CA1277159C - Isotropic permanent magnets and process for producing same - Google Patents

Abstract

ABSTRACT
ISOTROPIC PERMANENT MAGNETS AND PROCESS
FOR PRODUCING SAME
Isotropic permanent magnet formed of a sintered body having a mean crystal grain size of 1 - 160 microns and a major phase of tetragonal system comprising, in atomic percent, 10 - 25 % of R wherein R represents at least one of rare-earth elements including Y, 3 - 23 % of B and the balance being Fe. As additional elements M, Al, Ti, V, Cr, Mn, Zr, Hf, Nb, Ta, Mo, Ge, Sb, Sn, Bi, Ni or W may be incorporated.
The magnets can be produced through a powder metallurgical process resulting in high magnetic properties, e.g., up to 7 MGOe or higher energy product.

Description

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SPECIFICATION

TITLE OF THE INVENTION
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ISOTROPIC PER~NENT MAGNETS ~JD PROCESS
FOR PRODUCING SAME

FIELD OF THF INVENTION
The present invention relates generally to isotropic permanent magnets and, more particularly, to novel magnets based on FeER alloys and expressed in terms of FeER and FeE3P~M.
In the present disclosure, t~e term "isotropy" or "isotropic" is used with respect to magnetic properties. In the present invention, R is used as a symbol to indicate rare-earth elements includirlcJ yttrium Y, M is used as a symbol to denote additional elements such as Al, Ti, V, Cr, Mn, Zr, El~, .' ' . , . , - .
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t~b, Ta, Mo, Ge, Sbt Sn, Bir ~i and ~7, and ~ is used as a sym~ol to refer to elements such as copper Cu, phosphorus P, carbon C, sulfur S, calcium Ca, magnesium ~Ig, oxygen O and silicon Si.

BACKGROU~lD OF TtlE I~VEMTIOI~
Permanent rnagnets are one functional material which is practically indispensable for electronic equipment. The permanent magnets currently in use mainly include alnico magnets, ferrite magnets, r2re earth-cobalt (RCo) magnets and more. with remarkable advances in semiconductor devices in recent years, it is increasingly required to miniaturize and upgrade the parts corresponding to hands and reet or mouths (voice output devices) thereof. Tne permanent magnets used trlerefor are required to possess high properties correspondingly.
Although, among permanent rnagnets, the isotropic permanent masnets are inrerior to the anisotropic magnets in certain points in view of performance, the isotropic magnets ~ind good use due to such magnetic properties that no limitation is imposed upon the shape and the direction of rnagnetization. ~lowever, t~lere is much to be desired in performance. The anisotropic magnets rather than the isotropic magnets are generally put to practical use due to their hiyh performance. Although the isotropic magnets are substantially formed of the same material as the anisotropic magnets, for inst2nce, alnico ~agnets, ferrite : ,' :' , ' ' ~277~

magnets, l~nl~l magnets and F`eCrCo magnets show a maximum energy proauct (~I)max of barely 2 ~;GOe. SmCo magnets broken aown into ~Co magnets show a relatively high value on the order of 4-5 r~oe, wllich is nonetheless only 1/4 - 1/6 times those of tne anisotropic magnets. In aaaition, the SmCo magnets still offer some problems in connection with practicality, since they are very expensive because of the ract that samarium Sm hich is rzre is needed, and that it is required to use a large amount, i.e., 50-60 weight % of cobalt Co, the supply of which is uncertain.
It has been desired in the art to use rela~vely ahw~ant lightrare-~ ~ elernents such as, for example, Ce, Nd, Pr an~ the like in ; place of Sm belonging to heavy rare earth ana substitute Co with Fe. However, it is well-l;nown that light rare earth elements and Fe do not form intermetallic canpounds sui ~ le for magnets, even when they are mutually melted in a homogeneous state, and crystallized by cooling. Furthermore, an attempt made to improve the magnetic force of such light rare earth-Fe alloys through powder metallurgical manners ~as also unsuccessful (see JP Patent Xol;ai (Laià-Open) Publication No. 57 2)-21093~, pp. 6).
On the other hand, it is l;nown that amorpllous alloys based on (Fe, Ni, Co)-R can be obtained by rnelt-qllenching. In particular, it ~as been proposed (in the a~oresaid Publication No. 57-210934) to prepare amorphous ribbons from binary alloys based on Fe~ ~as R use is ~ade o~ Ce, Pr, Na, Sm, ~u, etc.~, especially F~ld and ma~netizing the ribbons, w~ereby magllets ~`~

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are o~tained. This process yielcls magnets having (BH)max of 4-5 I;GOe. ~-]owever, since the resulting ribbons have a thickness ransing from several microns to a few tens of microns, they should be laminated or compacteci after pulverization in order to obtain magnets of practical bulk. ~ith any existing methods, a lowering of density and a further lowering of magnetic properties woul~ t~ke place. Aiter all, it is not feasible to introduce improvements in maqnetic prc~erties.

SUI~ .P~Y OF THE INVE~TIOIl It i5 a principal object of the present invention to provide novel permanent magnets superseding the conventional isotropic permanent magnet materials.
~ lore particularly, the present invention aims at providing isotropic permanent magnets (ancl materials) having magnetic properties equivalent to, or greater than, those of the coventional products, in which rela-tively abundant materials, especially Fe, and relatively abundant rare-earth elements are mainly used, and in which Sm and the like having problems in availability are not necessarily used as R.
~ urthermore, the present invention aims at providing isotropic permanent magnets having improved magnetic properties such as improve~ coercive force.
In addition, the present invention aims at providing isotropic permanent ma~nets which are ine~:~ensive, but are practical of su~icient value.
The present invention also aims at providing a process .,,~

