US2964793A - Method of making permanent magnets - Google Patents

Description

Dec. 20, 1960 w. s. BLUME, JR 2,954,793

. METHOD OF MAKING PERMANENT MAGNETS Filed Nov. 13, 1957 INVENTOR.

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wgd 5 United States Patent METHOD OF MAKING PERMANENT MAGNETS Walter S. Blume, Jr., Cincinnati, Ohio, assignor to Leylong: Corporation, Cincinnati, Ohio, a corporation of Filed Nov. 13, 1957, Ser. No. 696,164

Claims. (Cl. 18-475) This invention relates to a method of making permanent magnets and is directed particularly to magnetically anisotropic permanent magnets made of ferritic compositions.

The principal objective of the invention has been to provide a method of making permanent magnets havingv 'For-that reason the conventional mode of fabrication has been to cast'the molten alloy composition'into a mold conforming to the ultimate shape desired. Where dimensional accuracy is requisite, the casting is then ground to form or size.- The cost of this mode of fabrication obviously is appreciable, the surface finish of the unground casting is generally poor, and there is considerable variation from piece to piece in all unground dimensions.

7 More recently, it has been shown, as in Gorter et al. US. Patent 2,762,778 dated September 11, 1956, that barium, strontium, or lead ferrite can be made to possess desirable permanent magnet properties by comprising particles thereof and sintering the compressed particle mass. The best technique known heretofore for preparing such non-metallic or ceramic products involves addition of a binder solution to the powder before compression to impart temporary physical stability thereto sufiicient to permit the mass to be'handled and conveyed to the sintering furnace. During sintering, of course, the binder burns away. To improve the magnetic properties, the particles are subjected to a magnetic field while they are dispersed in the binder liquid'prior to their compression and sintering. Unless the sintering is performed very carefully, undue crystal growth occurs which reduces coercivity and thereby counteracts the improvement of magnetic qualities which the sintering is intended to provide.

-Machinable magnets have been produced by the compression or injection molding of mixtures of subdivided magnetic material and plastic, but the superior properties peculiar to ultrafine anisotropic materials cannot be utilized in such procedure and the magnets inevitably display low energy products for that reason.

Permanent magnets of the ferrite class potentially are less expensive than metal alloys such as Alnico because the raw materials from which the ferrites are made are much more abundant and readily available. However, the ferrites are of a crystalline refractory nature to begin with, and the sintering which is required for the production of permanent magnets of good quality therefrom renders variety of shapes as is the casting method. The present invention is predicated on the discovery and determination that readily machinable permanent magnets of excellent quality can be made by dispersing small particles of an anisotropic permanent magnet material in a liquid medium having a viscosity not substantially higher than that of water, subjecting the dispersion to a magnetic field to align the particles so that their preferred magnetic axes are. parallel, separating the liquid medium from theparticles and causinga normally solid matrix material to solidify around the particles to bind the particles in their aligned positions.

The permanent magnets of the present invention are magnetically anisotropic materials displaying permanent magnet properties comparable to or exceeding the ferro magnetic materials which have previously been known, but they also possess qualities of machinability, workability, or cutability, which make them amenable to fabrication in simple or intricate shapes, as desired, by the use of ordinary cutting tools or instrumentalities as distinguished from the grinding to which past products have been limited. The products of the invention preferably preparation of readily machinable permanent magnets which the past materials have been deficient, and the finished products are limited as to shape only by the nominal costs involved in the production machining of bulk solids.

It is well known in the art that modern permanent or a so-called hard magnetic material is distinguished by high the resultant products too hard to be cut or shaped by ordinary methods of machining and undesirably brittlef Sometimes Alnico type materials are also produce'd in similar manner. However, except by the use of expensive compression forming dies, the pressingand 'sint erin g technique is'not even as well suited to'theproductionof a maximum energy product, for example BH max value of approximately starting from 0.5 X 10 gauss-oersteds, high Where the permanent magnet is comprised of an aggregate of finely divided consolidated particles rather than an undivided solid, it is also known that if the particles possess a high degree coercive force Hc, and high remanence.

of anisotrophy, superior properties are conferred bymagaligned magnetically with respect to one another.

or because of inter-particle interference or both.

