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Sublattice anisotropy constants of Dy2Fe14B and Tb2Fe14B at 4.2 K
Journal of Magnetism and Magnetic Materials 189 (1998) 251—254
Sublattice anisotropy constants of Dy Fe B and Tb Fe B 2 14 2 14 at 4.2 K Y.B. Kim*, Han-min Jin1 Korea Research Institute of Standards and Science, P.O. Box 3, Taedok Science Town, Taejon 305-600, South Korea Received 3 April 1998; received in revised form 19 May 1998
Abstract The rare-earth sublattice anisotropy of Dy Fe B and Tb Fe B at 4.2 K have been analyzed by semi-graphical 2 14 2 14 method on the bases of two sublattice model. The anisotropy constants of Dy-sublattice are determined as K " 1D: 1600 J/kg and K "6600 J/kg, and the constant of Tb-sublattice as K "4300 J/kg. The magnetizations calculated 2$: 1T" by energy minimum method by applying the sublattice anisotropy constants reproduced well the experiments and satisfied the simulation assumptions. ( 1998 Elsevier Science B.V. All rights reserved. PACS: 75.30.Gw; 75.70.Vv; 75.50.Ww Keywords: Magnetocrystalline anisotropy; Sublattice anisotropy; Rare-earth—3d transition metal compounds
1. Introduction NdFeB alloy [1,2] shows excellent hard magnetic properties and is widely used as the raw material for the high-coercive high-energy permanent magnets. The high coercivity is originated from the strong uniaxial magnetocrystalline anisotropy of Nd Fe B at room temperature [3]. 2 14
* Corresponding author. Fax: #82 42 868 5018; e-mail: [email protected]. 1 Guest scientist from Jilin University, Changchun, P.R. China. Supported by the Brain Pool Project of the Korean Federation of Science and Technology Societies.
Dy Fe B [4] and Tb Fe B [4] are known to 2 14 2 14 have much stronger anisotropy than Nd Fe B, 2 14 and Dy or Tb are added to increase the coercivity of NdFeB-type magnets. The magnetocrystalline anisotropy of Dy Fe B and Tb Fe B may be 2 14 2 14 understood to some extent from their crystalline electric field (CEF) parameters [5—7], because the anisotropy constants can be calculated [6] from the CEF parameters. The exact calculation, however, is only possible when the magnetic moments of rareearth and Fe sublattices are colinear which may occur near room temperature. At low temperature near 4.2 K, the sublattice moments are usually non-colinear due to the strong magnetocrystalline anisotropy of rare-earth sublattice, and the
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anisotropy constants cannot be deduced from CEF parameters. Recently, the authors have suggested the graphical methods [8,9] to analyze the anisotropy of uniaxial magnetocrystalline anisotropy system. The methods are simple and give the anisotropy constants directly from magnetization curves of magnetization easy or hard direction within hard magnetization plane. Dy Fe B and Tb Fe B 2 14 2 14 show uniaxial magnetocrystalline anisotropy below their Curie temperatures. In this paper, we report the anisotropy constants of rare-earth sublattice of the compounds analyzed by the semigraphical method.
2. Analysis results The rare-earth elements in R Fe B-type 2 14 (R"rare-earth elements) compounds occupy crystallographically different f and g sites [10]. Though the rare-earth moments occupy the different sites, treating them as one sublattice resulted in a good approximation [9] in analyzing the anisotropy constants of rare-earth sublattice. Dy Fe B and Tb Fe B show the uniaxial 2 14 2 14 magnetocrystalline anisotropy with easy magnetization tetragonal c-axis at 4.2 K. If we assume the compounds as a two sublattice system of Fe and rare-earth moment, and every moments to rotate on the plane made by H and c-axis [8,9], the free energy of the system in a magnetic field parallel to [1 0 0] or [1 1 0] direction is expressed as follows: E"K sin2 h #K sin2 h 1F% F% 1R R #(K $K )sin4 h #(K $K )sin6 h 2 2R 3R R 4R 5R R !M H sin h !M H sin h F% F% R R #N M M (sin h sin h RF% F% R F% R #cos h cos h ). (1) F% R Here, the notation h implies the inclination angle of sublattice moments from the [0 0 1] axis. The anisotropy of Fe-sublattice is assumed to have the first order only and the constant is expressed as K . K (i"1,2,2,) is the ith anisotropy con1F% iR stant of rare-earth sublattice. M and M are the F% R
magnetizations of Fe and rare-earth sublattice, respectively. N is the macroscopic exchange RF% interaction coefficient between rare-earth and Fe sublattices, which is well defined in Ref. [11], and is treated in Eq. (1) as positive for antiferromagnetic coupling. The $ sign of K and K becomes 3R 5R positive when H is parallel to [1 0 0] and negative when H is parallel to [1 1 0]. If we define the magnetizations observed in field direction as m and the contribution of Fe and rare-earth sublattice as m and m , respectively, we F% R can obtain the following relations from the equilibrium condition of free energy.
