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Magnetic properties of RCo4M (R-Y, Nd and Ho; M-B, Al and Ga) II
Journal of Magnetism and Magnetic Materials 104-107 (1992) 1361-1362 North-Holland
Magnetic properties of and Ga) II
RCo4M (R
H. Ido a, K. K o n n o a, T. Ito a, S.F. C h e n g
b,
= Y, Nd and Ho; M = B, A1
S.G. Sankar c and W.E. Wallace c
a Department of Applied Physics, Tohoku Gakuin University, Tagajo, Miyagi, 985, Japan b NSWC, 10901, New Hampshire At,e., Silver Spring, MD 20903-5000, USA c MEMS Department, Carnegie Mellon University, Pittsburgh, PA 15213, USA Magnetic measurements for RCo4M (M = B, Al and Ga; R = Y, Nd and Ho) have been done in order to compare the M-substitution effects on the magnetic properties of RCo 5. In the case of M = B, the crystal structure is of CeCo4B-type , while in the case of M = AI and Ga, it is of CaCus-type. By the B substitution for the Co of RCo 5 the magnetic anisotropy of the R sublattice is enhanced for R = Nd, while it seems to be weakened for R = Ho. The Co and R sublattice magnetizations and the exchange interaction between them are also discussed. T h e substitutions by B, Al a n d G a for the Co of R C o 5 have b e e n partly carried out by several a u t h o r s [1-7]. Since the e l e m e n t s B, A1 a n d G a have a similar valence electron configuration a n d at the same time B has especially a smaller atomic radius t h a n the r e m a i n ing two, it is of interest to c o m p a r e the crystallographic a n d m a g n e t i c p r o p e r t i e s of R C o 4 B with those of R C o 4 M (M = AI a n d Ga). T h e f o r m e r has b e e n known to have the C e C o 4 B - t y p e s t r u c t u r e [8], a n d the latter the CaCus-type. In this study, the m a g n e t i c p r o p e r t i e s are m e a s u r e d a n d c o m p a r e d for R = Nd a n d Ho. T h e ingots R C o 4 M ( R = Y, N d a n d Ho; M = B, A1 a n d G a ) were p r e p a r e d by melting raw materials in an arc furnace a n d t h e n a n n e a l i n g at 8 0 0 ° C for a b o u t o n e week. T h e specimens R C o 4 B , except for H o C o 4 B , have b e e n c o n f i r m e d by X-ray to be generally of a single p h a s e with t h e C e C o a B - t y p e structure, a n d R C o 4 M (M = A1 a n d G a ) of the CaCus-type. In the case of H o C o 4 B , the s p e c i m e n contains a small a m o u n t of H o 3 C O l l B 4 impurity. F i e l d - o r i e n t e d samples were p r e p a r e d by solidifying the mixtures of epoxy resin a n d the p o w d e r e d s p e c i m e n ( < 37 ixm) in a 20 k O e magnetic field at 50 ° C for H o C o a B a n d at room t e m p e r a ture for t h e o t h e r specimens. T h e t e m p e r a t u r e d e p e n d e n c e s of the s p o n t a n e o u s m a g n e t i z a t i o n s of R C o 4 M ( R = Nd a n d Ho; M = B and A1) are shown in fig. 1. N d C o 4 M (M = B a n d AI) c o m p o u n d s are f e r r o m a g n e t i c , while H o C o 4 M (M = B a n d Al) are ferrimagnetic. T h e m a g n e t i z a t i o n a n o m a l y at a r o u n d 280 K of N d C o 4 A I in fig. 1 is c o n s i d e r e d to b e associated with a spin r e o r i e n t a t i o n [2]. For H o C o a M (M = B a n d AI), the c o m p e n s a t i o n points ae o b s e r v e d a r o u n d 200 K, if we s u b t r a c t the second p h a s e c o n t r i b u t i o n from the observed curve. F r o m the o b s e r v e d s a t u r a t i o n m a g n e t i z a t i o n s at T = 0 K for H o f o 4 B a n d n o C o a A 1 , the averaged Co m o m e n t is calculated to b e 1.1/x B for b o t h cases, which is smaller t h a n 1.61xB/Co for H o C o 5 [9,10]. As seen in fig. 2, the t e m p e r a t u r e d e p e n d e n c e s of the s p o n t a n e o u s m a g n e t i -
.
100
.