In accordance with this invention, magnetic alignment of the particles and the property of machinabilitv are ob; tainedin a permanent magnet of the consolidated powde'r type by a method wherein particles ground to a suitable. state of fineness, i.e., preferably to domain size '-e.'g.,1 practicallv, /2 to 10 microns-are initially dispersedin'" a highly fluid medium such as water or other liquid free of solute and having a viscosity in centipoises not ex- Distributed in this medium, the particles are freely mobile, and they become oriented properly when the dispersion is subjected to a strong? magnetic field. Next, it has been found that, the disper-i si 0n medium may be evacuated, expelled, or withdrawn;v from the particles without disturbing directio nalization ofj tlie-particles to a significant degree. Various-methods for'acconiplishing this' result are subsequently disclosed;-,;

ceeding that of water.

to illustrate one practice of the method, the orientation Patented Dec. 20,19 0

may be conducted by introducing the dispersion into a cavity of a non-magnetic die equipped with a punch having a slight clearance with respect thereto whereby the pressure on the punch causes expulsion of the dispersion medium selectively while the particles remain in the die cavity. Peculiarly, there is very littlecarry-out or entrainment of solids with the suspension medium as it is expelled from the die, as contrasted with a large percentage of carry-out if a soluble binder is present in the sus pension liquid. Finally, the oriented particles in the compacted mass, which is now devoid or substantlally devoid of dispersion liquid, are immobilized into a machinable solid by establishing a solid immobilizing matrix in theinter-partiole spaces.

The immobilizing matrix may be a resinous, plastic, or elastomeric liquid as applied but is capable of hardening or setting to a solid state, or a metal having a low melting point applied to the compressed powder in a molten state and subsequently allowed to freeze therein. According to one method, the fiuid matrix is caused to enter the pores or voids between the particles and is set or hardened in the die from which the finished product is then discharged. According to an alternative method, the immobilizing matrix is established in situ. For this purpose, in a dispersion liquid having a viscosity not exceeding that of water, a co-suspension is formed of magnetic particles and particles of a normally solid, thermallysensitive resin which is insoluble in the dispersion liquid. Application of heat to the mass of particles after orientation of the magnetic phase and compression activates the thermally-sensitive resin particles to provide the desired coherence and physical stability without disturbing directional alignment of the magnetic phase. The matrix constitutes a continuous phase within which the particles are distributed and the finished product may be cut, drilled, tprned, or machined to desired shape or configuration.

By either technique of orienting the particles in a dis persion medium of low viscosity as disclosed, the high degree of mobility of the particles dispersed therein permits excellent magnetic orientation to be obtained. Because of the anisotropic nature of the particles, free rotatability thereof in the low viscosity medium allows them to move into alignment in a principal direction when an external magnetic field is applied, thereby producing in the finished product a preferred direction of magnetization parallel to the direction of the field.

' This'desirable orientation is not disturbed during the subsequent removal of the dispersion medium and the replacement thereof by the immobilizing matrix. For this reason, the method, depending upon the magnetic raw material chosen for use, provides a distinct improvement'over the results obtained by sintering a compressed mass of particles oriented within and cohered temporarily by a liquid binder. This technique also provides the distinct advantage of enabling the employment of very high pressures without substantial loss of solid material through carry-out, and a high degree of consolidation of the particles may therefore be obtained. This enables products having high energy to be produced without sintering. In addition, the establishment and retention of a matrix in the consolidated particles eliminates problems which would otherwise be encountered in stratification of the particles. Products displaying the unusual combination of good magnetic properties and free machinability may be produced from a variety of materials. Although the individual ceramic particles constituting the magnetic phase of the finished product possess their usual hardness, the application of a cutting tool to the finished product seversthe matrix and thereby readily permits the product to be shaped. Also, elimination of a final sintering step permits magnets of good properties to be pre pared'from lead ferritewhich heretofore was not possible because of the destructive elfect of the requiredsinter- In the drawings:

Figure 1 is a sectional view through a die adapted for the practice of the present invention showing the dispersion in the die cavity;

Figure 2 is a sectional view through a die having an enlarged impregnating cavity into which a binder may be introduced, showing the application of a magnetizing and aligning field to the die;

Figure 3 is a sectional view similar to Figure 2 but shows the punches moved downwardly to convey the magnetic briquet to the impregnating cavity into which an immobilizing matrix is being introduced;

Figure 4 is a sectional view similar to Figure 2 but shows the consolidated mass being raised from the impregnating cavity; and

Figure 5 is a sectional view similar to Figure 2 but shows the punches raised in position to permit the finished magnet to be removed from the die.