G
m!m m m!m R!M H#N M M R! R 2K 1F% M F% RF% F% R M M F% R F%
H
!J1!(m /M )2 R R "0, J1!(m!m )2/M2 F% R
(2)
A B A B
m 3 m R #4 R (K $K ) 2K 2R 3R 1RM M R R #6
m 5 R (K $K )!M H 4R 5R R M R
G
m F% #N M M RF% F% R M F%
H
m J1!(m /M )2 F% F% ! R "0. M !J1!(m /M )2 R R R
(3)
If we know the values of K and N , therefore, 1F% RF% the anisotropy constants of rare-earth sublattice can be determined graphically using Eq. (3) by applying the sublattice magnetizations calculated by Eq. (2). The symbols shown in Fig. 1 are the magnetization curves of Dy Fe B single crystal measured 2 14 [12] along the [1 0 0], [1 1 0] and [0 0 1] directions at 4.2 K. Almost the same behavior along the [1 0 0] and [1 1 0] directions indicates, at least up to H"35 T, the negligible basal plane anisotropy or K &K +0. For the calculation of m and 3D: 5D: F% m using Eq. (2), the values for the anisotropy of D: Fe sublattice and the exchange interaction are needed, and K "115 J/kg [13—15] from 1F% Y Fe B experiments and N "0.827 T/ 2 14 D:F%
Y.B. Kim, H.-M. Jin / Journal of Magnetism and Magnetic Materials 189 (1998) 251—254
Fig. 1. Magnetization curves of Dy Fe B single crystal mea2 14 sured (symbols) [12] and calculated (solid lines) at 4.2 K along the [1 0 0], [1 1 0] and [0 0 1] directions.
253
Fig. 3. The plot ½ versus 4(m /M )3 to determine K . 2D: D: D: 2D:
Fig. 4. Magnetization curves of Tb Fe B single crystal mea2 14 sured (symbols) [5] and calculated (solid lines) at 4.2 K along the [1 0 0], [1 1 0] and [0 0 1] directions. Fig. 2. The plot ½
1D:
versus 2(m /M ) to determine K . D: D: 1D:
Am2 kg~1 [16] from high field free powder (HFFP) experiments are applied in analysis. Fig. 2 shows the plot ½ ("!M H#N 1D: D: D:F% M M M(m /M )!(m /M ) (J1!(m /M )2)/ F% D: F% F% D: D: F% F% (!J1!(m /M )2)N) versus 2(m /M ) to deterD: D: D: D: mine K . The curve at early stage shows linear 1D: relation, and K "1600 J/kg is obtained from 1D: the slope. The plot ½ ("2K (m /M )! 2D: 1D: D: D: M H#N M M M(m /M )!(m /M ) D: D:F% F% D: F% F% D: D: (J1!(m /M )2/(!J1!(m /M )2))N) versus F% F% D: D: 4(m /M )3 to determine K also has a linear D: D: 2D: relation, as shown in Fig. 3. All the experimental
data except H*25 T are on the line, and K "6600 J/kg is obtained from the line slope. 2D: The deviation of high field data from the line seems due to the improper value of exchange interaction. The magnetizations along the [1 0 0], [1 1 0] and [0 0 1] directions calculated by energy minimum method by applying the constants K " 1D: 1600 J/kg and K "6600 J/kg coincide with the 2D: experiments, as shown in Fig. 1 by solid lines. In addition, the sublattice moments are calculated to rotate on the plane made by the [0 0 1] axis and H as was assumed initially. The symbols in Fig. 4 show the magnetization curves of Tb Fe B [5] single crystal measured at 2 14
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Y.B. Kim, H.-M. Jin / Journal of Magnetism and Magnetic Materials 189 (1998) 251—254
1600 J/kg, K "6600 J/kg and K "4300 J/kg, 2D: 1T" respectively, when N "0.827 T/Am2 kg~1 and D:F% N "1.19 T/Am2 kg~1 is applied in analysis. T"F% References
Fig. 5. The plot ½ versus 2(m /M ) to determine K . 1T" T" T" 1T"
4.2 K. The compound also shows the nearly same magnetization behavior along the [1 0 0] and [1 1 0] directions, as shown in the figure. The plot ½ versus 2(m /M ) shows linear relation in1T" T" T" cluding all the experimental data measured up to H"18 T (See Fig. 5), and K "4300 J/kg is ob1T" tained from the slope. The magnetizations calculated by energy minimum method also coincide with the experiments, as shown by solid lines in Fig. 4. The calculation also showed the sublattice moments to rotate on the plane made by H and [0 0 1] axis. The magnetic parameters applied to analyze the anisotropy constants, and the analysis results are summarized in Table 1.
