the single-domain particle sizes can be achieved. While it's usually not expensive. Powders with a grain size up to 10u, like this one was previously required to produce, it may be desirable to pulverize down to about 50 11. Such powdered samples steller, an advance compared to the known single compound samples in that they can be sintered without losing their permanent magnetic properties.

properties

The coercivity and saturation magnetization, B-H, for compounds of the general formula (AB) - (RE), where the ratio of B to A changes from zero to four, are in Figures 2 and 3, respectively shown. The coercivity and the saturation magnetization, B-H, for compounds of the general formula (AB). - (RE), where the

ο, ο

The ratio of B to A changes from zero to above 5 /3.5, and is shown in FIGS. 4 and 5, respectively. In each case two curves are shown. In FIGS. 2 and 4, curves 2 and 6 describe the coercivity for the compositions as they are cast , whereas curves 1 and 5 show the results after the previous

reproduce the heat treatment or aging procedure described above. The improvement achieved as a result of the heat treatment is evident.

Figures 3 and 5 also show two curves. Curves 3 and 7 show the properties of compounds, the samarium as the rare earths, while curves 4 and 8 show the properties of compounds containing cerium as the Rare earth included. ■;,

The data provides the properties for the boundary compositions in shaded area Z of Figure 1 and provides a solid basis for predicting the properties of the included compositions. The coercivity values of other exemplary compositions in question are given in the table below.

Tabel

Material H Oersted (as melted)

■. Ι ι »- C

Co ₄ Cu ₁ .Co 7500

CoXu, _K Sm 4500
4 1.5

Co * _ft .Cu, «nSM 2300 (3500 after aging) 5.07 1. 17 \

Co.- ,. Cu, -Ce 1400 (4800 after aging) 5.25 1.5

/ i

For many purposes, the value of a permanent magnetic material becomes measured on the basis of its energy product. This value

'which in a certain sense is a measure of the amount of energy that is

Air gap can be accommodated is usually taken as the product of magnetization B and coercivity H at the knee the hysteresis curve in the second quadrant. For the materials of the invention where the coercivity is typically much greater as the magnetization is, the energy product can be taken

are displayed as B ·· ++ / *. » where B is the saturation magnetization. satty 4 full

Typical values for preferred compositions within the scope of the invention are above 10 Oersted Gauss. Certain of the materials showed measured products of 9 million.

use cases

The materials of the invention are mainly characterized by their large coercivity values. These lay the use in magnetic circuits with an air gap close. The applications include, for example, magnetic bearings, DC motors and torque drives. In contrast to the competing commercially available Alnico Mafcerialien, the compositions according to the invention take the form of bodies

009886/0753

2o

with relatively short dimensions in the direction of magnetization. To compensate for the sometimes higher saturation values available in other materials, the magnetic Elements have larger cross-sectional areas perpendicular to the direction of magnetization. In contrast, must the best known commercially available materials, while they can take the form of small section elements, im generally be of greater length to allow the anisotropy through Increase shape effect.

The invention has been explained on the basis of a number of exemplary embodiments. Certain changes in the composition and processing have been described, others are evident. The invention is based on the retention of individual domains » particle properties in solid bodies of the specified compositions. This property is the inclusion of Attributed to copper, nickel and / or aluminum in any of the specified cobalt and / or iron containing compounds.

009886/0753

Claims (13)

patent claims 1. Magnetic material with a component (A) that is at least is an element selected from the group consisting of cobalt and iron, and having a component (RE) which is at least one selected from the group consisting of samarium, cerium, gadolinium, praseodymium, lanthanum, yttrium, neodymium and holmium Element is characterized in that the material furthermore has a component (B) which consists of at least one of the copper j Nickel and aluminum group consisting of selected element is that the material has the general formula (AB) (RE), where χ is between 5 and about 8.5, and that the composition is within a range in a tervical diagram that bounded by the lines drawn between the following points is: a: 18 ° _t 71.5 ·, 10.5 °, b: 16.7 ° j 63.6 ° i 16.7 ° i c: 81.6? 1.7? 16.7 7 d: 87.7 7 1.8 f 10.5 ^ % A fo B to (RE) % A ¹ O B Ό (RE) ^f o A Ό Β i (RE) ο A ό Β Ό (RE) 2. Material according to claim 1, characterized in that (B) is present in amounts between 2 atomic percent and 80 atomic percent, based on the total amount of (A) and (B). 3. Material according to claim 1 or 2, characterized in that copper is present as (B) . 4. Material according to claim 1, 2 or 3, characterized in that cobalt containing up to 60 atomic percent iron is present as (A). 5. Material according to one of claims 1 to 4, characterized in that (RE) is at least 50 atomic percent cerium. 6. Material according to one of claims 1 to 4, characterized in that (RE) is at least 50 atomic percent samarium. 7. A method for producing a permanent magnetic material according to any one of the preceding claims, by mixing the Reaction partners which lead to a composition which at least one from the group consisting of cobalt and Elsen selected item, along with at least one of the selected items Samarium, cerium, gadolinium, praseodymium, lanthanum, yttrium, neodymium and holmium containing selected element, by heating to the melting point and by cooling, characterized by additional admixture of a material »to the reactants, which is at least one of the copper, nickel and aluminum, and that the composition of the reactants is selected so that the final composition can be represented by the approximate formula (AB) (RE), where χ between 6 and Ji about 8, 5 lies. 8. The method according to claim 7, characterized in that the Cooling in the temperature range from about 1600 ° C to about 600 ° C takes place within a maximum of 15 minutes. 9. The method according to claim 7 or 8, characterized by holding the composition at a temperature of 300 ° C to 700 C for a period of 4 hours to 30 seconds, the longer times corresponding to the lower temperatures. 10. The method according to any one of claims 7 to 9, characterized by pulverizing the resulting composition and 15358 by subsequent magnetic orientation of the powder. 11. The method according to claim 10, characterized in that the oriented powder particles are fixed in a relative position. 12.. Method according to Claim 11, characterized in that d * ea dl · The relative length is fixed by sintering. 13. The method according to claim 11, characterized in that, dano dl · oriented particles are frozen in a matrix. 009886/0753