their huge values of Kui (R = Pr, Tb and Dy) or negligible ... Kui was calculated using .... 3) J. J. Croat, J. F. Herbst, R. W. Lee and F. E. Pinkerton: J. Appl. Phys.
JAPANESE JOURNAL OF APPLIED PHYSICS VOL.24,No.10,OcToBER,1985,pp.L803-L805
Single Crystal Mcasurements of Anisotropy Constants of R2Fe14B(R=Y,Ce,Pr,Nd,Gd,Tb,Dy and Ho) Satoshi HIROSAWA,Yutaka N/1ATSUURA,HitOshi YAMAMOTO, Setsuo FuJIMuRA,NIaSato SAGAWA and Hiroshi YAMAUCHI十
―ノ7ど gαWα,S乃 デ r77α 777θ ど θC力ο,Osα たαび′8 ′ S2777F irθ ″οsβcC'α ′Merαな Cο.二rび.,2-FD‐ 1 沢岱g ″ 2 パ′ 予 石θ rα な, 「θt t ο た″t / r ソ が r c 力r 7 r s rι Frrgと yθ / r rθ ・れ, s r g t t 々 どO r ヵg / ソ α ゥ, 2-7-′ 【αrα ん,メ α, sc沌びα'98θ (Rcccivcdフヘugust 12, 1985;acccptcd for publication Scptcmbcr 28, 1985)
Thc nrst order anisotropy constantsス ru1 0f thc rcccntly found tctragonal rarc carth iron boridcs R2Fc14B(P42/mnlll) havc bccn mcasured for R=Y,Cc,Pr,Nd,Gd,Tb,Dy and Hoin a magnctic ncld up t0 1600 kA/m from 4.2 K to ab 600 K on single crystal samples.
in epoxy rcsin and thc cpoxy、vas then machincd into 3 Hlrll cubcsc One of thc cdgcs of cach cubc 、 vas kcpt
Rarc carth― iron borides R2Fe14B,WhCrc R stands for rarc earths including Y, havc rccicvcd much attentlon
axis of thc compound. parallel to the c― In ref。 (I), the anisotropy neld 、vas deflned as a to hold thc flctitious rnagnetic tlcld acting along axis the c― vas cstilmated agnctization in that direction.Its valuc、 中
sincc Nd2Fc14B WaS identiflcdl)to bc the major hard Fc一B pcrmancnt magnetic magnctic phase in the Nd一 matcrials.2,3)Numerous studics havc becn undcrtakcn in rccent years to invcstigatc both thc basic properties of thc of R2Fc14B COmpounds and the origin and thc rncchanisl■
using
coercivity of the R一 Fe一B magnets.Nlteasurements of the
ダA=(ム/r上 ス, )rfO ハ
basic magnetic properties have been reportcd on both polycrystalline4 7)and Singlc― crystalline spccilncns.812) Thc single― crystal studics by Givord g″ α′ .,8)saga、va gr va and Iirosa、 .,10)Koon er α′ .,11)and I― α′ .,9)Hiroyoshi gr α′
(1)
、 vhcrc tt and rtt arc the saturation magnetization and magnetization measurcd in an cxtcrnal fleld FfO applicd /is the perpendicular to thc c― axis, rcspectively, andハ
Saga、va12)arOrdcd more accuratc and dctailcd rcsults than the polycrystal studics.Ho、 vcvcr,the entirc scrics of va thc compound has not bccn coveredi Reccntly,Hirosa、
demagnctization factor,Forthc Nd and]=o compounds, VhiCh iS thc easy dircction ア上 WaS Ineasurcd along[110]ヽ of magnetization in the basal planc. For othcr coln― gr ′ α . p r c p a r e d s i n g l e c r y s t a l s o f R 2 F c 1 4 B W i t h R =pounds,anisotropy Y,Cc, vas not dctected in in the basal plane、 Pr,Nd,Sm,Gd,Tb,Dy,Ho,Erand Tm,and mcasured SN/1 becallse of either the rangc of rfO availablc in ourヽ 〆 saturation rnagnetizations and anisotropy nelds of these compounds.The detailcd results of this study have been submitted elsewherc(hereafter rcfFcrcd as ref.(I)).*In ref。(I),hOヽVever,values of the anisotropy constants'て
their hugc values ofttrul(R=Pr,Tb and Dy)or negligiblc 【u 3 V a l u e s ( R = Y , C e a n d G d ) . 【u l W a s c a l c u l a t e d u s i n g ul
【ul=(1/2)兵 ダA・
(2)
verc not reportcd. and thcir tempcrature dependence 、 Bccause theoretical investigatiolls arc currently in pro―
V a l u e s o f t t a n d r f A a r C t h e s a H l c a s r c p o r t c d i n( I r) c f 。 and are sho、vn in thc Appendix for readers'convenience.