3. Conclusions The sublattice anisotropy constants of Dy Fe B 2 14 and Tb Fe B at 4.2 K are determined as K " 2 14 1D:
[1] J.J. Croat, J.F. Herbst, R.W. Lee, F.E. Pinkerton, J. Appl. Phys. 55 (1984) 2078. [2] M. Sagawa, S. Fujimura, N. Togawa, H. Yamamoto, Y. Matsuura, J. Appl. Phys. 55 (1984) 2083. [3] D. Givord, H.S. Li, R. Perrier de la Bathie, Solid State Commun. 51 (1984) 857. [4] M. Sagawa, J. Magn. Soc. Japan 9 (1985) 25. [5] D. Givord, H.S. Li, J.M. Cadogan, J.M.D. Coey, J.P. Gavigan, O. Yamada, H. Maruyama, M. Sagawa, S. Hirosawa, J. Appl. Phys. 63 (1988) 3713. [6] M. Yamada, H. Kato, H. Yamamoto, Y. Nakagawa, Phys. Rev. B 38 (1988) 620. [7] Zhu Yong, Zhao Tiesong, Jin Hanmin, Yang Fuming, Xie Jinqiang, Li Xinwen, Zhao Ruwen, F.R. de Boer, IEEE Trans. Magn. 25 (1989) 3443. [8] Y.B. Kim, Jin Han-min, J. Magn. Magn. Mater. 182 (1998) 55. [9] Y.B. Kim, Jin Han-min, J. Magnetics, 1998, submitted. [10] J.F. Herbst, J.J. Croat, F.E. Pinkerton, W.B. Yelon, Phys. Rev. B 29 (1984) 4176. [11] R. Verhoef, R.J. Radwanski, J.J.M. Franse, J. Magn. Magn. Mater. 89 (1990) 176. [12] Cited from; J.J.M. Franse, F.E. Kayzel, N.P. Thuy, J. Magn. Magn. Mater, 129 (1990) 26. [13] D. Givord, H.S. Li, R. Perrier de la Bathie, Solid State Commun. 51 (1984) 857. [14] H. Yamauchi, M. Yamada, Y. Yamaguchi, H. Yamamoto, S. Hirosawa, M. Sagawa, J. Magn. Magn. Mater. 54—57 (1986) 575. [15] K.H.J. Buschow, in: E.P. Wolfarth, K.H.J. Buschow (Eds.), Ferromagnetic Materials, North-Holland, Amsterdam, 1988, p. 21. [16] R. Verhoef, P.H. Quang, J.J.M. Franse, R.J. Radwanski, J. Magn. Magn. Mater. 83 (1990) 139.
Table 1 The magnetic parameters applied to analysis and the sublattice anisotropy constants of R Fe B (R"Dy, Tb) at 4.2 K 2 14 R Fe B 2 14 (R")
M ! R (Am2/kg)
M ! F% (Am2/kg)
N " RF% (T/Am2 kg~1)
K 1R (J/kg)
K 2R (J/kg)
Dy Tb
98.4 87.0
155.7 153.0
0.827 1.19
1600 4300
6600
!Calculated from saturation magnetization using the experimental Bohr magnetons [15] of rare-earth moments in R Fe B compound. 2 14 "Cited from Ref. [16].