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for the production of these magnets.
~ ccording to lst-3rd aspects of the present invention, there are proviaed magnetically isotropic sintered permanent magnets based on FeBR type compositions. ~lore specifically, accordiny to the first aspect, there is provided an isotropic sintere~ p~rmanent magnet based on FeB~; accordlng to the second asE~ect, tnere is provided an Fe~R base rnagnet, the mean crystal ~rain size of which is 1-160 microns after sinteriny;
and according to the third aspect, there is provided a process for the production of the Fe~P~ t~ase, isotropic sintered permanent magnets as referred to in the fIrst and second aspects.
The 4~h-6th aspects of the present invention relate to FeE~l type COMpOSitiOnS ~ore specifically, according to the fourth aspect, there is provided an isotropic permanent magnet based on FeBRrl; according to the fifth aspect, there is provided a FeBRM base magnet, the mean crystal grain size of which is 1-100 r,licrons after sintering; and according to the sixth aspect, there is provlueq a process for the prouuction of tt~e magnets as referred to in the fcurth and fifth aspects.
The seventh aspect of ttle present invention is concerned with an allowable level of impurities, which is applicable to the FeE~ and FeBRt~ systems alike, and offers adv~ntages in view of the practical proauct~ and the process of production thereof as well as commerical productivity.
In the present disclosure, "%" means "atomic g" unless otherwise specified.
l'hus, the isotropic permanent magnets according to the , ' ~277~5~3 first aspect of the present lnvention are characterized in t~at they have a composition ~hereinafter referred to "the Fe~R composition or system") comprising, in atomic percent, 10-25 % of R, 3-23 % of boron B and the balance being iron Fe and inevitable impurities, are isotropic, and are obtained as sintered bodies by powder metallurgy~
The isotropic permanent magnets according to the second aspect of the present invention are characterized in that they have the aforesaid FeBP~ composition, and the sintered bodies have a mean crystal grain size of 1-160 microns after sintering.
The process of prouuction according to the third aspect or the present invention will be described later together with that according to the sixth aspect of the present invention.
- The present inventors already invented FeBR base, anisotropic permanent magnets in which Sm and Co were not necessarily used. As a result of intensive studies of isotropic permanent magnets, it has furtner been found that permanent magrlets s~.o~lng c~ooci isotropy can be o~tained from the FeBR systems ~ith the application of sintering. Gased on such findingc, the l~resent invention has been accomplished.
The FeB~ basod, isotropic permanent macJnets o~tained according to the present invention have properties equivalent to, or greater than, those of the SmCo based, isotropic magnets, ! and are inexpensive and of extremely high practical value, since expensive Sm is not necessarily used and there i`s no need of using Co.
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In ttle present invention, the term "i50~0py" iS used to indicate one of the properties of the permanent magnets and means that they are substantially isotropic, i.e., in a sense that no magnetic field is impressed during compacting or forming, and also includes isotrop~ that may a~pear by compacting or forming.
The isotropic sintered perm~nent magnets according to the fourth aspect of the present invention have a composition based on Fe~RM (hereinafter referred to nthe FeBE~I composition or systemn), wllich comprises, in atomic percent, 10-25 % of R
(provided that R is at least one of rare-earth elements including.Y), 3-23 % of boron B, no more than given percents (as specified below) of one or two or more of the following : additional elements M (exclusive of M = O %, provided that, ~ when two or more additional elements M are added, the combined : amount of M is no more than the maximum value among the values, specified below, of said elements M actually adoed~, and the balance being Fe and inevitable impurities entrained from the process of production:
9.5 ~ ~l, 4.7 ~ Ti, 10.5 % V, 8.5 ~ Cr, 8.0 ~ Mn, 5.5 % Zr, 5.5 % ~If, 12.5 % Nb, ; 10.5 '~ Ta, 8.7 ~ Mo, 6.0 % Ge, 2.5 ~ Sb, 3.5 ~ Sn, 5.0 % Bi, 4.7 % Ni, 8.8 % W.
~ ccordiny to the fifth aspect of the present invention, there is provided the permanent magnet of the fourth aspect in which the sintered body has a mean crystal grain size ranging from about 1 micron to about 100 microns.

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The isotropic sintered permanent magnets according to t~le seventh aspect of the present invention cvmprises the FeBR
and FeBRM compositions in which one or more of A are further contained in given percents. A stands for no more than 3.3 %
copper Cu, no more than 2.5 ~ sulfur S, no more than 4.0 ~
carbon C, no more than 3.3 ~ phophorus P, each no more than 4.0 % Ca and llg, no more thaD 2.0 ~ O and no more than 5.0 Si. It is noted that the combined amount of A is no more than the maximum value among the values specified above of said elements A actually contained, and, when M and A are contained, the sum of M plus A is no more than the maximum value among the values specified above of said elements M and A actually adde~ and containedO
The permanent magnets are obtained as magnetically isotropic sintered bodies, a process for the preparation of which is herein disclosed and characterized in that the respective alloy po~ders of the FeBR an~ FeB~I compositions are compacted, followed by sintering ~the third and sixth aspects)~ It is noted that the alloy powders are novel and crystalline rather than amorphous~ For instance, the starting alloys are prepared by melting, and cooled. The thus cooled alloys are pulverized, compacted under pressure and sintered resulting in isotropic permanent magnets. Cooling of the molteil alloys may usually be done by casting and other cooling manners.

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- 8a -In one specific embodiment of the invention there is provided a powder me~allurgically sintered, isotropic permanent magnet having a mean crystal grain size of 1-80 microns and consisting essentially of, by atomic percent, 12-20 percent R wherein R is at least one element selected rom the group consisting of Nd, Pr, La, Ce, Tb, Dy, Ho, Er, Eu, Sm, Gd, Pm, Tm~ Yb, Lu and Y and wherein at least 50% of R consists of Nd and/or Pr, 5-18 percent B, from zero tO) percent of M to an amount of M not exceeding the atomic percentages specified below, M being selected from the group given below, wherein the sum of M does not exceed the maximum value of any one of the values specified below for M actually added, M being:
7.8% Al, 3.8~ Ti, 7.8% V, 6.9% Cr, 6.9% Mn, 4.8~ Zr, 4.5% Hf, 10.0~ Nb, 8.8% Ta, 7.6% Mo, 5.0~ Ge, 2.0~ Sb, 2.7~ Sn, 4.2~ Bi, 3.8~ Ni, and 7.9~ W, and at least 62 percent Fe, in which at least 50 vol. % of the entire magnet is occupied by an Fe-B-R type ferro-: 20 magnetic compound having a substantially tetragonal crystal structure, said magnet having a maximum energy product of at least 5 MGOe and an intrinsic coercivity oE at least 1 kOe.
Preferred embodiments of the present invention will now be explained in further detail with re~erence to ~he .

