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Hard magnetic properties of Sm3Fe26.7VxN4 and Sm3Fe26.7VxCy
Journal of Magnetism and Magnetic Materials 192 (1999) 314 —320
Hard magnetic properties of Sm Fe VN V and Sm Fe VC V W Xiu-Feng Han *, M.C. Zhang, Yi Qiao, F.M. Yang, C.P. Yang, G.C. Liu, Y.Z. Wang, B.P. Hu Material Science Center, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, People’s Republic of China State Key Laboratory for Magnetism, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100080, People’s Republic of China State Key Laboratory for Advanced Materials, University of Sciences and Technology Beijing, Beijing 100083, People’s Republic of China San Huan Research Laboratory, Chinese Academy of Sciences, P.O. Box 603, Beijing 100080, People’s Republic of China Received 19 February 1998; received in revised form 5 November 1998
Abstract Sm Fe V N nitrides and Sm Fe V C carbides have been synthesized by gas—solid phase reaction. Their W hard magnetic properties have been investigated by means of additional ball-milling at room temperature. The saturation magnetization of Sm Fe V N almost decreases linearly with increasing ball-milling time t, but that of Sm Fe V C has no obvious change when the ball-milling time increases from t"1 to 28 h. As a preliminary result, W the maximum remanence B of 0.94 and 0.88 T, the coercivity k H of 0.75 and 0.25 T, and the maximum energy product G ! (BH) of 108.5 and 39.1 kJ/m for their resin-bonded permanent magnets are achieved, respectively, by ball-milling at 293 K. 1999 Published by Elsevier Science B.V. All rights reserved. PACS: 75.50.Bb; 75.50.Ww; 75.60.Zj; 75.30.Cr; 75.30.Gw Keywords: Hard magnetic properties; Coercivity; Remanence; Magnetic energy product
1. Introduction Nd Fe B [1], Sm Fe carbides [2] and ni trides [3], and Nd(Fe,Ti) nitrides [4] show
* Correspondence address: Department of Applied Physics, Graduate School of Engineering, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan. Fax: #81-22-217799-9; e-mail: [email protected].
excellent intrinsic hard magnetic properties in the rare-earth—iron intermetallic compounds. Following those works, recently much attention has been paid to the novel rich-iron intermetallic compounds R (Fe,T) (R"rare earth, T"transition metal) and their nitrides and carbides [5—20]. Among them, the Sm (Fe,Ti) N nitride, with W a strong uniaxial anisotropy, high magnetic ordering temperature (750 K), high saturation magnetization (1.3 T) and large anisotropy field
0304-8853/99/$ — see front matter 1999 Published by Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 9 8 ) 0 0 5 3 8 - 1
X.-F. Han et al. / Journal of Magnetism and Magnetic Materials 192 (1999) 314 —320
(13 T), was considered as a new potential candidate for hard magnet application [11,12]. A coercivity of k H "0.83 T in Sm (Fe,Ti) N at room temperG ! W ature (RT) has been achieved [11]. The Sm (Fe,Ti) C carbide also can be probably used W as raw material for permanent magnet due to its good hard magnetic properties [13]. One can therefore believe that the nitrides and carbides of Sm (Fe,T) (T"V, Cr, and Mo) will also have good hard magnetic properties. The hard magnetic properties of coarse powder of Sm (Fe,Cr) N with variation in N concentration W at RT were reported by Suzuki et al. [21]. A comparison of the enhancement of coercivity H by ( ! means of additional milling and Zn-bonding for Sm (Fe Ti ) X (X"N and C) was given by W Mu¨ller et al. [22]. The influence of interstitial H and N on the structural and basic magnetic properties of Sm (Fe,T) (T"Ti, V, and Cr) at 4.2 K and RT was carefully clarified by Koyama et al. [23]. A series of R (Fe,T) (R"Y, Ce, Nd, Sm, Gd, Tb, and Dy; T"V, Cr, and Mo) compounds and their nitrides have been systematically synthesized [24—27], and the hard magnetic properties of the Sm (Fe,Cr) N nitrides and Sm (Fe,Cr) C W W carbides have been specially described in our previous papers [28,29]. In this work, the hard magnetic properties of the interstitial nitride Sm (Fe,V) N and carbide Sm (Fe,V) C have been investigated. The max W imum values of remanence B , the coercivity k H , G ! and the energy product (BH) of their resin-bonded permanent magnets are achieved by means of additional ball-milling at 293 K.