Sublattice anisotropy constants of Dy Fe B and Tb Fe B 2 14 2 14 at 4.2 K Y.B. Kim*, Han-min Jin1 Korea Research Institute of Standards and Science, P.O. Box 3, Taedok Science Town, Taejon 305-600, South Korea Received 3 April 1998; received in revised form 19 May 1998
Abstract The rare-earth sublattice anisotropy of Dy Fe B and Tb Fe B at 4.2 K have been analyzed by semi-graphical 2 14 2 14 method on the bases of two sublattice model. The anisotropy constants of Dy-sublattice are determined as K " 1D: 1600 J/kg and K "6600 J/kg, and the constant of Tb-sublattice as K "4300 J/kg. The magnetizations calculated 2$: 1T" by energy minimum method by applying the sublattice anisotropy constants reproduced well the experiments and satisfied the simulation assumptions. ( 1998 Elsevier Science B.V. All rights reserved. PACS: 75.30.Gw; 75.70.Vv; 75.50.Ww Keywords: Magnetocrystalline anisotropy; Sublattice anisotropy; Rare-earth—3d transition metal compounds
1. Introduction NdFeB alloy [1,2] shows excellent hard magnetic properties and is widely used as the raw material for the high-coercive high-energy permanent magnets. The high coercivity is originated from the strong uniaxial magnetocrystalline anisotropy of Nd Fe B at room temperature [3]. 2 14
* Corresponding author. Fax: #82 42 868 5018; e-mail: [email protected]. 1 Guest scientist from Jilin University, Changchun, P.R. China. Supported by the Brain Pool Project of the Korean Federation of Science and Technology Societies.
Dy Fe B [4] and Tb Fe B [4] are known to 2 14 2 14 have much stronger anisotropy than Nd Fe B, 2 14 and Dy or Tb are added to increase the coercivity of NdFeB-type magnets. The magnetocrystalline anisotropy of Dy Fe B and Tb Fe B may be 2 14 2 14 understood to some extent from their crystalline electric field (CEF) parameters [5—7], because the anisotropy constants can be calculated [6] from the CEF parameters. The exact calculation, however, is only possible when the magnetic moments of rareearth and Fe sublattices are colinear which may occur near room temperature. At low temperature near 4.2 K, the sublattice moments are usually non-colinear due to the strong magnetocrystalline anisotropy of rare-earth sublattice, and the
0304-8853/98/$19.00 ( 1998 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 9 8 ) 0 0 2 1 5 - 7
252
Y.B. Kim, H.-M. Jin / Journal of Magnetism and Magnetic Materials 189 (1998) 251—254
anisotropy constants cannot be deduced from CEF parameters. Recently, the authors have suggested the graphical methods [8,9] to analyze the anisotropy of uniaxial magnetocrystalline anisotropy system. The methods are simple and give the anisotropy constants directly from magnetization curves of magnetization easy or hard direction within hard magnetization plane. Dy Fe B and Tb Fe B 2 14 2 14 show uniaxial magnetocrystalline anisotropy below their Curie temperatures. In this paper, we report the anisotropy constants of rare-earth sublattice of the compounds analyzed by the semigraphical method.
2. Analysis results The rare-earth elements in R Fe B-type 2 14 (R"rare-earth elements) compounds occupy crystallographically different f and g sites [10]. Though the rare-earth moments occupy the different sites, treating them as one sublattice resulted in a good approximation [9] in analyzing the anisotropy constants of rare-earth sublattice. Dy Fe B and Tb Fe B show the uniaxial 2 14 2 14 magnetocrystalline anisotropy with easy magnetization tetragonal c-axis at 4.2 K. If we assume the compounds as a two sublattice system of Fe and rare-earth moment, and every moments to rotate on the plane made by H and c-axis [8,9], the free energy of the system in a magnetic field parallel to [1 0 0] or [1 1 0] direction is expressed as follows: E"K sin2 h #K sin2 h 1F% F% 1R R #(K $K )sin4 h #(K $K )sin6 h 2 2R 3R R 4R 5R R !M H sin h !M H sin h F% F% R R #N M M (sin h sin h RF% F% R F% R #cos h cos h ). (1) F% R Here, the notation h implies the inclination angle of sublattice moments from the [0 0 1] axis. The anisotropy of Fe-sublattice is assumed to have the first order only and the constant is expressed as K . K (i"1,2,2,) is the ith anisotropy con1F% iR stant of rare-earth sublattice. M and M are the F% R
magnetizations of Fe and rare-earth sublattice, respectively. N is the macroscopic exchange RF% interaction coefficient between rare-earth and Fe sublattices, which is well defined in Ref. [11], and is treated in Eq. (1) as positive for antiferromagnetic coupling. The $ sign of K and K becomes 3R 5R positive when H is parallel to [1 0 0] and negative when H is parallel to [1 1 0]. If we define the magnetizations observed in field direction as m and the contribution of Fe and rare-earth sublattice as m and m , respectively, we F% R can obtain the following relations from the equilibrium condition of free energy.