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1~77~9 g accompanylng drawings illustrating examples. It is understood t~lat the present invention is not limited to the embodiments illustrated in the drawings.

B~IEF DE5CP~IPTION OF T~IE DRAWINGS
Fig. 1 is a graph showincJ the relationship between the amount of R ~Nd) and coercive force iHc as well as residual magnetic flux density Br;
j Fig. 2 is a graph showiny the relationship between the ! amount of B and iHC as well as Br, Fig~ 3 is a graph showing the relationship between the the mean crystal grain size distribution and the coercive force in one example o~ the present invention;
Fig. 4 is a graph showing the relationship between the amo~nt o~ some of the element~ A and Br in the FeBP~ system (Fe-8B-15Nd-xA~;
Figs. 5 and 6 are graphs showing the amounts of R and B, and Br and iHc of the FeBRM systems (Fe-8B-xNd-lMo, Fe-xB 15Na-lMo), respectively;
Figs. 7 and 8 are grAphs showing the relationship between the amoùnt of M and Br in the FeERxM system ~Fe-8B-15Nd-xM); and Fig. 9 is a graph showing the relationship between the the mean crystal grain size distribution o sintered bodies and iHc in ~he FeBR~I systems ~Fe-8E-15Nd-2Al and Fe-8B-15Nd-lMo).

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GENER~ L I~D FIRSq' ASPECT
The FeER, FeB~, FeERtl and Fe~N~ systems of the present invention are all ba-~ed on the PeBR system, and are similarly determined in respect of the ranges of B and R.
To meet a coercive force iHc of no less than 1 kOe, the amount of B should be no less than 3 atomic ~ ~hereinaEter ~"
stands for the atomic percent in the alloys) in tkle present invention. An increase in the amount of B increases iHc but decreases Br (see Figs. 2 and 6). Hence, the amount of B
should be no more than 23 % to obtain Br of at least 3 kG
and to achieve (BHjmax of no less than 2 MGOe.
Figs. 1 and 5 (wherein M denotes llo) are illustrative of the relationship between the amount of R and iHc as well as Br in the FeBR and FeBRM systems. As ~he amount of R
increases, iHc increases, but Br increases then decreases depicting a peak. Hence, the amount of R should be no less than 10 ~ to obtain (BH)max of no less than 2 I1.GOe, and should be no more than 25 % for similar reasons and due to the f~ct that , R is expensive, and so likely to burn that difficulties are involved in technical handling and production.
Preferable with respect to ~e, B and R are the FeBR
compositions in which R is 12-20 % ~/ith the main component being light rare earth such as t~d or Pr (the light rare earth amounting to 50 % or higher of the overall R)t B is 5-18 ~ and the balance is Fe, and the Fe~l compositions wherein the aforesaid ranges }~old for Fe, B and ~, and 1l is urther within a rarlge providing at least 4 ~;G Br, since it is then possible . ...
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to achieve high magnetic properties represented by (EH)ma~ of no less than 4 t~Oe.
Most preferable with respect to Fe, B and R are the FeBR compositions in which R is 12-16 ~ with the main component beiny light rare earth such as Nd or Pr, B is 6~18 %
and the balance being ~e, and the F~eBR~I compositions wherein the aforesaid ranges hold for Fe, B and R, and M is within a range providing at least 6 kG Br, since it is then possible to achieve high properties represented by (~H)max of no less than 7 MGOe, which has never been obtained in the conventional isotropic permanent magnets.
The present invention is very useful, since the raw materials are inex~ensive owing to the fact that abundant rare earth elements which might otherwise find no wide use elsewhere can be used as R, and that Sm is not necessarily used, and may not be used as the main ingredient.
Besides Y, R used in the permanent magnets of the present invention includes light- and heavy-rare earth, and at least one thereof may be used. That is, use may be made of Nd, Pr, lanthanum La, cerium Ce, terbium Te, dysprosium Dy, holmium ~lo, erbium Er, europium Eu, samarium sm, gadolinium Gd, promethium Pm, thulium Tm, ytterbium Yb, lutetium Lu, Y
and the like. It suffices to use light rare earth as R, and particular preference is given to Nd and Pr, e.g., no less than 50 % of R or mainly of R. Usually, it suffices to use one element as ~, but, practically, use may be made of mi~tures of two or more elements such as mischmetal, ~ydimium, ,., .~

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may be used in the form of mixtures with light rare earth such as Nd and Pr. R may not be pure liyht rare- earth elements, and contain inevitable impurities entrained f rom the process of production (other rare-earth elements, Ca, Mg, Fe, Ti, C, O, etc. ), as lony as such R is industrially available.
The startinc; B rnay be pure boron or alloys of B wit other constitutional elernents such as ferroboron, and may contain as impurities Alr C~ silicon Si and more. The same 10 holds for all the aspects of the present invention.

THIP~D ASPECT (Producing Process) The FeBP~ base permanent magnets disclosed in the prior application are obtained as magnetically anisotropic sintered bodie~, and the permanent magnets of the present invention are obtained as similar sintered bodies, except that they are isotropic. In other words, the isotropic permanent magnets of the present invention are obtained by preparing alloys, e.g., by rnelting and cooling and pulverizing, compacting and sintering the alloy com~)acts.