.
.
80 ~ d C o 4 A [ 6o
I
00
I
i
i
~
-
100 200 300 400 500 600 -I-(K)
Fig. 1. Spontaneous magnetizations versus temperature for RCo4M.
]'0¢ ~
! YC°5 A YCo4 B YCo4A]
LX
0.8
• .dCo4B
~o~~~.o., ~ I--
•
~0.4
~
Ndsublatliee magnetization
o
ca.
Ho-sublal~ice
O.2 0
0
0.4 0.6 0.8 1.0 T /Tc Fig. 2. Relative spontaneous magnetizations versus relative temperature for YCos, YCo4B and YCo4AI. Nd- and Hosublattice magnetizations, experimental and calculated (solid curves), are also plotted (see text).
0312-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
0.2
1362
H. ldo et al. / Magnetic properties
of RCo4M
20 HoCo~ B
titted i ptonar
15
~ l
axial
i i i
..-....
&E I O ©
3owder (H=0.1kOe)
%
NdCo 5 NdCo4A1 NdCo4B HoCo 5 HoCo4A1 HoCo4B
fU/A ,
:ieLdaligned sample (H :1 kOe) H//c-axis i
0
0 L
I
100
,
I
200
,
I,
300
,
I
400
,
500
i
100
200 300 400 T(K) Fig. 3. Temperature dependence of magnetization of HoCo4B measured along the easy direction of magnetization. A tilted state exists between T = 266 and 310 K.
zations of Y C o s [9], Y C o 4 B [11] and Y C o 4 A I [11], which are expressed by the n o r m a l i z e d form, are similar to each other, so this f e a t u r e will be conserved also in R C o 4 M ( R = Nd, Ho; M = B, AI), c o n s e q u e n t l y we can e s t i m a t e d the R sublattice m a g n e t i z a t i o n , which is plotted against t e m p e r a t u r e for R = Nd a n d H o tog e t h e r with the calculated curves b a s e d on the molecular field theory [12]. T h e calculation gives us the exc h a n g e interaction J R _ c o / k is a b o u t 7 K for N d C o 4 B (M = B a n d A1) a n d a b o u t 8.5 K for H o C o 4 B . T h e s e values are in good a g r e e m e n t with those o b t a i n e d by Burzo et al. [4]. T h e r o u g h estimation of JR-Co did not give us a significant difference b e t w e e n the two cases of M = A1 and M = B. As seen in fig. 3, the t e m p e r a ture d e p e n d e n c e of the m a g n e t i z a t i o n of H o C o n B under the m a g n e t i c field H = 1 k O e (lie-axis) shows a spin r e o r i e n t a t i o n in the o r d e r of p l a n a r ~ tilted axial, with increasing t e m p e r a t u r e . By m e a s u r e m e n t s similar to those in fig. 3, we d e t e r m i n e d the spin r e o r i e n t a t i o n t e m p e r a t u r e s for some o t h e r cases as s u m m a r i z e d in fig. 4. In the case of N d C o 5, the substitution effect by B is significant, which is explained by the increase of p l a n a r anisotropy of the Nd sublatticc as well as the d e c r e a s e of the Co sublattice axial anisotropy by the B substitution. In the case of SmCo 5, the Sm sublattice anisotropy seems to be e n h a n c e d in S m C o 4 B from that of SmCo 5 [6]. However in the case of H o C % , t h e r e is no significant difference b e t w e e n the spin r e o r i e n t a t i o n p h e n o m e n a of H o C o s and H o C o 4 B . T h e m a g n e t i c anisotropy c o n s t a n t K 1 of Y C o 4 B at 300 K is 0.03 × 107 e r g / c c [2,12], which is smaller by far than t h a t of Y C o 5, t h e r e f o r e to explain the o c c u r r e n c e of the spin r e o r i e n t a t i o n of H o C o 4 B , the H o sublattice p l a n a r anisotropy of H o C o s also must be d e c r e a s e d by the B substitution, contrary to