2. Experimental methods In order to prepare nitrides and carbides, the samples of Sm Fe V were pulverized into fine powder with an average particle size of about 15 lm. The gas-phase reaction between the alloy powder and nitrogen or acetylene was performed by heating the fine powder in nitrogen or acetylene gas at an ambient pressure and at temperatures ranging from 803 to 823 K for about 3 h. In order to avoid the hydrogen being absorbed into the sample, the sample space was pumped before cool-
315
ing in carbonation. The X-ray diffraction (XRD) patterns and thermo-magnetic analysis (TMA) showed that all samples of Sm (Fe,V) N and Sm (Fe,V) C were good phased and crystal W lized in the Nd (Fe,Ti) -type structure as that of the parent compounds, except for an estimated amount of a-Fe inside. Magnetic balance method (MBM) in a field of 1.2 T on the loose powder was used to examining the amount of the impurity phase a-Fe in nitrided and carbonated powder samples. The thermo-magnetic curve M(¹) for each free powder sample of Sm (Fe,V) and its nitride and carbide was, respectively, measured with a vibrating-sample magnetometer (VSM) in a low field of 0.04 T from 1.5 K to above Curie temperature. The Curie temperature ¹ was determined from M—¹ ! plot, which was derived from M(¹), by extrapolating M to zero. The Curie temperature ¹ of ! Sm (Fe,V) N and Sm (Fe,V) C , respectively, W increased about 181 and 189 K comparing with the parent compound. The N concentration in the Sm Fe V N compounds was obtained from \V V W the mass difference before and after nitrogenation. The anisotropy direction was deduced from the XRD patterns of finely ground powder samples mixed with epoxy which were oriented in a magnetic field of about 1.2 T. The nitride and carbide powders were then ballmilled in petroleum ether using metal balls of 4—10 mm diameter with a sample-to-metal-ball weight ratio of 1 to 60. The magnetically aligned cylinder samples that were to be exposed to ballmilling, for various times t, were made by mixing the powders with about 50% epoxy resin, and then solidifying them in an applied field of about 1.2 T. The hysteresis loops of each sample were measured using a VSM at RT. The demagnetization factor was corrected according to the shape and size for each sample.
3. Results and discussion After nitrogenation the easy magnetization direction (EMD) of Sm Fe V changed into the b-axis from the easy-cone structure. Only Sm Fe V N shows the uniaxial anisotropy
316
X.-F. Han et al. / Journal of Magnetism and Magnetic Materials 192 (1999) 314 —320
Table 1 The monoclinic lattice parameters, a, b, c, and b, and the unit cell volume »"abc sin b used in the analysis of X-ray data with the A2/m space group, the X-ray density o estimated based on the lattice constants, and the expansion d»/» of the unit-cell volume upon nitrogenation and carbonation for Sm Fe V compounds Sm Fe V (N,C) \V V W
a (nm)
b (nm)
c (nm)
b (deg.)