Melting may be carried out in vacuo or in an inert gas atrnosphere, and cooling may be e~ected by, e.g., castiny.
For castiny, a mold formed of copper or other metals may be used. In the present invention, it is desired that a ~,later-cooled type mold is used with the application of a rapid cooling rate to prevent segregation of the ingredients of ingot alloys. ~fter sufficeint cooling, the alloys are .
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coarsely ground in a stamp mill or like means an~, then, finely pulverized in an attritor, ball mill or li~e means to no more than about 400 microns, preferably 1-100 microns.
In addition to the aforesaid pulverization manner, mechanical pulverization means such as spraying and physicochemical pulverization means such as re~ucing or electrolytic rneans may be relied upon for the pulverizatiorl of the FeBR bac:e alloysv The alloys of the present invention may be obtained by a so-called direct re~uction process in which 10 the oxides of rare earth are directly reduced in the presence of other constitutional elements (e.g., Fe and B or an alloy thereof) with the use of a reducing agent such as Ca, l~g or the likeO
The finely pulverized alloys are formulated into a ; given composltion. In this case, the FeBR base or mother alloys may partly be added with constitutional elements or alloys thereof for the purpose of adjusting the composition.
The alloy powders fonnulated to the given composition are compacted under pressure in the conventional manner, and the 20 resultant compact is sintered at a temperature approximately of 900-1200 C~ preferably 1050-1150 C for a given period of time. ~t is possible to obtain the isotropic sintered magnet bodies having high maynetic properties by selecting the sintering conditiorls ~especially temperature and time) in such a manner that the mean crystal ~rain size oE the sintered bodies comes within the predetermined range after sintering.
For lnstance, sintered bodies having a preEerable mean crystal .

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grain size can be obtained by compacting the C:tarting alloy powders having a particle size of no more than 100 microns, followed by sintering at 1050-1150 DC Eor 30 minutes to 8 hours.
It is noted that sintering is carried out preferably in vacuo or in an inert gas atmosphere which may be vacuo or reduced pressure, e.g., 10 2 Torr or le5S or inert or reducing gas with a purity of 99.9 % or higher at 1 - 760 Torr. Duriny compactiny, use may be made of bonding agents such as camphor, paraffin, resins, ammonium chloride or the like and lubricants or compacting aids such as zinc stearate, calcium stearate, paraffin, resins or the like.

EXA~IPLES ~First-Third Aspects) The first-third aspects of the present invention will now be elucidated with reference to examples, which are given for the purpose of illustration alone and are not intended to impose any limitation upon the present invention.
Samples of 77Fe-8B-15~Jd were prepared by the following steps. In what follows, the unit of purity ls weight %~
(1) Referriny to the startiny materials, electrolytic iron - of 99.9 ~ purity ~1AS used as Fe; a ~erroboron alloy containing 19.4 % of B ~ith the balance being Fe and impurities of ~1, Si and C AS B; and rare earth of 99.7 % purity or higher as R
limpurities were mainly other rare-earth metals). These materials were fomulated into a given atomic ratio, melted and cast in a water-cooled copper molcj.

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i9 ~2) The cooled alloy was coarsely st~mp-milled to 35-mesh through and, then, finely pulverized for 3 hours in a ball mill to 3-10 r.licrons.
(3) The resultant powders were compacted under a pressure of 1.5 t/cm2.
(4) Sintering was carried out at 1000-1200 C for 1 hour in argon .in such a manner that the mean crystal grain size of the sintered body came within a range of 5-30 microns, followed by allowing the body to cool which resulted in the samples.
The permanent magnet samples shown in Table 1 prepared by the foregoing steps were measured for the magnetic properties iHc, Br and (BH)max thereof. Table 1 shows the .r magnetic properties of tne individual samples at room ~ ~ .
temperature.
Within the given ranges of the respective ingredients, il~c of no less than 1 kOe and Br of no less than 3 kG were obtained. (BH)max of no less than 2.0 I~GOe was also obtained.
Thus, high magnetic properties are obtained.
It is found that the combination of two or more rare-earth elements is also useful as R. To make a close examination of the relationship between the amounts of R and B
and the magnetic properties, a number of samples were prepared by the same steps on the basis of Fe-eB-xt~d systems wherein x = 0 - 35 % and Fe-xB-15Nd systems wherein x - 0 - 30 %.
Tables 1 and 2 show the iHc and Br measurements of the samples.

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Table 1 _ __ , magnetic properties ~:
___ No. compositions (at %) iHc(kOe) Br(kG) ¦MGOe) i _ Cl 85Fe-15Nd O O O
C2 55Fe-30B-15Nd 10.8 1.8 0.7 C3 76Fe-19B-5Pr O O O
C4 53Fe 17B-30Nd 13.5 2.2 1.0 l 1 82Fe-3B-15Nd 1~7 5.2 2.0 : 2 80Fe-5B-15Nd 3.4 5.3 4.5 . 3 77Fe-8B-15Nd 8.5 6.4 8.7 . 4 68Fe-17B-15Nd 7.2 4.8 4.6 7OFe-17B-13Nd 5.3 4.9 4.8 6 65Fe-12B-22Pr 11.0 3.4 2.3 7 63Fe-17B-lONd-5Pr 7.2 4.7 4.1 . 8 75Fe-lOB-8Nd-7Pr 7.4 6.2 7.8 9 68Fe-19B-8Nd-5Pr-2La 6.6 3.6 2.6 75Fe-lOB-18Ho 6.0 3.2 2.1 11 7OFe-lOB lOEr-5Pr 4.7 3.1 2.2 75Fe-lOB-lONd-4Dy-lSm 3.8 ~ 3~6 , : ,,, :
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Like the ferrite or RCo magnets, the permanent magnets of the FeBR base sintered bodies are the single domain, fine particle type magnets, which give rise to unpreferable magnet properties without being subjected- to once pulverization followed by compacting under pressure and sintering~
With the single domain, fine particle type magnets, no magnetic walls are present within the fine particles, so that the inversion of magnetization is effected only by rotation,-wilich contributes to further increases in coercive force.
To this end, the relationship was investigated between the crystal grain size and th~ magnetic properties~
par~icularly i~c, of the permanent masnets of the FeBR base sintered bodies according to the present invention, based on the Fe-8B-15~d system. The results are given in Fig. 3.
The mean crystal grain size should be within a range of 1-160 microns to achieve iHc of no less than 1 kOe, and within a range of 1 110 microns to achieve iHc of no less than 2 kOe.
A range of 1-80 microns is preferable, and a range of 3-10 ~icrons is most preferable.