gress to elucidatc various behaviors of magnctocrystallinc anisotropy of thcsc compounds,the ful valucs and qucst for a precise mcasuremcnt of thcム
The authors believe that the valucs for】
てul obtained in rfO curvcs are this proccdure arc reliablc,bccausc thc r上 straight in the range of cxtcrnal ncld invcstigatcd, in 、 vhich contributions of thc highcr ordcr anisotropy con― stants スfu2 and ス ru3 0n the magnctization curvcs are
thcir tempcraturc depcndcncc has incrcascd. In this rcgard, thc present lctter reports thc temperature ful of R2Fc14B WhiCh has uniaxial dcpcndencc of ス
thcrcforc ncgligiblc,cxccpt for thc cases of Nd2Fe14B and a n i s o t r o p y a t r o o m t e n l p c r a t u r c f o r R = Y , C c , P r , G H02Fc14B d, at 10w tclnperatures wherc spin reorientation Tb, Dy and Ho. Results for compounds with planar transitions takc placc(see bC10W). anisotropy, narnely, for R=Sm, Er and Tm, wcre V thC temperaturc dcpendence Figures l(a)and(b)ShOヽ vhere.10'12) rcported else、 Ofスrul calculated fron■cq.(2).Despite the hugc values of The proccdure for sample preparation was also dcscrib― ul Values ofthese corn― 払 Of Tb2Fe14B and Dy2Fe14B,thC【 A vibrating sample magnetometer(VSM) ed earlier.10'1り pounds are reduced bccause of thc compounds' small cquipped with an elcctromagnet capablc of a 1200 kA/m magnetization. In contrast, Pr2Fe14B pOsscsses a huge maximurn tlcld 、 vas used for magnctic measurcmcnts value ofス rul at 10w temperatures(Fig。 1(b)),aS Can be cx― above 77 K.For lncasurcments at lo、 vcr temperaturcs,a pected from the large ncgativc valucs of thc second ordcr VSNI at the Rcscarch lnstitutc for lron,Stccl and Other vas uscd, Sphcrically NIctals, Tohoku Univcrsity, 、 shapcd single crystals typically of 10 1ng、vcrc cmbcdded
S t e v c n s c o e f n c i c n tJ (α T a b l c l ) . T h C r a p i d d c c r c a s c o fu 【 l Of Pr2Fe14B Can bc attributcd to the weak Pr一 Fc cxchange intcractions,、vhich lead to a rapidly incrcasing thermal disordcr in the Pr sublattice as tempcraturc incrcases.An attempt to evaluatc the temperaturc dcpcndencc of the magnetocrystallinc anisotropy of the rare earth sublat"
ネs.Hirosawa,Y.Matsuura,H.Yamamoto,S.Fujimura)M.Sagawa .Appl.Phys.(rCCCivcd Junc 10, and H.Yamauchi:submitted to」 1985). L803
L804
S.HIROSAWA,Y.MATSUURA,H.YAMAMOTO,S.FuJIMuRA,N4t`SAGAWA and H.YAMAUCHI
Tablc l. Anisotropy constant Kut of R2Fc14B at 4.2 K and thc second ordcr Stcven factors α」ofthc R+3 ionS.13)
ョ Ｚく ︵”Ｅ ヽ﹁こ ︶﹁ ︼ 卜Ｚ く卜のＺ０ ０ ＞ＬＯ α卜０り一
Compound
馬 1(J/M3)
Y2Fc14B
0 . 7 7 ×1 0 6 1 . 6 5 ×1 0 6 2.35X107 -1.6× 107*
Ce2Fc14B Pr2Fc14B Nd2Fc14B
0 - 5 . 7 1 4 ×1 0 2 - 2 . 1 0 1 ×1 0 2 4 . 1 2 7 ×1 0 2 4 . 1 2 7 ×1 0 2
Sr12Fe14B
2 . 6 ×1 0 7 1 0 )
Gd2Fc14B Tb2Fe14B
0.72X106 8 . 2 ×1 0 6
0 - 1 . 0 1 0 ×1 0 2
Dy2Fc14B
38X106
-6.349×103 - 2 . 2 2 2 ×1 0 3
H02Fe14B
*H.Yamauchi:in prcparation.