T(K) Fig. 4. Effect of the A1 and B substitutions on the spin reorientation of RCo 5 compounds (R = Nd and Ho). The data for RC% are taken from refs. [13 15]. the cases of N d C o 4 B a n d SmCo4B. It seems t h a t the B substitution weakens the R sublattice anisotropy of R C o 5 in the case of R = heavy rare earth. References
[1] I. Shidlovsky and W.E. Wallace, J. Solid State Chem. 2 (1970) 193. [2] H. Ido, K. Konno, S.F. Cheng, W.E. Wallace and S.G. Sankar, J. Appl. Phys. 67 (1990) 4638. [3] A.T. Pedziwiatr, S.Y. Jiang, W.E. Wallace, E. Burzo and V. Pop, J. Magn. Magn. Mater. 66 (1987) 69. [4] E. Burzo, N. Plugaru, I. Crenga and M. Ursu, J. LessCommon Met. 155 (1989) 281. [5] H.H.A. Smit, R.C. Thiel and K.H.J. Buschow, J. Phys. F 18 (1988) 295. [6] H. Oesterreicher, F. Spada and C. Abacbe, Mater. Res. Bull. 19 (1984) 1069. [7] H. Ido, W.E. Wallace, T. Suzuki, S.F. Cheng, V.K. Sinba and S.G. Sankar, J. Appl. Phys. 67 (1990) 4635. [8] Yu. B. Kuzuma and N.S. Bilonizhko, Sov. Phys. Crystallogr. 18 (1974) 447. [9] T. Okamoto, H. Fujii, C. Inoue and E. Tatsumoto, J. Phys. Soc. Jpn. 34 (1973) 835. [10] J.J. Velge and K.H.J. Buschow, J. Appl. Phys. 39 (1968) 1717. [11] H. Ido, K. Konno, S.F. Cheng, S.G. Sankar and W.E. Wallace, Proc. 6th Int. Symp. on Magn. Anisotropy and Coercivity in RE-Transition Metal Alloys, Vol. 2, ed. S.G. Sankar (Pittsburgh, USA, 1990) p. 80. [12] H. Ido, K. Konno, T. Ito, S.F. Cheng, S.G. Ssnkar and W.E. Wallace, J. Appl. Phys. to be published (35th Annual Conf. on 3M, San Diego, 1990). [13] A.S. Ermolenko, IEEE Trans. Magn. Mag-12 (1976) 992. [14] E. Tatsumoto, T. Okamoto, H. Fujii and C. Inoue, J. de Phys. C1 (1970) 551. [15] B. Decrop, J. Deportes and R. Lemaire, J. Less-Common Met. 94 (1983) 199.
Magnetic properties of and Ga) II
RCo4M (R
H. Ido a, K. K o n n o a, T. Ito a, S.F. C h e n g
b,
= Y, Nd and Ho; M = B, A1
S.G. Sankar c and W.E. Wallace c
a Department of Applied Physics, Tohoku Gakuin University, Tagajo, Miyagi, 985, Japan b NSWC, 10901, New Hampshire At,e., Silver Spring, MD 20903-5000, USA c MEMS Department, Carnegie Mellon University, Pittsburgh, PA 15213, USA Magnetic measurements for RCo4M (M = B, Al and Ga; R = Y, Nd and Ho) have been done in order to compare the M-substitution effects on the magnetic properties of RCo 5. In the case of M = B, the crystal structure is of CeCo4B-type , while in the case of M = AI and Ga, it is of CaCus-type. By the B substitution for the Co of RCo 5 the magnetic anisotropy of the R sublattice is enhanced for R = Nd, while it seems to be weakened for R = Ho. The Co and R sublattice magnetizations and the exchange interaction between them are also discussed. T h e substitutions by B, Al a n d G a for the Co of R C o 5 have b e e n partly carried out by several a u t h o r s [1-7]. Since the e l e m e n t s B, A1 a n d G a have a similar valence electron configuration a n d at the same time B has especially a smaller atomic radius t h a n the r e m a i n ing two, it is of interest to c o m p a r e the crystallographic a n d m a g n e t i c p r o p e r t i e s of