CP~YSTAL STRUCTURE
The present inventors have already disclosed in detail the crystal structure of the magnetic materials and sintered magnets based on the FeBR base alloys in prior Canadian Patent Application Serial No. 431,730 (filed on July 4, 1983), subject to the preponderence of the .
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~ 7 disclosure recited in this application. The same is also applied to the FeBRM system.
Referring generally to the crystal structure, it is believed that the magnetic material and permanent magnets based on the Fe-B-R alloy according to the present invention can satisfactorily exhibit their own magnetic properties due to the fact that the major phase is formed by the substantially tetragonal crystals oE the Fe-B-R type. Tle Fe-~-R type alloy is characterized by its hiyh Curie point and lO it has further been experimentally ascertained that the presence of the substantially tetragonal crystals of the - Fe-B-R type contributes to the e~hibition of magnetic ., .
properties. The contribution of the Fe-B-R base tetragonal system alloy to the magnetic properties is unknown in the art, and serves to provide a vital guiding principle for the production of magnetic materials and permanent magnets having high magnetic properties as aimed at in the present invention.
The tetragonal system of the Fe-B-R type alloys according to the present invention has lattice constarlts of Qo : about 8.8 A and Co : about 12.2 A. It is useEul where this tetragonal system compounds constitute the major phase of the Fe-B-R type magnets, i.e., it should occupy 50 vol ~ or more of the crystal structure in order to yield practical and good magnetic properties.
Besides the suitable mean crystal grain size of the Fe-B-R base alloys as discussed hereinabove the presence of a Rare earth lR) rich phase (i.e., including about 50 at % of R) , `' " , ' , , ..

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serves to yield of good magnetic properties, e.g., the presence of 1 vol % or more of such R-rich phase is very effective.

The Fe-B-R tetragonal system compounds are present in a wide compositional range, and may be present in a stable state also upon addition of certain elements other than R, Fe and B.
The magnetically effective tetragonal system may be "substantially tetragonal~ which term comprises ones that have a slightly deflected angle between a, b and c axes, e.g., within about 1 degree, or ones that have ~o slightly different from bo, e.g. within about 1 %.
The same is applied to the FeBRM system.
The aforesaid fundamental tetragonal system compounds are stable and provide good permanent magnets, even when they contain up to 1 % of H, Li, Na, K, Be, Sr, Ba, Ag, Zn, N, F, Se, Te, Pb, or the like.
As mentioned above, contribution of the Fe-B-R type tetragonal system compounds to the magnetic properties have been entirely unknown in the art. It is thus a new fact that high magnetic properties suitable for permanent magnets are obtained by ~orming the major phases with these new compounds.

In the field of R-Fe alloys, it has been reported to prepare ribbon magnets by melt-quenching. However, the invented magnets are different from the ribbon magnets in the ~ollowing several points. That is to say, the ribbon magnets can e~hibit permanent magnetic properties in a transition stage from the amorphous or metastable crystal phase to the stable crystal '~

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~7~i9 state. Reportedly, the ribbon magnets can exhibit highcoercive force only if the amorphous state still remains, or otherwise metastable ~e3B and R6Fe23 are present as the major phases. The invented magnets have no signs of any alloy phase remaining in the amorphous state, and the major phases thereof are not Fe3B and R6Fe23.
When the magnets of the present invention are prepared, use may be made of granulated powders (on the order of several tens-several hundreds microns) obtained by adding binders and lubricants to the alloy powders. The binders and lubricants are not usually employed for the forming of anisotropic magnets, since they disturb orientation. However, they can be incorporated into the magnets of the present invention, since the inventive magnets are isotropic. Furthermore, the incorporation of such agents would possibly result in improvements in the efficiency of compacting and the strength of the compacted bodies.
In preferred embodiments, the isotropic permanent magnets obtained according to the present invention have the magnetic properties higher than those of all the existing isotropic permanent magnets and, moreover, do not rely upon expensive ingredients such as Sm and Co. The present invention is also highly advantageous in the it is possible to manufacture magnet products of practically sufficient bulk that is by no means achieved in the proposed amorphous rlbbon process.
As stated in detail in the foregoing, the FeBR base ...,~

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, - ' "'' isotropic permanent magnets according to the first-third aspects of the present invention give high magnetic properties, makirlg use of inexpensive P~ materials such as light rare earth (especially ~Id, Pr, etc.), particularly various miY.tures of light- and heavy-rare earth.

~OURTH ~SPECT
~ ccording to the fourth aspect of the present invention, aciditional elements M are aclcled to the FeBR base alloys as ciisclosea in the first-third aspects to contemplate 10 improviny in principle the coercive force iHc thereof.
Namely, the incorporation of M yives rise to a steep increase in iHc upon increase in the amount of B or R. Generally, as B
or R increases Br rises and decreases after depicting a maximum value, wherein M brings about increase of iE~c just in a maximum range of Br. As M, use may be made of one or more of Al, Ti, V, Cr, Mn, Zr, ~f, Nb, Ta, Mo, Ge, Sb, Sn, E3i, Ni ancd W. In general, the coercive force iHc drops with increases in temperature. However, it is possible to increase iHc at normal temperature by the addition of M, so that no 20 demagnetization would take place upon exposure to elevated temperatures. However, as the amount of ~1 increases~ there is a lowering of Br and, resulting in a lowerincJ of (BH)max, since ~l istare) a nonmaynetic elementts) ~save Ni). The M-containing alloys are very useful in recently increasing applications where higher iEIc is needed even at the price o slightly re~uced (B~J)max, providecl that tBH)max is no less :' .
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~ z77~L~9 than 2 MGOe.
To stuoy the effect of the adoition of M upon Br, experiments were conducted in varied amounts of ~l. The results are shown in ~igs. 7 and 8.
It is pre~erred to make Br no less than 3 kG so as to rnake ~BH)max equivalent to, or greater than, about 2 ~'~Oe, the level of hard ferrite. As shown in Figs. 7 and 8, the upper limits of M are as follows:
9.5 % Al, 4.7 ~ Ti, 10.5 % V, 8.5 % Cr~
8.0 % rln, 5.5 ~ Zr~ 5.5 ~ Hf, 12.5 ~ ~lb, 10.5 ~ Ta, 8.7 % Mo, 6.0 % Ge, 2.5 % Sb, 3.5 ~ Sn, 5.0 ~ Ei, 4.7 % Ni, 8.8 % W~
Wnen two or more elements M are a~ded, the resulting properties appear by way of the synthesis of the properties of the individual elements, which varies dependlng upon the proportion thereof. The amounts of the individual elements M
are within the aforesaid ranges, and the combined amount thereof is no more than the ma~imum values determlned with respect to the in~ividual elements which are actually added.
The addition or M incurs a gradual lowering of residual magnetization Br. ~ence, according to the present invention, the arnount of kl is determined such that the obtained magnets have a Br value equivalent to, or greater than, that of the conventional hard ferrite magnet~ an~ a coercive force equivalent to, or greater than. that of the convcntional products. Preferable amounts of M may be determined by selecting the amounts of ~ in wllich, e.g., Br of no less than ~: '' ' ' ,' " '" .: ' ' ' '.