» (nm)
o (g/cm)
d»/» (%)
Sm Fe V Sm Fe V N Sm Fe V C W
1.061 1.084 1.083
0.855 0.869 0.870
0.971 0.989 0.985
96.86 97.05 97.39
0.874 0.924 0.920
7.83 7.60 7.6
5.8 5.4
and other nitrides in the series of R Fe VN \V V (R"Y, Ce, Nd, Gd, Tb, and Dy) compounds display the easy-plane anisotropy. The quantitative analysis of the exchange and crystal-field interactions in R (Fe,Ti) and R (Fe,Ti) N (R"Nd W and Sm) showed that Sm (Fe,Ti) N nitride be W come uniaxial anisotropic for y*2 [30], which also compared well with our experimental results. Like Sm Fe V N , the Sm Fe V C com W pounds also shows the uniaxial anisotropy. Table 1 gives the crystallographic parameters, the unit cell volume », the X-ray density o estimated based on the lattice constants, and the expansion d»/» of the unit-cell volume upon nitrogenation and carbonation for Sm Fe V compounds investigated here. After nitrogenation and carbonation the relative volume expansion is about 5.8 and 5.4%. For examining the amount of the impurity phase a-Fe in powder samples, the magnetization as a function of temperature are measured with a MBM in a field of 1.2 T on the loose powder samples of Sm Fe V N and Sm Fe V C W in the temperature range from RT to above 900 K as shown in Fig. 1, where the loose powder samples are free to be reoriented in the applied magnetic field. It is shown that in contribution to the magnetization the main impurity phase in nitride and carbide powder samples comes from a-Fe, and other impurity phases can be neglected. It is well known that the saturation magnetization of pure iron, BCC-Fe, at RT and 4.2 K are 217.2 and 221.7 Am/kg, respectively, and the values of saturation magnetization of the pure iron can be roughly thought to change linearly with decreasing temperature from RT to 4.2 K. So the saturation
Fig. 1. Thermomagnetic curves for Sm Fe V N and Sm Fe V C in a field of 1.2 T. W
magnetization contributed by the impurity phase a-Fe at RT and 4.2 K can be approximately derived from M—¹ plots by extrapolating M from the high temperature (700—900 K) to RT and then to 4.2 K. As an example, the concentration of impurity phase a-Fe in the nitride powder sample of Sm Fe V N is approximately determined to be 9.7 wt%, derived from (21.1 Am/kg)/ (217.2 Am/kg). The value of 21.1 Am/kg is the saturation magnetization at RT contributed by the impurity phase a-Fe in the nitride powder sample, derived from M—¹ plots by linearly extrapolating M from the high temperature (700—900 K) to RT, whereas the saturation magnetization at 4.2 K contributed by the impurity phase a-Fe in the nitride powder sample can be obtained by (21.1 Am/kg)* (221.7 Am/kg)/(217.2 Am/kg)"21.5 Am/kg.
X.-F. Han et al. / Journal of Magnetism and Magnetic Materials 192 (1999) 314 —320
The concentration of the impurity phase a-Fe in the carbide powder sample of Sm Fe V C is W approximately examined as 15.3 wt%. The saturation magnetization M and anisot1 ropy field H are measured by means of a VSM with applied field strengths of up to 7 T at 4.2 K, and by a pulsed magnetic field (PMF) up to 10 T at RT for the magnetically aligned samples of Sm Fe V N and Sm Fe V C . The ac W tual saturation magnetization at 4.2 K and RT can be obtained after deducting the contribution of the impurity phase a-Fe in the samples. As an example, before and after deducting the contribution of the impurity phase a-Fe the saturation magnetization of Sm Fe V N at RT are 143.6 and 135.7 Am/kg, which derived from (143.6—21.1) Am/ (1—0.097) kg"135.7 Am/kg. The good intrinsic magnetic properties of Sm Fe V N (¹ "683 K, M (RT)"135.7 ! 1 Am/kg, and k H (RT)"6.7 T) and Sm Fe V C (¹ "691 K, M (RT)" 97.5 Am/kg) make W ! 1 us believe that the nitrides and carbides of Sm Fe V have good hard magnetic properties. \V V Fig. 2 shows the variation of hard magnetic properties of Sm Fe V N powder with ball milling time t. As the ball-milling time t increases, the saturation magnetization M of Sm Fe V N 1 almost decreases linearly. The value of M de1 creases to near 70% of the value for the non-milled powder when t"28 h as shown in Fig. 2a. The reason is that, by ball milling, the grains are broken and the crystalline structure in the surface of the particles is destroyed, so the main phase of Sm Fe V N decreases while the non-mag netic impurity appears. This was observed in the XRD patterns with different ball-milling time. The longer the ball-milling time t is, the worse the XRD pattern does. The remanence B of Sm Fe V N powder increases quickly at the initial stage of the ball milling, appears to have a plateau for milling times between t"1 and 12 h and reaches a maximum value of 0.94 T at 12 h, and then decreases slowly. The coercivity k H has a different feature G ! from the remanence. With increasing ball-milling time t, k H increases almost linearly until G ! t"24 h, reaches a plateau of about 0.75 T between t"24 and 32 h, and then decreases slowly. The energy product (BH) increases gradually from
317
Fig. 2. The variation of hard magnetic properties of Sm Fe V N powder with ball-milling time t at 293 K.
a small value at the beginning of the ball milling to a maximum value of 108.5 kJ/m when t"12 h, and then decreases slowly. Obviously, (BH) is
influenced by the coercivity, the remanence, and the shape of the demagnetization curve. A good resin-bonded magnet with a remanence B of 0.94 T, a coercivity k H of 0.53 T and an G ! energy product (BH) of 108.5 kJ/m was ob tained using the Sm Fe V N powder after ball-milling 12 h at 293 K.