R C o 4 B with those of R C o 4 M (M = AI a n d Ga). T h e f o r m e r has b e e n known to have the C e C o 4 B - t y p e s t r u c t u r e [8], a n d the latter the CaCus-type. In this study, the m a g n e t i c p r o p e r t i e s are m e a s u r e d a n d c o m p a r e d for R = Nd a n d Ho. T h e ingots R C o 4 M ( R = Y, N d a n d Ho; M = B, A1 a n d G a ) were p r e p a r e d by melting raw materials in an arc furnace a n d t h e n a n n e a l i n g at 8 0 0 ° C for a b o u t o n e week. T h e specimens R C o 4 B , except for H o C o 4 B , have b e e n c o n f i r m e d by X-ray to be generally of a single p h a s e with t h e C e C o a B - t y p e structure, a n d R C o 4 M (M = A1 a n d G a ) of the CaCus-type. In the case of H o C o 4 B , the s p e c i m e n contains a small a m o u n t of H o 3 C O l l B 4 impurity. F i e l d - o r i e n t e d samples were p r e p a r e d by solidifying the mixtures of epoxy resin a n d the p o w d e r e d s p e c i m e n ( < 37 ixm) in a 20 k O e magnetic field at 50 ° C for H o C o a B a n d at room t e m p e r a ture for t h e o t h e r specimens. T h e t e m p e r a t u r e d e p e n d e n c e s of the s p o n t a n e o u s m a g n e t i z a t i o n s of R C o 4 M ( R = Nd a n d Ho; M = B and A1) are shown in fig. 1. N d C o 4 M (M = B a n d AI) c o m p o u n d s are f e r r o m a g n e t i c , while H o C o 4 M (M = B a n d Al) are ferrimagnetic. T h e m a g n e t i z a t i o n a n o m a l y at a r o u n d 280 K of N d C o 4 A I in fig. 1 is c o n s i d e r e d to b e associated with a spin r e o r i e n t a t i o n [2]. For H o C o a M (M = B a n d AI), the c o m p e n s a t i o n points ae o b s e r v e d a r o u n d 200 K, if we s u b t r a c t the second p h a s e c o n t r i b u t i o n from the observed curve. F r o m the o b s e r v e d s a t u r a t i o n m a g n e t i z a t i o n s at T = 0 K for H o f o 4 B a n d n o C o a A 1 , the averaged Co m o m e n t is calculated to b e 1.1/x B for b o t h cases, which is smaller t h a n 1.61xB/Co for H o C o 5 [9,10]. As seen in fig. 2, the t e m p e r a t u r e d e p e n d e n c e s of the s p o n t a n e o u s m a g n e t i -
.
100
.
.
.
80 ~ d C o 4 A [ 6o
I
00
I
i
i
~
-
100 200 300 400 500 600 -I-(K)
Fig. 1. Spontaneous magnetizations versus temperature for RCo4M.
]'0¢ ~
! YC°5 A YCo4 B YCo4A]
LX
0.8
• .dCo4B
~o~~~.o., ~ I--
•
~0.4
~
Ndsublatliee magnetization
o
ca.
Ho-sublal~ice
O.2 0
0
0.4 0.6 0.8 1.0 T /Tc Fig. 2. Relative spontaneous magnetizations versus relative temperature for YCos, YCo4B and YCo4AI. Nd- and Hosublattice magnetizations, experimental and calculated (solid curves), are also plotted (see text).
0312-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
0.2
1362
H. ldo et al. / Magnetic properties
of RCo4M
20 HoCo~ B
titted i ptonar
15
~ l
axial
i i i
..-....
&E I O ©
3owder (H=0.1kOe)
%
NdCo 5 NdCo4A1 NdCo4B HoCo 5 HoCo4A1 HoCo4B
fU/A ,
:ieLdaligned sample (H :1 kOe) H//c-axis i
0
0 L
I
100
,
I
200
,
I,
300
,
I
400
,
500
i
100
200 300 400 T(K) Fig. 3. Temperature dependence of magnetization of HoCo4B measured along the easy direction of magnetization. A tilted state exists between T = 266 and 310 K.