The following examples illustrate typical practice of the invention:

Example 1.-17.5 parts by weight of lead monoxide (1.5 mol PhD) is intimately mixed with 50 parts by weight of ferric oxide (6.0 mol Fe O This mixture is fired in a surrounding atmosphere of air, starting from, say, 700 C. and increasing the temperature gradually to 900 C. over a period of six hours in order to produce crystalline lead ferrite.

After quenching in air, the lead ferrite so produced is then ground in water for approximately 40 minutes in an attrition type mill after which it is removed, dried, and then heated for approximately 15 minutes at 500 C. to 750 C. A standard Szegvari attrition mill may be used with 7 stainless steel shot for the water grinding, during which the polycrystalline lead ferrite is reduced to domain size. The heat treatment after grinding is not es-. sential but is preferred because it increases the coercivity of the final product. This increase may be as much as depending on the magnitude'of heat treatment. Agglomerations of particles which may have formed during drying or heat treatment are eliminated by light milling of the ferrite powder.

A portion of the powdery lead ferrite so produced is admixed with acetone in the approximate ratio of 1 /2 cc. commercial acetone to one gram of lead ferrite to form a dispersion of the particles therein. This suspension is introduced into or formed within the cavity, 1 of a die 2 as shown" in Figure l of the accompanying drawing. The die cavity 2 is served by upper and lower movable punches Sand 4, and at the time of introduction of the suspension the lower punch 3 is in an intermediate position as shown. The body of metal containing the die cavity is non-magnetic, e.g., brass or bronze. but the punches 3 and 4 are of magnetic metal and serve as pole pieces of a magnetizing field coil which is conventional and therefore not shown.

After the suspension of acetone and lead ferrite is introduced into the cavity, with stirring if necessary to preserve the dispersion, top punch 4 is lowered to close the cavity, and an aligning field of approximately 2300 oersteds or higher is applied across the magnetic poles provided by the punches 3 and 4. In response to the magnetic field, the particles become aligned magnetically in a preferred direction parallel to the axis of the punches; the field strength increases as the punches approach one another. Punches 3 and 4 are constructed to fit cavity 1 with a slight degree of clearance, for example, .0005 to .001 inch, so that as pressure is applied, acetone escapes from the dispersion in cavity l while the particles remain in the cavity. By this means the acetone in which the particles are now aligned-with respect to one another is expelled, and the particles progressively become con- Iid I d- P l ma e Press r of pp t y 3 pe S u r nsh. armors is a pl ed. n as h sp act of 1.33 X10 H the aligning field increases from 2300 oersteds to approximately 15,000 oersteds.

At this time the pressure on the mass is relieved, and the compressedrmass, supported and retained by the upper and lower punches, is removed from the'immediate confines of the cavity 1 and immersed (approximately 30 minutes for example) in melted chlorinated naphtha lene (e.g. Halowax 1014) maintained as a bath at ;a temperature just above the melting point thereof (e.g. at 284 F.). During the immersion the immobilizing matrix enters the voids between the compressed particles and saturates the mass. The mass has great capacity to imbide the hydrophobic matrix-forming material. If desired, the compressed material may be heated to remove residual dispersion liquid from the compressed mass before the matrix is incorporated or established therein.

After this impregnation the entire assembly preferably is replaced in the die and, while in a field of 15,000 oersteds, is subjected to a coining operation under moderate heat and pressure (i.e., 500 to 25,000 p.s.i.), allowed to cool, and finally is removed. The purpose of the coining operation is to close and seal all cracks which might upon occasion tend to develop as high local stressesoccur during consolidation or upon release of pressure.

The permanent magnet produced by this methodhas residual induction Br of 2320 gauss, a coercive force He of 1540 oersteds, and a maximum energy product of 1.26 the BH rrlax, this, being the maximum value of the product of the induction B and the field H on the demagnetization curve. The combined apparent density of the product is 4.52 grams/cm. The permanent magnet produced by this method can be handled and worked freely without danger of breakage and may be cut readily with a knife or other edged tool.