4.0 kG and no less than 6.0 kG or any desired value between Br of 2-6.5 kG or higher is obtained as shown in Fiyures 7 and 8.
Fundamentally, the addition of M has an effect upon the inceease in coercive force iHc, which, in turn, increases the stability and, hence, the use of magnets.
Pre~erred is a rarlcJe of M as hereinbelow specified for obtaining Br of 4 kG or higher:
7.8 D6 Alr 3.8 % Ti~ 7.8 % V~ 6.9 % Cr, 6.9 % ~iln, 4.8 ~ Zr, 4.5 % ~f, 10.0 ~ Nb~
8.8 % Ta, 7.6 % Mo, 5.0 % Ge, 2.0 ~ Sb, 2.7 96 Sn, 4.2 % Bi~ 3.8 96 Ni~ and 7.9 % W~
wherein the same is applied when two or more of M are added.
More preferred is a range o M as hereinbelow specified for obtaining Br of 6 kG or higher:
3.4 % Al, 1.3 % Ti, 3.4 % V, 1~5 ~ Cr, 2.1 % Mn, 1.9 % Zr, 1.7 % Hf~ 2.8 ~ Nb~
3.0 % Ta, 2.8 ~ Mo, 1.6 % Ge, 0.5 % Sb, 0.7 ~ Sn, 1.9 % ~i, 1.3 % Ni~ and 3.7 % W~
wherein the same is applied when two or more of M are added.
20 The ranye of M is most preferably 0.1-3 .7 ~ to achieve (~H~max of about 7 ~IGOe, taking into cosideration the e~Eects thereof upon the increAse in iEIc and the lowering of Br as well as upon ~BEI)max. ~s ~I, V, Nbl Ta, Mo, W, Cr and ~1 are pre~erred, while a minor amount of ~1 is particuarly useful.
The rel~tionship between t~le amount of M and the coercive force has been established by way oE a wide ran~e of experiments.

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~ Z77~

- ~4 FIFTH ASPECT
According to the fifth aspect of the present invention, it is clarified that good rnagnetic properties are achieved when the FeBN~ base sintered bodies have a mean crystal grain size within a yiven constant ranye. That is, iHc of no less than 1 kOe is satisried, wllen the mean crystal grain size of t~le sintered ~odies is in a range of about 1 to about 100 r.licrons. A preferable range is 1-80 microns, and a most preferable range is 2-30 microns, wherein further enhanced iHc is obtained.
This is substantially true of the FeBP~ systems and the FeERI~ systems alike.

SIXTH ASPECT
Producing process is substantially the same as the third.aspect e~cept ~or preparation of the starting alloys or alloy powders. The additional elements M may be adde~ to the FeER base alloy(s) or rnay be prepared as FeBKll alloys. Minor amount of alloys of the constitutional elements of Fe, B, R
and M may be added to the mother alloys for Eormulating the ~inal composition.

SEVEI~TH ~SP~CT

Tile permanent magnets according to the seventh aspect of the present invention rnay permit the entrainment or the elements A in quantities in or ~elow given ~. A includes Cu~

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9L2 77~

S, C, P, Ca, ~1g, O, Si and the like. When the Fe~R and Fe~RM
base magnets are industrially prepared, such elements may often be entrained therein from the raw materials, the process of production, etc.. For instance, when FeB is used as the raw material, S and P may often be entrained. In most cases, C remains as the resiaue of organic binders (compacting-aids) used in the process of powder metallurgy. Cu is frequently contained in cheap raw materials. Ca and ~1g may easily be entrained from reducing agents. It has been observed that as lO the amount of entrained A increases, the residual magnetic flux density Br tends to drop.
As a result, when the amounts of S, C, P and Cu are no more than 2.5 %, 4.0 ~, 3.3 ~ and 3.3 %, respectively, the obtained properties (Br) are equal to, or greater than, those of hard ferrite (see Fig. 4). The allowable upper limits of O, Ca, Mg and Si are 2 %, 4.0 %, 4.0 % and 5.0 %, respectively.
When two or more elements A are entrained in the magnets, the properties of the individual elements are 20 synthesized, and the total amount thereof is no more than the maxi1num value of the values, specified above, of the actually entrained A. Within this range, Br is equal to, or greater t~1an, that of hard ferrite.
In the ca~e of the FeBRMA bac:e magnets in ~hich the isotropic permanent magnets based on FeB~ contain further A, the combined amount of ~M ~ A) is no more than the highest upper limit of the upper limits of the elements actually added , ' ' ' ' .' ' ' , ~;~77~

and entrained, as is substantially the case with two or more M
or A. This is because both ~l and A are apt to ciecrease Br.
In the case of the addition of two or more M and the entrainment oE two or more A, the resul~ing ~r property appears through the synthesis of the efEects of the individual elements upon ~r, which varies dependincJ upon the proportion thereof.
Al may be entraine~ from a refractory such as an alumina crucible into the alloys, but offers no disadantage since it is useful as M. M and A have no essential influence upon Curie point Tc, as long as they are within the presently claimed compositional range.