G
m!m m m!m R!M H#N M M R! R 2K 1F% M F% RF% F% R M M F% R F%
H
!J1!(m /M )2 R R "0, J1!(m!m )2/M2 F% R
(2)
A B A B
m 3 m R #4 R (K $K ) 2K 2R 3R 1RM M R R #6
m 5 R (K $K )!M H 4R 5R R M R
G
m F% #N M M RF% F% R M F%
H
m J1!(m /M )2 F% F% ! R "0. M !J1!(m /M )2 R R R
(3)
If we know the values of K and N , therefore, 1F% RF% the anisotropy constants of rare-earth sublattice can be determined graphically using Eq. (3) by applying the sublattice magnetizations calculated by Eq. (2). The symbols shown in Fig. 1 are the magnetization curves of Dy Fe B single crystal measured 2 14 [12] along the [1 0 0], [1 1 0] and [0 0 1] directions at 4.2 K. Almost the same behavior along the [1 0 0] and [1 1 0] directions indicates, at least up to H"35 T, the negligible basal plane anisotropy or K &K +0. For the calculation of m and 3D: 5D: F% m using Eq. (2), the values for the anisotropy of D: Fe sublattice and the exchange interaction are needed, and K "115 J/kg [13—15] from 1F% Y Fe B experiments and N "0.827 T/ 2 14 D:F%
Y.B. Kim, H.-M. Jin / Journal of Magnetism and Magnetic Materials 189 (1998) 251—254
Fig. 1. Magnetization curves of Dy Fe B single crystal mea2 14 sured (symbols) [12] and calculated (solid lines) at 4.2 K along the [1 0 0], [1 1 0] and [0 0 1] directions.
253
Fig. 3. The plot ½ versus 4(m /M )3 to determine K . 2D: D: D: 2D:
Fig. 4. Magnetization curves of Tb Fe B single crystal mea2 14 sured (symbols) [5] and calculated (solid lines) at 4.2 K along the [1 0 0], [1 1 0] and [0 0 1] directions. Fig. 2. The plot ½
1D:
versus 2(m /M ) to determine K . D: D: 1D:
Am2 kg~1 [16] from high field free powder (HFFP) experiments are applied in analysis. Fig. 2 shows the plot ½ ("!M H#N 1D: D: D:F% M M M(m /M )!(m /M ) (J1!(m /M )2)/ F% D: F% F% D: D: F% F% (!J1!(m /M )2)N) versus 2(m /M ) to deterD: D: D: D: mine K . The curve at early stage shows linear 1D: relation, and K "1600 J/kg is obtained from 1D: the slope. The plot ½ ("2K (m /M )! 2D: 1D: D: D: M H#N M M M(m /M )!(m /M ) D: D:F% F% D: F% F% D: D: (J1!(m /M )2/(!J1!(m /M )2))N) versus F% F% D: D: 4(m /M )3 to determine K also has a linear D: D: 2D: relation, as shown in Fig. 3. All the experimental
data except H*25 T are on the line, and K "6600 J/kg is obtained from the line slope. 2D: The deviation of high field data from the line seems due to the improper value of exchange interaction. The magnetizations along the [1 0 0], [1 1 0] and [0 0 1] directions calculated by energy minimum method by applying the constants K " 1D: 1600 J/kg and K "6600 J/kg coincide with the 2D: experiments, as shown in Fig. 1 by solid lines. In addition, the sublattice moments are calculated to rotate on the plane made by the [0 0 1] axis and H as was assumed initially. The symbols in Fig. 4 show the magnetization curves of Tb Fe B [5] single crystal measured at 2 14
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Y.B. Kim, H.-M. Jin / Journal of Magnetism and Magnetic Materials 189 (1998) 251—254
1600 J/kg, K "6600 J/kg and K "4300 J/kg, 2D: 1T" respectively, when N "0.827 T/Am2 kg~1 and D:F% N "1.19 T/Am2 kg~1 is applied in analysis. T"F% References
Fig. 5. The plot ½ versus 2(m /M ) to determine K . 1T" T" T" 1T"
4.2 K. The compound also shows the nearly same magnetization behavior along the [1 0 0] and [1 1 0] directions, as shown in the figure. The plot ½ versus 2(m /M ) shows linear relation in1T" T" T" cluding all the experimental data measured up to H"18 T (See Fig. 5), and K "4300 J/kg is ob1T" tained from the slope. The magnetizations calculated by energy minimum method also coincide with the experiments, as shown by solid lines in Fig. 4. The calculation also showed the sublattice moments to rotate on the plane made by H and [0 0 1] axis. The magnetic parameters applied to analyze the anisotropy constants, and the analysis results are summarized in Table 1.