From this example it will be seen that alignment of the particles and progressive consolidation occurs while the particles are freely mobile in a liquid of very low viscosity, the viscosity of acetone being .33- centipoises.

Example 2.-'Ihis example generally follows the pre-.

cedingexample except that the lead ferrite is initially ground for 1 /2 hours in water in the attrition mill (70 gram l oad), then heat treated for minutes at 850 C., and next subjected to a second water grinding operation in the attrition mill for a 15 minute period.- Upon admixture with acetone in the proportion and manner pre{- viously described and upon application of an initialaligning field of 2300 oersteds, the lead ferrite Pa ticles are material varies as to the nature of the ferrite, the manner in which it isprepared, the grinding period, the

nature of the matrix, and the method of incorporation thereof, and that, for a given set of conditions, a decrease in the pressure employed to effect consolidation lowers the maximum energy product andthe density.

As an illustration, a product was prepared according to, Example l but consolidation was effected at an ultimate pressure of 71,500 lbs." rather than the 36,000 lbs.

pensquare inch shown in Example 1,.and such product had a residual induction Br of 2400 gauss, a coercive force He of 1270 oersteds, and a maximum energy prod- 'Exumple 3. 1np1a of the waxy chlorinated naphthais as shown in Figure 3. Upon introduction of the matrix ceding examples, hardenable resinous, elastomeric or, plastic compositions, for example epoxy resin, castable phenol formaldehyde resin, polyestero, acrylic resin or the like, may be introduced into the voids of the consolidated powder mass as liquids and then set to solid state. .For this purpose in place of immersing the consolidatedmass in the matrix material while the mass is sustained between the punches by which it was compressed, the impregnation may be caused to occur in dies constructed as shown in Figures 2, 3, 4, and 5 of the accompanying drawing. In this instance the magnetic suspension is introduced into cavity 1 and compressed therein as previously described However, an impregnation cavity 5 is located at a lower level in the die block 2 in a position normally traversed by the lower punch 3 and this cavity is equipped with ports 6 and 7. After expulsion of the dispersion liquid and compression of the powder particles in die cavity 1, punches 3 and 4, with the compressed material confined between them, are lowered in unison until the compressed material resides within cavity 5. The briquette may be dried herein prior to impregnation. The immobilizing matrix material is now introduced under pressure through oneof the ports, e.g. 6, while a negative pressure may be maintained if necessary at the other of the ports 7. This:

material into the compressedmass of particles in this manner, punches 3 and 4 may be elevated to the position shown in Figure 4 wherein pressure may be applied to coin the mass as described in the preceding example,

; and if the immobilizing matrix is, a composition of the heat setting type, suitable'provision such as a high frefquency electrode surrounding die block 2 may be emproduct is cooled.

The punches 3 and 4 are now elevated to the position shown in Figure 5 to permit removal of the finished product.

Example 4.While a solution containing a binder dissolved therein suppresses particle mobility to such an extent that good alignment is retarded to a very substantial degree even though the percentage of dissolved binder isrelatively small, it has been found that free mobilityfl of the magnetically responsive particles is not impaired' by the presence of particles of a resin dispersed but not dissolved in a dispersed liquid having a viscosity not ex ceeding that of water. In this instance, upon a consolida-i tion of the magneto-crystalline particles the resinous'iparticles become consolidated therewith, and when the resin isof the heat-softenable or thermally-sensitive type, the

application of heat is eifective to develop a continuous of matrix which solidifies on cooling. In this way none the particles are disturbed as to alignment. This technique is illustrated as follows:

fLead ferrite prepared as described in Example l is i admixed with finely divided, alcohol insoluble polystyrene resin in the approximate ratio, taken on a solid. state basis, of 7 volumes of the lead ferrite powder to 3 volumes of polystyrene ground approximatelyto l00 mesh. The mixture is suspended in commercial ethyl alcohol, for example in the proportion of one gram of mixture to 1 /2 cc. alcohol, and a co-suspension is thereby produced of ferro-magnetic and matrix particles in the alcohol field. As in Example 1, this co-suspension may suitable.

of approximately 400 F. at which temperature the polystyrene softens and the remaining alcohol evaporates. The material is then subjected to a final consolidation presi has and. aw mat ix ma er a a s dins th are: t Sure of 1 59 s: Pe e r fi t i tmh 129rj net is cooled and removed. This product has a residual induction Br of 2400 gauss, a coercive force He of 1280 oersteds, and a maximum energy product of 1.El4 10 gauss oersteds. Density of the finished product is 4.33 grams/cmfi. This product, although very rigid, is readily machinable, has fair impact strength, and the edges of the sample do not crack or fall away under nominal shock.