EXAMPLES (Fourth-Sixth Aspects) The fourth-sixth aspects of ~he present invention will now be explained in further detail with reference to examplesf ~7hich are yiven for the purpose of illustration alone, and are not intendeci to place any limitation on the invention.
Prepared were the samples based on FeE~M and FeBRE~IA
base alloys containing the given additional elements in the followiny manner.
(1) Referring to the starting materials, electrolytic iron o~ 99.9 % purity was ur~ed as Fe; Eerroboron alloys ancl boron of 99 % purity used a~ B; and Nd, Pr, Dyl Sm, Ho, Er and Ce each of 99 % purity or higher used as R ~impurities were mainly other rare-earth metals). The starting matericlls were melted by high-frecluency meltiny, and cast in a water-cooled ~7~

copper mold. ~s ~1 use was made of Ti, Mo, Bi, ~n, Sb, Ni, Ta, Sn and Ge each of 99 % purity, w of 98 % purity, Al of 99.9 %
purity, and Hf of 95 % purity. Furthermore, ferrovanadium containing ~1.2 ~ of V, ferroniobium containing 67.6 ~ of ~b, ferrochromium COntaininCJ 61.9 % of Cr and ferrozirconiwn containing 75.5 % of Zr were use~ as V, Nb, Cr and Zr, respectively.
~ 1here the elements A were contained, use was ma~e of S
of 99 ~ purity or higher, ferrophospho~us containing 26.7 % of 10 P, C of 99 % purity or hiyher, and electrolytic Cu of 99.9 %
purity or higher.
The unit of purity hereinabove is % by weight.
(2) Pulverization Coarse pulverization was carried out to 35-mesh through in a stamp mill, and fine pulverization done in a ball mill for 3 hours to 3-10 microns.
(3) Compactiny was effected under a pressure of 1.5 t/cm2.
~4) Sintering was carried out at 1000-1200 C ~or 1 hour in aryon in such a manner that the mean crystal grain size of the 20 sintered bodies came within a range o~ 5~10 rnicrons, followed by cooling down.
To investigate the magnet properties of the thus obtained samples haviny a variety of compositions, iHc, Br and ~B~I)max thereof were measured. Table 2 enumerates the permanent magnet properties, iHc, Br and (BH)max oE the typical samples. AlthoucJh not indicated numerically in the table, the balance is ~e.

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. ' ' , ~' ' Table 2 - 1 magn~ ~tic prF erties No. compositions (at %) (BH)max iHc(kOe) Br(kG) (MGOe) 1 Fe-8B-15Nd 8.5 6.4 8.7 2 Fe-8B-lONd-5Pr 5.4 4.8 4.3 3 Fe-17B-15Nd 7.2 4.8 4.6 C4 Fe-15Nd-5Al < 1 ~ 1 < 1 C5 Fe 20Nd-3W < 1 < 1 < 1 : C6 Fe-30B-15Nd-5Al < 1 < 1 < 1 C7 Fe-8B-30Nd-5Cr >10 < 1 < 1 C8 Fe-17B-5Nd-2Al-lW < 1 < 1 < 1 C9 Fe-2B-15Nd-lW 1.2 3.0 ~ 1 Fe-8B-15Nd-lTi 9.2 5.9 6.9 11 Fe-8B-lSNd-3V 9.6 4.3 3.7 12 Fe-8B-15Nd-lNb 10.0 6.1 7.9 13 Fe-8B-15Nd-0.5Nb 9.5 6.3 8.4 14 Fe-8B-15Nd-5Nb 11.0 4.4~ 3.9 Fe-8B-15Nd-2Ta 9.8 5.6 6.0 16 Fe-8B-15Nd-2Cr 10.1 4.3 3.7 17 Fe-8B-15Nd-0.5Mo 9.4 6.3 8.2 18 Fe-8B-15Nd-lMo 10.2 5.8 6.8 19 Fe-8B-15Nd-5Mo 11.0 4.2 3.5 ; ~0 Fe-8B-15Nd-0.5W Llo . 5 5.9 7.4 .

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~2771~9 Table 2 - 2 _ _ _ magnetic properties No. compositions iBc(kOe) Br(kG) (BB)max _ ,_ .
21 Fe-8B-15Nd-lW 12.3 5.8 7.0 22 Fe-8B-15Nd-SW 13.3 4.0 3.1 23 Fe-8B-15Nd-3Mn 9.O 4.3 3.7 24 Fe-8B-15Nd-3Ni 8.4 4.9 4.7 Fe-8B-15Nd-0.5Al 9.7 5.9 7.3 26 Fe-8B-15Nd-2Al 11.5 5.3 5.6 27 Fe-8B-15Nd-5Al 11.9 4.2 3.4 28 Fe-8B-15Nd-0.5Ge 8.9 5.7 6.2 29 Fe-8B-15Nd-lSn 11.8 4.7 4.4 Fe-8B-15Nd-lSb lO.l 4.6 4.1 31 Fe-8B-15Nd-lBi 10.2 5.3 5.7 32 Fe-8B-15Nd-3Ti 9.1 4.7 4.4 33 Fe-8B-15Nd-lHf 8.9 4.4 3.9 34 Fe-8B-15Nd-1.5Zr 10.3 4.7 4.3 Fe-8B-15Pr-2Mo 8.8 5.4 6.0 36 Fe-17B-15Pr-lHf-2Al 9.6 3.4 2.3 37 Fe-8B-lONd-5Pr-2Nb-2Ti 9.9 4.1 3.4 38 Fe-8B-20Nd-0.5Mo-O.SW-lTi14.0 3.6 2.5 39 Fe-8B-12Nd-3Dy-O.SNb-O.STi 9.2 4.1 3.4 Fe-lOB-14Nd-lSm-lAl-0.5W12.2 4.3 3.7 .

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~ 30 Table 2 - 3 magnetic propertles No. compositions (at %) iHc(kOe) Br(kG) (B )max _ 41 Fe~12B-lONd-5Ho-2Nb 7.5 4.7 4.2 42 Fe-7B-19Nd-SEr-lTa 11.2 5.3 5.0 43 Fe-8B-llNd-4Ce-lAl 5.3 4.9 4.8 44 Fe-lOB-15Nd-lAl-lP 8.6 4.4 3.4 45 Fe-7B-16Nd-lTi-lC 6.8 3.7 2.6 46 Fe-8B-15Nd-lW-0.SCu 3.8 5.3 5.1 47 Fe-9B-14Nd-lSi-lS 5.1 3.4 2.1 ', ':' .
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: : .