dcpendcnce ofス
ご 口 l comcs froIIa changcs in band splitting
ofthe Fe 3d band. Attempts at an empirical clariflcation of this problem 300
400
are currently being madc in our laboratory.
TEMPERATURE(K)
Ce2Fc14B falls in the same catcgory as the Y and Gd compounds as far asthe"て ul Valuc is conccrncd.Cc+3 haS a larger α J valuc than Pr+3(Table I)and WOuld give a てui value clcarly in― vcry largc anisotropy.The obscrved」
R2Fe14B
dicates that Cc in Ce2Fe14El is csscntially tetravalcnt,
Pr(Kul× 10-1)
、 vhich is also suggested frorn thc anomalously small lat― 4,5)Thc largcr value ofス ful and ticc constants of Ce2Fe14B。
ョ ︵”Ｅ ヽ﹁〓 ▼ ︼
TEMPERATURE(K) Fig. 1. (a)Tcmperature dcpcndencc of thc anisotropy constantプ
ζul of rul
R2Fc14B。 (b)TCmpcrature depcndencc or thc anisotropy constantス For Pr2Fc14B,theて of Y2Fc14B,CC2Fe14B,Gd2Fe14B and Pr2Fc14B・
︵Ｄ﹂ヽロミ ︶ Ｚ Ｏ 一 卜くＮ〓 トロＺ り く 〓
式主 ＼ ＼
ul
valucs are rcduccd by a Factor of ten in(b).
tices was made in rcf。 (I)using a simplined mOlecular ield approxilnation. When the rare earth sublattice does not contribute to thc lnagnetocrystallinc anisotropy,the compounds sho、 v cssentially thc same charactcristics of the tcrnperature dependcncc of」 てul:」 《ul、vhich has a broad maxiFnum at
R2Fe14B
around r=0,67L as iS dCpicted in Fig, 1(b).ThC Origin of this peculiar thcrrnal variation ofス rulis not clcar at prc― sent.T、vo altcrnativc cxplanations are possible. (1) Anisotropy competition: thcrc arc six une― quivalcnt Fe sitcs,1)some Of、vhich may havc negativc con― tributions to」てul and larger terllpcrature dcpcndcnces of sublattice magnetizations than other Fe sites 、 vith positive contributions to」てul.Thc negativc contributions v tcmperaturcs and lead to a decrease inス 名l as arise at lo、
｀ 20 ミ 0
望 10 0 こ
temperature decreases. (2) Band efFects:thc anisotropy ofthe Fe sublatticc is
TEMPERATURE(K)
弱c面 allj7 ned dder面 by band cttdtt whch普 H&2負 t h e s p i no―r b i t c o u p l i n g o f t h e 3 d e l c c t r o n s 群 a n cfi:鮮 蟹 艦密撤n鷲 :[ぜ 拙骨 濫 猟n菅 路aぱ 瑠:laだ (群 14ぎ sitive to thc position of thc Fcrrni lcvel.The ternperature
and(b):heaVy rare earth compounds.