Example 5.Lead ferrite prepared as in Example 1 is roughly mixed with polyethylene resin subdivided to -100 mesh, in the ratio of 7 volumes of ferrite to 3 volumes plastic, taken on a solid state basis. A co-suspension of the particles in the mixture is formed in acetone in which polyethylene is insoluble, a suitable ratio being one gram of mixture to 1 cc. acetone. After alignment and partial consolidation as described in the preceding example, the compressed mass is heated in the die to a temperature of 450 F. during which heating the plastic becomes adhesively soft and the residual acetone evaporates. After final consolidation at a pressure of 71,500 lbs. per square inch and cooling, the product displays a residual induction Br of 2200 gauss, a coercive force He of 1300 oersteds, a maximum energy product of 1.1X10 and a combined density of 4.16 grams/cm. This prod: uct has good impact strength and the edges hold up under severe shock.

Example 6.-Cosuspension of phenolic resin in water as a non-solvent therefor may be used in place of the combination shown in the preceding examples. In this case a thermosetting phenolic resin subdivided to l mesh is mixed in the ratio of 3 volumes thereof with 7 volumes of lead ferrite, and the co-suspension is formed by introducing one gram of the mixture into 1 /2 cc. of water. This mixture is then processed as described in Example 5 except that the temperature of the cavity 5 is raised to 250 F. or sufiiciently to soften the particles of phenolic resin and to evaporate any residual water. After subjecting the mixture to a final consolidation pressure of 71,500 lbs. per square inch, the product is finally cured by heating it to a temperature of approximately 325 F.

This product displays a residual induction Br of 2200 gauss, a coercive force He of 1250 oersteds, and a maximum energy product of 1.05 X The combined density of the mixed material is 4.1 grams/em Example 7.'-While lead ferrite has been disclosed as the selected ferro-magnetic material in the foregoing examples, barium and strontium ferrites, or mixtures thereof with each other or with lead ferrite, may be substituted.

To prepare strontium ferrite, the following procedure is satisfactory: 7.7 parts by weight of strontium carbonate (1 mol Sr C0 is intimately mixed with 50 parts by weight of ferric oxide (6 mol Fe O The mixture thus prepared is fired in an air atmosphere for approximately one hour and 45 minutes at a temperature of 1150 C. After quenching in air and to produce a more dense crystalline structure, the strontium ferrite so produced is pressed into pellets which are retired gradually from a starting temperature of 1100 C., to a maximum of approximately 1320" C. for a 30 minute period. After second quenching in air, the material is crushed and then ground with water for 25 minutes in the attrition mill. Upon drying of the ground material, it may be heat treated for minutes at 1000 C.

Example 8.Barium ferrite made as follows may be used in place of lead or strontium ferrite in any of the preceding examples: 10.3 parts by weight of barium carbonate (1 mol Ba C0 is intimately mixed with 50 parts by weight of ferric oxide (6 mol Fe o The mixture is fired in an air atmosphere for one hour and 45 minutes at a temperature of 1150 C. After quenching the material is preferably pressed into pellets and refired from a starting temperature of 1100 C. to a temperature of approximately 1320 C. over a 30' minute period. After quenching in air, the material is roughly crushed, then der moderate heat and pressure.

ground for 25 minutes with water in an attrition ype rnill, removed, and dried.

The strontium or barium ferrite made according to Examples 7 and 8 may be made into permanent magnets according to the methods shown in the preceding examples. In place of the alcohol, acetone, and water which have been disclosed as dispersing liquids in the foregoing examples, other liquids either organic or inorganic having a viscosity not exceeding or substantially exceeding that of water may be used successfully, such as benzene, xylene, tolene, or the like. Where the co-suspension procedure is to be employed, however, it is to be noted that a dispersion medium is chosen which does not act as a solvent for the particles or resin selected to form the matrix.