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X.-F. Han et al. / Journal of Magnetism and Magnetic Materials 192 (1999) 314 —320
Fig. 4. The typical hysteresis loops of Sm Fe V C powder W with a ball-milling time 6 and 24 h at 293 K.
Fig. 3. The variation of hard magnetic properties of Sm Fe V C powder with ball-milling time t at 293 K. W
Fig. 3 illustrates the variation of hard magnetic properties of Sm Fe V C powder with ball W milling time t. As the ball-milling time t increases, the saturation magnetization M of Sm Fe V C 1 W has no obvious change until t"28 h as shown in Fig. 3a. The remanence B of Sm Fe V C W powder also increases rapidly at the beginning of the ball milling, reaches a maximum value of 0.88 T at 6 h and then decreases slowly. The coercivity k H increases gradually from a small value at the G ! initial stage of the ball milling to a maximum value
of 0.25 T when t"24 h, and then decreases slowly. The energy product (BH) increases rapidly from
a small value at the beginning of the ball milling to a maximum value of 39.1 kJ/m when t"6 h, and then decreases slowly. As an example, Fig. 4 shows the typical hysteresis loops of Sm Fe V C W measured with a VSM at 293 K when ball-milling 6 and 24 h. A good resin-bonded magnet with a remanence B of 0.81 T, a coercivity k H of 0.25 T, and an G ! energy product (BH) of 37.0 kJ/m was obtained
using the Sm Fe V C powder after ball-mill W ing 24 h at 293 K. Table 2 gives the Curie temperature ¹ , the max! imum values of remanence B , the coercivity k H , G ! and the energy product (BH) for the nitride magnet Sm Fe V N and the carbide magnet Sm Fe V C . The hard magnetic parameters W for other associated nitride and carbide magnets of Sm Fe T (T"Ti [11—13] and Cr [21,28,29]) \V V are also listed in the table for reference.
4. Conclusions The good intrinsic magnetic properties of Sm Fe V N (¹ "683 K, M (RT)"135.7 ! 1 Am/kg, and k H (RT)"6.7 T) and Sm Fe V C (¹ "691 K, M (RT)"97.5 Am/kg) make W ! 1
X.-F. Han et al. / Journal of Magnetism and Magnetic Materials 192 (1999) 314 —320
319
Table 2 The Curie temperature ¹ , the maximum values of remanence B , the coercivity k H , and the energy product (BH) for the nitride and ! G ! carbide magnets of Sm Fe V and other associated nitride and carbide magnets of Sm Fe T (T"Ti and Cr) \V V Magnets
¹ ! (K)
B (RT) (T)
k H (RT) G ! (T)
(BH) (RT)
(kJ/m)
Refs.
Sm Fe V N Sm Fe V C W Sm Fe Ti N W Sm Fe Ti C W Sm Fe Cr N W Sm Fe Cr N W Sm Fe Cr C W
683 691 750 641
0.94 0.88 1.04
0.75 0.25 0.83 0.3 0.65 0.79 0.80
108.5 39.1 105
This work This work [11,12] [13] [21] [28] [29]
686 559
0.84 0.86 0.80
these compounds the hopeful candidates for new high-performance permanent magnets. As a preliminary result for the resin-bonded permanent magnets of Sm Fe V N and Sm Fe V C , W the maximum values of remanence B of 0.94 and 0.88 T, the coercivity k H of 0.75 and 0.25 T, and G ! the energy product (BH) of 108.5 and 39.1 kJ/m are achieved by means of additional ball-milling at 293 K, respectively. The hard magnetic properties of Sm Fe V N at RT is better than that of Sm Fe V C in the present research results. W Acknowledgements Project supported by the State Committee of Science and Technology and the National Natural Science Foundation of China, and in part by National Key Laboratory of Theoretical Computational Chemistry, Jilin University.