3. Conclusions The sublattice anisotropy constants of Dy Fe B 2 14 and Tb Fe B at 4.2 K are determined as K " 2 14 1D:
[1] J.J. Croat, J.F. Herbst, R.W. Lee, F.E. Pinkerton, J. Appl. Phys. 55 (1984) 2078. [2] M. Sagawa, S. Fujimura, N. Togawa, H. Yamamoto, Y. Matsuura, J. Appl. Phys. 55 (1984) 2083. [3] D. Givord, H.S. Li, R. Perrier de la Bathie, Solid State Commun. 51 (1984) 857. [4] M. Sagawa, J. Magn. Soc. Japan 9 (1985) 25. [5] D. Givord, H.S. Li, J.M. Cadogan, J.M.D. Coey, J.P. Gavigan, O. Yamada, H. Maruyama, M. Sagawa, S. Hirosawa, J. Appl. Phys. 63 (1988) 3713. [6] M. Yamada, H. Kato, H. Yamamoto, Y. Nakagawa, Phys. Rev. B 38 (1988) 620. [7] Zhu Yong, Zhao Tiesong, Jin Hanmin, Yang Fuming, Xie Jinqiang, Li Xinwen, Zhao Ruwen, F.R. de Boer, IEEE Trans. Magn. 25 (1989) 3443. [8] Y.B. Kim, Jin Han-min, J. Magn. Magn. Mater. 182 (1998) 55. [9] Y.B. Kim, Jin Han-min, J. Magnetics, 1998, submitted. [10] J.F. Herbst, J.J. Croat, F.E. Pinkerton, W.B. Yelon, Phys. Rev. B 29 (1984) 4176. [11] R. Verhoef, R.J. Radwanski, J.J.M. Franse, J. Magn. Magn. Mater. 89 (1990) 176. [12] Cited from; J.J.M. Franse, F.E. Kayzel, N.P. Thuy, J. Magn. Magn. Mater, 129 (1990) 26. [13] D. Givord, H.S. Li, R. Perrier de la Bathie, Solid State Commun. 51 (1984) 857. [14] H. Yamauchi, M. Yamada, Y. Yamaguchi, H. Yamamoto, S. Hirosawa, M. Sagawa, J. Magn. Magn. Mater. 54—57 (1986) 575. [15] K.H.J. Buschow, in: E.P. Wolfarth, K.H.J. Buschow (Eds.), Ferromagnetic Materials, North-Holland, Amsterdam, 1988, p. 21. [16] R. Verhoef, P.H. Quang, J.J.M. Franse, R.J. Radwanski, J. Magn. Magn. Mater. 83 (1990) 139.
Table 1 The magnetic parameters applied to analysis and the sublattice anisotropy constants of R Fe B (R"Dy, Tb) at 4.2 K 2 14 R Fe B 2 14 (R")
M ! R (Am2/kg)
M ! F% (Am2/kg)
N " RF% (T/Am2 kg~1)
K 1R (J/kg)
K 2R (J/kg)
Dy Tb
98.4 87.0
155.7 153.0
0.827 1.19
1600 4300
6600
!Calculated from saturation magnetization using the experimental Bohr magnetons [15] of rare-earth moments in R Fe B compound. 2 14 "Cited from Ref. [16].