Example 9.Barium ferrite prepared as described in Example 8 is ground with water for 45 minutes in the attrition mill, then removed and dried. A portion of the ferrite produced in this manner is introduced into a nonmagnetic die along with acetone in the approximate radio of one gram of ferrite to each 1 /2 cc. of acetone. After positioning the punches, an initial aligning field of 2300 oersteds is applied, after which the powder is consolidated under a pressure of 61,000 lbs. per square inch. Following this, the compressed material is impregnated with chlorinated naphthalene according to the procedure described in Example 1. The product has a residual induction Br of 2280 gauss, a coercive force He of 1400 oersteds, a maximum energy product of 121x10, and an apparent density of 3.93 grams/cm.

Example 10.35 parts by weight of lead monoxide 1.5 mol PbO) is intimately mixed with parts of ferric oxide (60 mol Fe O The mixture thus prepared is fired in normal surrounding atmosphere gradually from 750 C. to a maximum temperature of 1050 C. over a period of five hours. After quenching in air, the ferrite is ground for a three hour period with water in the attrition mill, removed, dried, then heat treated for 15 minutes at 850 C. This is followed preferably by a second grinding operation in the attrition mill for a one hour period. The powder so produced is introduced into the die with the incorporation of acetone in the approximate ratio of one gram of ferrite to each 1 /2 cc. of acetone. Upon application of an initial aligning field of 2300 oersteds, the powder is then consolidated under a pressure of 50,000 p.s.i. The briquette is then impregnated by immersion in a low viscosity epoxy resin and is subjected finally to a coining and curing operation un- This product has a residual induction of 2480 gauss, a coercive force of 2160 oersteds, and a maximum energy product of 15x10. The combined apparent density of the mixed material is 4.14 grams/cmfi.

Those skilled in the art readily will understand that a wide variety of thermo-plastic materials may be used to form the matrix, as well as plasticols, waxes, and the like. The method of incorporation of the matrix-forming material with the consolidated and aligned particles, 'of course, will depend upon the natureof the selected matrix-forming material. Where it is a normally solid thermo-setting resin such as a phenolic or urea formaldehyde, or is a heat-softenable material such as cellulose acetate, the formation of a co-suspension of the particles of resin with theparticles of magnetic powder in a dis persion liquid provides an excellent means of establishing the matrix without interfering with orientation of the magnetic particles. In such instances, where heating is required to set the resin, the same maybe accomplished in the die such as by means of a high frequency electrode or other suitable heating means. If the matrix-forming material is a hardenable liquid or is in a molten condition, it may be introduced by impregnation or injection,

for example in accordance with the injection molding" technique. Byvir'tue of the fact that orientation of the particles is conducted by subjecting them to a directionalized magnetic field, the particles become magnetized; and in view of the fact that they are not subsequently subjected to temperatures adversely affecting the magnetization which they have acquired during orientation, a final magnetizing step as is conventional with other materials is not requisite, although such a step may be employed if desired as an extra precaution to insure uniformity of product.

Having described my invention, I claim:

1. A method of making a permanent magnet which method comprises, subdividing a ceramic composition selected from the class consisting of barium, strontium, and lead ferrite into small particles, dispersing the particles in a liquid medium having a viscosity not exceeding the viscosity of water, subjecting the dispersion to a magnetic field thereby aligning the particles in a principal direction, consolidating the aligned particles while removing therefrom the liquid in which they have been dispersed during alignment, introducing a normally solid and machinable liquid matrix-forming material into the voids between the aligned particles and solidifying said matrix thereby producing a machinable, anisotropic permanent magnet.

2. A method of making a permanent magnet material which method comprises, subdividing a ceramic composition selected from the class consisting of barium, strontium, and lead ferrite into small particles, dispersing the particles in water, subjecting the dispersion to a magnetic field thereby aligning the particles in a principal direction, consolidating the aligned particles while removing therefrom the liquid in which they have been dispersed during alignment, introducing a normally solid and machinable liquid matrix-forming material into the voids between the aligned particles and solidifying sa-id matrix, thereby producing an anisotropic permanent magnet material which is machinable by edge cutting tools.