[6] [7] [8] [9] [10]
[11]
[12]
[13]
[14]
References [1] M. Sagawa, S. Fujimura, M. Togawa, Y. Matuura, J. Appl. Phys. 55 (1984) 2083. [2] X.P. Zhong, R.J. Radwanski, F.R. de Boer, T.H. Jacobs, K.H.J. Buschow, J. Magn. Magn. Mater. 86 (1990) 333. [3] J.M.D. Coey, H. Sun, J. Magn. Magn. Mater. 87 (1990) L251. [4] Y.C. Yang, X.D. Zhang, L.S. Kong, Q. Pan, S.L. Ge, Proc. 11th Int. Workshop on Rare-Earth Magnets and their Application, Vol. 2, 1990, p. 190. [5] S.J. Collocott, R.K. Day, J.B. Dunlop, R.L. Davis, Proc. 7th Int. Symp. on Magnetic Anisotropy and Coercivity in
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Rare-Earth—Transition Metal Alloys, Canberra, 1992, Hi-Perm Laboratory, Research Center for Advanced Mineral and Material Processing, University of Western Australia, p. 437. H.S. Li, J.M. Cadogan, R.L. Davis, A. Margarian, J.B. Dunlop, Solid State Commun. 90 (1994) 487. C.D. Fuerst, F.E. Pinkerton, J.F. Herbst, J. Appl. Phys. 76 (1994) 6144. D.H. Ryan, J.M. Cadogan, A. Margarian, J.B. Dunlop, J. Appl. Phys. 76 (1994) 6150. A. Margarian, J.B. Dunlop, R.K. Day, W. Kalceff, J. Appl. Phys. 76 (1994) 6153. J.M. Cadogan, H.S. Li, A. Margarian, J.B. Dunlop, D.H. Ryan, S.J. Collocott, R.L. Davis, J. Appl. Phys. 76 (1994) 6138. F.M. Yang, B. Nasunjilegal, J.L. Wang, J.J. Zhu, W.D. Qin, N. Tang, R.W. Zhao, B.P. Hu, Y.Z. Wang, H.S. Li, J. Phys.: Condens. Matter 7 (1995) 1679. B.P. Hu, G.C. Liu, Y.Z. Wang, B. Nasunjilegal, R.W. Zhao, F.M. Yang, H.S. Li, J.M. Cadogan, J. Phys.: Condens. Matter 6 (1994) L197. B.P. Hu, G.C. Liu, Y.Z. Wang, B. Nasunjilegal, N. Tang, F.M. Yang, H.S. Li, J.M. Cadogan, J. Phys.: Condens. Matter 6 (1994) L595. L. Morellon, P.A. Algarabel, M.R. Ibarra, J. Kamara´d, Z. Arnold, L. Pareti, F. Albertini, A. Paoluzi, J. Magn. Magn. Mater. 150 (1994) L285. M.R. Ibarra, L. Morellon, J. Blasco, L. Pareti, P.A. Algarabel, J. Garcı` a, F. Albertini, A. Paoluzi, J. Phys.: Condens. Matter 6 (1994) L717. C.D. Fuerst, P.E. Pinkerton, J.F. Herbst, J. Magn. Magn. Mater. 129 (1994) L115. O. Kalogirou, V. Psycharis, L. Saettas, D.N. Niarchos, J. Magn. Magn. Mater. 146 (1995) 335. W.B. Yelon, Z. Hu, J. Appl. Phys. 79 (1996) 1330. Z. Hu, W.B. Yelon, O. Kalogirou, V. Psycharis, J. Appl. Phys. 80 (1996) 2955. Ye V. Shcherbakova, G.V. Ivanova, M.I. Bartashevich, V.I. Khrabrov, Ye V. Belozerov, J. Alloys Compounds 240 (1996) 101.
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[21] S. Suzuki, S. Suzuki, M.K. Awasaki, IEEE Trans. Magn. 31 (1995) 3695. [22] K.H. Mu¨ller, J.B. Dunlop, A. Handstein, B. Gebel, P.A.P. Wendhausen, J. Magn. Magn. Mater. 157/158 (1996) 117. [23] K. Koyama, H. Fujii, S. Suzuki, J. Magn. Magn. Mater. 161 (1996) 118. [24] X.F. Han, F.M. Yang, H.G. Pan, Y.G. Wang, J.L. Wang, H.L. Liu, N. Tang, R.W. Zhao, H.S. Li, J. Appl. Phys. 81 (1997) 7450. [25] X.F. Han, F.M. Yang, Q.S. Li, M.C. Zhang, S.Z. Zhou, J. Phys.: Condens. Matter 10 (1998) 151.