zations of Y C o s [9], Y C o 4 B [11] and Y C o 4 A I [11], which are expressed by the n o r m a l i z e d form, are similar to each other, so this f e a t u r e will be conserved also in R C o 4 M ( R = Nd, Ho; M = B, AI), c o n s e q u e n t l y we can e s t i m a t e d the R sublattice m a g n e t i z a t i o n , which is plotted against t e m p e r a t u r e for R = Nd a n d H o tog e t h e r with the calculated curves b a s e d on the molecular field theory [12]. T h e calculation gives us the exc h a n g e interaction J R _ c o / k is a b o u t 7 K for N d C o 4 B (M = B a n d A1) a n d a b o u t 8.5 K for H o C o 4 B . T h e s e values are in good a g r e e m e n t with those o b t a i n e d by Burzo et al. [4]. T h e r o u g h estimation of JR-Co did not give us a significant difference b e t w e e n the two cases of M = A1 and M = B. As seen in fig. 3, the t e m p e r a ture d e p e n d e n c e of the m a g n e t i z a t i o n of H o C o n B under the m a g n e t i c field H = 1 k O e (lie-axis) shows a spin r e o r i e n t a t i o n in the o r d e r of p l a n a r ~ tilted axial, with increasing t e m p e r a t u r e . By m e a s u r e m e n t s similar to those in fig. 3, we d e t e r m i n e d the spin r e o r i e n t a t i o n t e m p e r a t u r e s for some o t h e r cases as s u m m a r i z e d in fig. 4. In the case of N d C o 5, the substitution effect by B is significant, which is explained by the increase of p l a n a r anisotropy of the Nd sublatticc as well as the d e c r e a s e of the Co sublattice axial anisotropy by the B substitution. In the case of SmCo 5, the Sm sublattice anisotropy seems to be e n h a n c e d in S m C o 4 B from that of SmCo 5 [6]. However in the case of H o C % , t h e r e is no significant difference b e t w e e n the spin r e o r i e n t a t i o n p h e n o m e n a of H o C o s and H o C o 4 B . T h e m a g n e t i c anisotropy c o n s t a n t K 1 of Y C o 4 B at 300 K is 0.03 × 107 e r g / c c [2,12], which is smaller by far than t h a t of Y C o 5, t h e r e f o r e to explain the o c c u r r e n c e of the spin r e o r i e n t a t i o n of H o C o 4 B , the H o sublattice p l a n a r anisotropy of H o C o s also must be d e c r e a s e d by the B substitution, contrary to
T(K) Fig. 4. Effect of the A1 and B substitutions on the spin reorientation of RCo 5 compounds (R = Nd and Ho). The data for RC% are taken from refs. [13 15]. the cases of N d C o 4 B a n d SmCo4B. It seems t h a t the B substitution weakens the R sublattice anisotropy of R C o 5 in the case of R = heavy rare earth. References
[1] I. Shidlovsky and W.E. Wallace, J. Solid State Chem. 2 (1970) 193. [2] H. Ido, K. Konno, S.F. Cheng, W.E. Wallace and S.G. Sankar, J. Appl. Phys. 67 (1990) 4638. [3] A.T. Pedziwiatr, S.Y. Jiang, W.E. Wallace, E. Burzo and V. Pop, J. Magn. Magn. Mater. 66 (1987) 69. [4] E. Burzo, N. Plugaru, I. Crenga and M. Ursu, J. LessCommon Met. 155 (1989) 281. [5] H.H.A. Smit, R.C. Thiel and K.H.J. Buschow, J. Phys. F 18 (1988) 295. [6] H. Oesterreicher, F. Spada and C. Abacbe, Mater. Res. Bull. 19 (1984) 1069. [7] H. Ido, W.E. Wallace, T. Suzuki, S.F. Cheng, V.K. Sinba and S.G. Sankar, J. Appl. Phys. 67 (1990) 4635. [8] Yu. B. Kuzuma and N.S. Bilonizhko, Sov. Phys. Crystallogr. 18 (1974) 447. [9] T. Okamoto, H. Fujii, C. Inoue and E. Tatsumoto, J. Phys. Soc. Jpn. 34 (1973) 835. [10] J.J. Velge and K.H.J. Buschow, J. Appl. Phys. 39 (1968) 1717. [11] H. Ido, K. Konno, S.F. Cheng, S.G. Sankar and W.E. Wallace, Proc. 6th Int. Symp. on Magn. Anisotropy and Coercivity in RE-Transition Metal Alloys, Vol. 2, ed. S.G. Sankar (Pittsburgh, USA, 1990) p. 80. [12] H. Ido, K. Konno, T. Ito, S.F. Cheng, S.G. Ssnkar and W.E. Wallace, J. Appl. Phys. to be published (35th Annual Conf. on 3M, San Diego, 1990). [13] A.S. Ermolenko, IEEE Trans. Magn. Mag-12 (1976) 992. [14] E. Tatsumoto, T. Okamoto, H. Fujii and C. Inoue, J. de Phys. C1 (1970) 551. [15] B. Decrop, J. Deportes and R. Lemaire, J. Less-Common Met. 94 (1983) 199.