3. The method of making a permanent magnet material which comprises, subdividing a magneto-ceramic composition of the class consisting of barium, strontium, and lead ferrite into substantially domain sized particles, forming a co-suspension of said particles and particles of a non-magnetic, heat softenable, matrix-forming material in a dispersion liquid having a viscosity less than water in which the particles of said matrix-forming material are insoluble, subjecting said co-suspension to a magnetic field to align the ferrite particles in a principal direction, removing said dispersion liquid and consolidating all of said particles under pressure to produce a compact mass and under heat sufficient to cause flow of the matrixforming material into the voids and openings between the ferrite particles.

4. The method of claim 3 in which the dispersion liquid is an organic solvent and the matrix-forming particles are insoluble therein.

5. The method of making a permanent magnet material which comprises, subdividing a magneto-ceramic composition of the class consisting of barium, strontium, and lead ferrite into substantially domain size particles, dispersing the particles in a liquid medium having a viscosity not greater than that of water in which liquid medium are suspended insoluble particles of a matrix material, orienting the ferrite particles while dispersed therein in a preferential direction of magnetization, removing the liquid medium from the particles and immobilizing the oriented ferrite particles in the matrix material.

6. The method of making a permanent magnet material which comprises, subdividing a magneto-ceramic composition of the class consisting of barium, strontium, and lead ferrite into substantially domain size particles, dispersing the particles in water, orienting the particles while dispersed therein in a preferential direction of magnetization, removing the water from the particles, immobilizing the oriented particles in a matrix of normally solid material, and then solidifying said matrix.

7. The method of making a permanent magnet material which comprises, subdividing a magneto-ceramic composition of the class consisting of barium, strontium, and lead ferrite into substantially domain size particles, dispersing the particles in an organic liquid having a viscosity not greater than that of water, subjecting the particles while dispersed in said organic liquid to a magnetic field whereby the preferred directions of magnetization of the particles are aligned, removing the liquid from the panticles, immobilizing the aligned particles in a matrix of normally solid material, and then solidifying said matrix.

8. The method of making a permanent magnet material which comprises, subdividing a magneto-ceramic composition of the class consisting of barium, strontium, and lead ferrite into substantially domain size particles, dispersing the particles in a liquid medium having a viscosity not greater than that of water, subjecting the particles while dispersed in said liquid medium to a magnetic field whereby the preferred directions of magnetization of said particles are substantially aligned, removing the liquid medium from the particles, immobilizing the oriented particles by introducing a solidifiable plastic material into the interparticle voids and openings and solidifying said plastic material.

9. The method of making an edge cuttable permanent magnet material which comprises, subdividing a magnetically anisotropic permanent magnet material into substantially domain size particles, dispersing the particles in a liquid medium having a viscosity not greater than that of water, subjecting the dispersion to a magnetic field so that the preferred magnetic directions of the particles therein are aligned substantially parallel to each other, consolidating the aligned particles while removing therefrom the liquid medium in which the particles were dispersed, and immobilizing the aligned particles in an edge cuttable, non-magnetic matrix.

10. The method of making an edge cuttable permanent magnet material which comprises, subdividing a magnetically anisotropic permanent magnet material into substantially domain size particles, forming a co-suspension of said particles and particles of a flowable, hardenable, nommagnetic, edge cuttable matrix material in a liquid medium having a viscosity not greater than that of water, said particles of matrix material being insoluble in said liquid medium, subjecting the co-suspension to a magnetic field so that the preferred magnetic directions of said magnetic particles are aligned substantially parallel to each other, consolidating the aligned magnetic particles and the particles of matrix material while removing therefrom the liquid medium in which the particles were suspended, and immobilizing the aligned magnetic particles in the matrix material.

References Cited in the file of this patent UNITED STATES PATENTS 1,721,379 Ehlers et a1 July 16, 1929 1,946,964 Cobb Feb. 13, 1934 2,064,773 Vogt Dec. 15, 1936 2,238,893 Fischer Apr. 22, 1941 2,503,947 Haskew Apr. 11, 1950 2,532,876 Asche et al. Dec. 5, 1950 2,601,212 Polydorofi June 17, 1952 2,677,663 Jonker et al. May 4, 1954 2,744,040 Altmann May 1, 1956 2,744,873 Piekarski May 8, 1956 2,762,778 Gorter et al. Sept. 11, 1956 2,827,437 Rathernau Mar. 18, 1958 2,849,312 Peterman Aug. 26, 1958

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