[26] X.F. Han, F.M. Yang, H.G. Pan, Y.G. Wang, Y.Z. Wang, J. Appl. Phys. 83 (1998) 4366. [27] H.G. Pan, F.M. Yang, Y. Chen, X.F. Han, N. Tang, C.P. Chen, Q.D. Wang, J. Phys.: Condens. Matter 9 (1997) 2499. [28] Y.Z. Wang, B.P. Hu, G.C. Liu, H.S. Li, X.F. Han, C.P. Yang, J. Phys.: Condens. Matter 9 (1997) 2787. [29] Y.Z. Wang, B.P. Hu, G.C. Liu, H.S. Li, X.F. Han, C.P. Yang, J. Phys.: Condens. Matter 9 (1997) 2793. [30] H.S. Li, D. Courtois, J.M. Cadogan, J. Appl. Phys. 79 (1996) 4622.
Hard magnetic properties of Sm Fe VN V and Sm Fe VC V W Xiu-Feng Han *, M.C. Zhang, Yi Qiao, F.M. Yang, C.P. Yang, G.C. Liu, Y.Z. Wang, B.P. Hu Material Science Center, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, People’s Republic of China State Key Laboratory for Magnetism, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100080, People’s Republic of China State Key Laboratory for Advanced Materials, University of Sciences and Technology Beijing, Beijing 100083, People’s Republic of China San Huan Research Laboratory, Chinese Academy of Sciences, P.O. Box 603, Beijing 100080, People’s Republic of China Received 19 February 1998; received in revised form 5 November 1998
Abstract Sm Fe V N nitrides and Sm Fe V C carbides have been synthesized by gas—solid phase reaction. Their W hard magnetic properties have been investigated by means of additional ball-milling at room temperature. The saturation magnetization of Sm Fe V N almost decreases linearly with increasing ball-milling time t, but that of Sm Fe V C has no obvious change when the ball-milling time increases from t"1 to 28 h. As a preliminary result, W the maximum remanence B of 0.94 and 0.88 T, the coercivity k H of 0.75 and 0.25 T, and the maximum energy product G ! (BH) of 108.5 and 39.1 kJ/m for their resin-bonded permanent magnets are achieved, respectively, by ball-milling at 293 K. 1999 Published by Elsevier Science B.V. All rights reserved. PACS: 75.50.Bb; 75.50.Ww; 75.60.Zj; 75.30.Cr; 75.30.Gw Keywords: Hard magnetic properties; Coercivity; Remanence; Magnetic energy product
1. Introduction Nd Fe B [1], Sm Fe carbides [2] and ni trides [3], and Nd(Fe,Ti) nitrides [4] show
* Correspondence address: Department of Applied Physics, Graduate School of Engineering, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan. Fax: #81-22-217799-9; e-mail: [email protected].
excellent intrinsic hard magnetic properties in the rare-earth—iron intermetallic compounds. Following those works, recently much attention has been paid to the novel rich-iron intermetallic compounds R (Fe,T) (R"rare earth, T"transition metal) and their nitrides and carbides [5—20]. Among them, the Sm (Fe,Ti) N nitride, with W a strong uniaxial anisotropy, high magnetic ordering temperature (750 K), high saturation magnetization (1.3 T) and large anisotropy field
0304-8853/99/$ — see front matter 1999 Published by Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 9 8 ) 0 0 5 3 8 - 1
X.-F. Han et al. / Journal of Magnetism and Magnetic Materials 192 (1999) 314 —320
(13 T), was considered as a new potential candidate for hard magnet application [11,12]. A coercivity of k H "0.83 T in Sm (Fe,Ti) N at room temperG ! W ature (RT) has been achieved [11]. The Sm (Fe,Ti) C carbide also can be probably used W as raw material for permanent magnet due to its good hard magnetic properties [13]. One can therefore believe that the nitrides and carbides of Sm (Fe,T) (T"V, Cr, and Mo) will also have good hard magnetic properties. The hard magnetic properties of coarse powder of Sm (Fe,Cr) N with variation in N concentration W at RT were reported by Suzuki et al. [21]. A comparison of the enhancement of coercivity H by ( ! means of additional milling and Zn-bonding for Sm (Fe Ti ) X (X"N and C) was given by W Mu¨ller et al. [22]. The influence of interstitial H and N on the structural and basic magnetic properties of Sm (Fe,T) (T"Ti, V, and Cr) at 4.2 K and RT was carefully clarified by Koyama et al. [23]. A series of R (Fe,T) (R"Y, Ce, Nd, Sm, Gd, Tb, and Dy; T"V, Cr, and Mo) compounds and their nitrides have been systematically synthesized [24—27], and the hard magnetic properties of the Sm (Fe,Cr) N nitrides and Sm (Fe,Cr) C W W carbides have been specially described in our previous papers [28,29]. In this work, the hard magnetic properties of the interstitial nitride Sm (Fe,V) N and carbide Sm (Fe,V) C have been investigated. The max W imum values of remanence B , the coercivity k H , G ! and the energy product (BH) of their resin-bonded permanent magnets are achieved by means of additional ball-milling at 293 K.