r R2Fc14B /4″なο力・ Э py Cο ″srα輝な て り
verくOurie temperaturc4,5)。 f the Cc2Fe14B COmparcd a lo、 to thosc of Y2Fc14B and Gd2Fe14B IInay be rclatcd to fur― thcr f11ling of the 3d band duc to thc tctravalcncy of thc Ce lons.This、 vould support cxplanation(2)above COn_ ccrning the origin of the tcmperaturc of thc magnetocrystallinc anisotropy of the Fe sublattice in R2Fc14B・ HOWcver,therc is a possibility that Cc is partial― ly trivalent
and
has
some
contributlon
to
H02Fc14B｀
L805
Vith decreasing temperature is related to spin
reoricntation transitions(SRTs)whiCh take place at about 150 K and 60 K, rcspcctivcly for thc Nd and Ho compounds. A dctailed experilncntal study concerning thcsc phenomena is dcscribcd i1l rcf.(I), tOgcthcr、
vith
SRTs in Er2Fc14B and Tm2Fc14B, Appendix
the
magnctocrystallinc anisotropy.An cmpirical dctcrIIlina…
For rcadcrs'convenicncc,thc tcrllpcraturc depcndcnce
tion ofthc valcncy ofthe Ce lonsin Cc2Fc14B may bc of intcrest. Thc anomalous decrcasc in て ul of Nd2Fc14B and
of the saturation rllagnctization and anisotropy llelds of thc R2Fe14B COmpounds rcported in ref。
(I)arc ShOWn in
Figs。 (2)and(3),respectivcly, References
24
R2Fe14B
MA/m 20
︵ｏＯ ︼︶ Ｏ Ｊ口 一 ﹂
16
Ｚく ＞Ｌ Ｏ Ｅ 卜０ り ”
12
8
4
▼ 0
100
200
31111
400
51X1
6tX1
705
TEMPERATURE(K) Fig。3.
Tcmpcraturc dcpendcncc of anisotropy flclds of R2Fc14B
measured in an applicd ield of 800 kA/m`
B.Yeloni Phys. l) J.F.Hcrbst,J.J.Croat,F.E.Pinkerton and Yぅ Rev.B29(1984)4176. 2)M.Sagawa,S.Fujimura,N.Togawa,H.Yamamoto and Y. Matsuura:J.Appl.Phys.55(1984)2083. ア .Lee and F.E.Pinkcrton:J.Appl. 3)」 :J.CrOat,J.F.Hcrbst,R.恥 Phys.55(1984)2078. 4) S.Sinncma,R.」 .Radwanski,J.J.M.Fransc,D.B.de Mouji and K.H.J.Buschow:J.Magn.Magn.Matcr.45(1984)333. 5)H.Yamamoto,Y.Matsuura,S.Fujimura alld M.Sagawa:Appl` Phys.Lett,45(1984)1141. ア .E. 6) E.B.Boltich,E.Oswald,M.Q.Huang,S.Hirosawa and恥 ヽ/allcc:J.Appl,Phys.57(1985)4106. 7)C.Abache and H.Oestcricher:」 .Appl.Phys.57(1985)4112. 8)D.Givord,H.S.Liand R.Pcrricr dc la Bathiei solid State Com― mun.51(1984)857. 9)M.Sagawa,S.Fujimura,H.Yamamoto,Y.Matsuura and S. Hirosawa:」 .Appl.Phys.57(1985)4094. 10)H.HirOyoshi,H.Yamauchi,H.Yamamoto,Y.Nakgawa and M. Sagawai Solid Statc Comnlun.54(1985)41. 11)N.C.Koon,B.N.Das,NI.Rubinstcin and J.Tyson:J.Appl. Phys.57(1985)4091. 12) S.HirOSawa and NI.Sagawa:Solid State C ollllnun.54(1985)335. 13)K.ヽ V.H.Stevcnsi Proc,Phys.Soc.A65(1952)209.