, ~ lthough the alloys containing as R Nd~ Pr, Dy and Sm are exemplified, 15 rare-earth elements tY, Ce, Sm, Eu, Tb, Dy, Er, Tm, Yb, Lu, Nd, Pr, Gd, Ho and La) show a substantially similar tendency. However, the alloys containing Nd and Pr as the main component are much more useful than those containing scarce rare earth (Sm, Y, heavy rare earth~ as the main ingredient, since rare earth ores i abound relatively with Nd and Pr and, in particular, Nd does not still find any wide use.
In Table 2, samples ~os. 4 through 9 inclusive are reference examples for the permanent magnets of the present ~ invention.
- Out of the examples of the present invention shown in Table 2, examination was made of the relationship between the coercive force iHc and the mean crystal grain size D
~microns) after sintering of Nos. 18 and 26. The results are shown in Fig. 9. Even with the same magnet, the coercive force varies depending upon the crystal grain size. Good results are obtained in a ranye of 2-30 microns, and a peak appears in a range of appro~:imately 3-10 microns.
From this, it is concluded that the gradiny of mean crystal grain sizes is required and preferred to take full advantage of the yermanent magnets of the present invention.
`; The graph oE Fig. 9 was based on the data obtained in a similar manner a5 already mentioned, provided however that the particle size of alloy powders and the crystal grain ~ize after sintering were varied.

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The permanent magnets of the present invention can be prepared with the use of commercially available materials, and it is very advantageous to use the light rare-earth elements as the key component of magnet materials. While heavy rare earth is generzlly of less industrial value clue to the fact that it is relatively rare and expensive, it m~y be used alone or in combination with light rare earth.
The increase in coercive force contributes to the stabilization of magnetic properties. Hence, the addition of M makes it feasible to obtain permanent magnets, which are substantially very stable and show a high energy product. In addition, the entrainment of the elements A within the given range offers a practical advantage in view of the industrial production of permanent magnets.
As described in detail in the foregoing, the present invention provides permanent magnets comprising magnetically isotropic sintered bodies based on FeBR, FeB~q, FeB~ and FeBR~ base alloys, whereby rnagnetic properties equal to, or greater than, those achieveci in the prior art are realized particularly without recourse to relatively rare or e~pensi~e materials. In other words, the isotropic sinterecl bodies of the present invention provide practical permanent magnets, whicll are excellent in view of re~ources, prices and magnetic properties, using as R light rare earth such as ~d ancd Pr.
Thus, the precent invention is industrially of high value.
~ odifications apparent in the art may be made without departing from the gist of the present inven~ion as disclosed and claimed:

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Claims (8)

1. A powder metallurgically sintered, isotropic permanent magnet having a mean crystal grain size of 1-80 microns and consisting essentially of, by atomic percent, 12-20 percent R wherein R is at least one element selected from the group consisting of Nd, Pr, La, Ce, Tb, Dy, Ho, Er, Eu, Sm, Gd, Pm, Tm, Yb, Lu and Y and wherein at least 50% of R consists of Nd and/or Pr, 5-18 percent B, from zero (O) percent of M to an amount of M not exceeding the atomic percentages specified below, M being selected from the group given below, wherein the sum of M does not exceed the maximum value of any one of the values specified below for M actually added, M being:
7.8% Al, 3.8% Ti, 7.8% V, 6.9% Cr, 6.9% Mn, 4.8% Zr, 4.5% Hf, 10.0% Nb, 8.8% Ta, 7.6% Mo, 5.0% Ge, 2.0% Sb,

2.7% Sn, 4.2% Bi, 3.8% Ni, and 7.9% W, and at least 62 percent Fe, in which at least 50 vol. % of the entire magnet is occupied by an Fe-B-R type ferro-magnetic compound having a substantially tetragonal crystal structure, said magnet having a maximum energy product of at least 5 MGOe and an intrinsic coercivity of at least 1 kOe.

2. A powder metallurgically sintered, isotropic permanent magnet having a mean crystal grain size of 1-80 microns and consisting essentially of, by atomic percent, 12-20 percent R wherein R is at least one element selected from the group consisting of Nd, Pr, La, Ce, Tb, Dy, Ho, Er, Eu, Sm, Gd, Pm, Tm, Yb, Lu and Y and wherein at least 50% of R consists of Nd and/or Pr, 5-18 percent B, at least one additional element M selected from the group given below in the amounts not exceeding the atomic percentages specified below, wherein the sum of M does not exceed the maximum value of any one of the values specified below for M actually added and at least 62 percent Fe:
7.8 % Al, 3.8 % Ti, 7.8 % V, 6.9 % Cr, 6.9 % Mn, 4.8 % Zr, 4.5 % Hf, 10.0 % Nb, 8.8 % Ta, 7.6 % Mo, 5.0 % Ge, 2.0 % Sb, 2.7 % Sn, 4.2 % Bi, 3.8 % Ni, and 7.9 % W, in which an Fe-B-R type ferromagnetic cornpound having a substantially tetragonal crystal structure occupies at least 50 vol % of the entire magnet, said permanent mag-net having a maximum energy product of at least 4 MGOe and an intrinsic coercivity of at least 1 kOe.

3. A magnet as defined in claim 1 or 2, in which R is about 15 atomic %, and B is about 8 atomic %.

4. A magnet as defined in claim 1 or 2, in which the amount of Si is no more than 5%.

5. A magnet as defined in claim 1 or 2, in which the sintered magnet has a mean crystal grain size of 2-30 microns.

6. A magnet as defined in claim 1 or 2, in which the sintered magnet has a mean crystal grain size of 3-20 microns.

7. A magnet as defined in claim 1 or 2, which con-tains 1 vol % or hiqher of a rare earth rich phase.

8. A magnet as defined in claim 2, in which M is one or more selected from the group consisting of V, Nb, Ta, Mo, W, Cr and Al.