2. Experimental methods In order to prepare nitrides and carbides, the samples of Sm Fe V were pulverized into fine powder with an average particle size of about 15 lm. The gas-phase reaction between the alloy powder and nitrogen or acetylene was performed by heating the fine powder in nitrogen or acetylene gas at an ambient pressure and at temperatures ranging from 803 to 823 K for about 3 h. In order to avoid the hydrogen being absorbed into the sample, the sample space was pumped before cool-
315
ing in carbonation. The X-ray diffraction (XRD) patterns and thermo-magnetic analysis (TMA) showed that all samples of Sm (Fe,V) N and Sm (Fe,V) C were good phased and crystal W lized in the Nd (Fe,Ti) -type structure as that of the parent compounds, except for an estimated amount of a-Fe inside. Magnetic balance method (MBM) in a field of 1.2 T on the loose powder was used to examining the amount of the impurity phase a-Fe in nitrided and carbonated powder samples. The thermo-magnetic curve M(¹) for each free powder sample of Sm (Fe,V) and its nitride and carbide was, respectively, measured with a vibrating-sample magnetometer (VSM) in a low field of 0.04 T from 1.5 K to above Curie temperature. The Curie temperature ¹ was determined from M—¹ ! plot, which was derived from M(¹), by extrapolating M to zero. The Curie temperature ¹ of ! Sm (Fe,V) N and Sm (Fe,V) C , respectively, W increased about 181 and 189 K comparing with the parent compound. The N concentration in the Sm Fe V N compounds was obtained from \V V W the mass difference before and after nitrogenation. The anisotropy direction was deduced from the XRD patterns of finely ground powder samples mixed with epoxy which were oriented in a magnetic field of about 1.2 T. The nitride and carbide powders were then ballmilled in petroleum ether using metal balls of 4—10 mm diameter with a sample-to-metal-ball weight ratio of 1 to 60. The magnetically aligned cylinder samples that were to be exposed to ballmilling, for various times t, were made by mixing the powders with about 50% epoxy resin, and then solidifying them in an applied field of about 1.2 T. The hysteresis loops of each sample were measured using a VSM at RT. The demagnetization factor was corrected according to the shape and size for each sample.
3. Results and discussion After nitrogenation the easy magnetization direction (EMD) of Sm Fe V changed into the b-axis from the easy-cone structure. Only Sm Fe V N shows the uniaxial anisotropy
316
X.-F. Han et al. / Journal of Magnetism and Magnetic Materials 192 (1999) 314 —320
Table 1 The monoclinic lattice parameters, a, b, c, and b, and the unit cell volume »"abc sin b used in the analysis of X-ray data with the A2/m space group, the X-ray density o estimated based on the lattice constants, and the expansion d»/» of the unit-cell volume upon nitrogenation and carbonation for Sm Fe V compounds Sm Fe V (N,C) \V V W
a (nm)
b (nm)
c (nm)
b (deg.)
» (nm)
o (g/cm)
d»/» (%)
Sm Fe V Sm Fe V N Sm Fe V C W
1.061 1.084 1.083
0.855 0.869 0.870
0.971 0.989 0.985
96.86 97.05 97.39
0.874 0.924 0.920
7.83 7.60 7.6
5.8 5.4
and other nitrides in the series of R Fe VN \V V (R"Y, Ce, Nd, Gd, Tb, and Dy) compounds display the easy-plane anisotropy. The quantitative analysis of the exchange and crystal-field interactions in R (Fe,Ti) and R (Fe,Ti) N (R"Nd W and Sm) showed that Sm (Fe,Ti) N nitride be W come uniaxial anisotropic for y*2 [30], which also compared well with our experimental results. Like Sm Fe V N , the Sm Fe V C com W pounds also shows the uniaxial anisotropy. Table 1 gives the crystallographic parameters, the unit cell volume », the X-ray density o estimated based on the lattice constants, and the expansion d»/» of the unit-cell volume upon nitrogenation and carbonation for Sm Fe V compounds investigated here. After nitrogenation and carbonation the relative volume expansion is about 5.8 and 5.4%. For examining the amount of the impurity phase a-Fe in powder samples, the magnetization as a function of temperature are measured with a MBM in a field of 1.2 T on the loose powder samples of Sm Fe V N and Sm Fe V C W in the temperature range from RT to above 900 K as shown in Fig. 1, where the loose powder samples are free to be reoriented in the applied magnetic field. It is shown that in contribution to the magnetization the main impurity phase in nitride and carbide powder samples comes from a-Fe, and other impurity phases can be neglected. It is well known that the saturation magnetization of pure iron, BCC-Fe, at RT and 4.2 K are 217.2 and 221.7 Am/kg, respectively, and the values of saturation magnetization of the pure iron can be roughly thought to change linearly with decreasing temperature from RT to 4.2 K. So the saturation
Fig. 1. Thermomagnetic curves for Sm Fe V N and Sm Fe V C in a field of 1.2 T. W
magnetization contributed by the impurity phase a-Fe at RT and 4.2 K can be approximately derived from M—¹ plots by extrapolating M from the high temperature (700—900 K) to RT and then to 4.2 K. As an example, the concentration of impurity phase a-Fe in the nitride powder sample of Sm Fe V N is approximately determined to be 9.7 wt%, derived from (21.1 Am/kg)/ (217.2 Am/kg). The value of 21.1 Am/kg is the saturation magnetization at RT contributed by the impurity phase a-Fe in the nitride powder sample, derived from M—¹ plots by linearly extrapolating M from the high temperature (700—900 K) to RT, whereas the saturation magnetization at 4.2 K contributed by the impurity phase a-Fe in the nitride powder sample can be obtained by (21.1 Am/kg)* (221.7 Am/kg)/(217.2 Am/kg)"21.5 Am/kg.
X.-F. Han et al. / Journal of Magnetism and Magnetic Materials 192 (1999) 314 —320
The concentration of the impurity phase a-Fe in the carbide powder sample of Sm Fe V C is W approximately examined as 15.3 wt%. The saturation magnetization M and anisot1 ropy field H are measured by means of a VSM with applied field strengths of up to 7 T at 4.2 K, and by a pulsed magnetic field (PMF) up to 10 T at RT for the magnetically aligned samples of Sm Fe V N and Sm Fe V C . The ac W tual saturation magnetization at 4.2 K and RT can be obtained after deducting the contribution of the impurity phase a-Fe in the samples. As an example, before and after deducting the contribution of the impurity phase a-Fe the saturation magnetization of Sm Fe V N at RT are 143.6 and 135.7 Am/kg, which derived from (143.6—21.1) Am/ (1—0.097) kg"135.7 Am/kg. The good intrinsic magnetic properties of Sm Fe V N (¹ "683 K, M (RT)"135.7 ! 1 Am/kg, and k H (RT)"6.7 T) and Sm Fe V C (¹ "691 K, M (RT)" 97.5 Am/kg) make W ! 1 us believe that the nitrides and carbides of Sm Fe V have good hard magnetic properties. \V V Fig. 2 shows the variation of hard magnetic properties of Sm Fe V N powder with ball milling time t. As the ball-milling time t increases, the saturation magnetization M of Sm Fe V N 1 almost decreases linearly. The value of M de1 creases to near 70% of the value for the non-milled powder when t"28 h as shown in Fig. 2a. The reason is that, by ball milling, the grains are broken and the crystalline structure in the surface of the particles is destroyed, so the main phase of Sm Fe V N decreases while the non-mag netic impurity appears. This was observed in the XRD patterns with different ball-milling time. The longer the ball-milling time t is, the worse the XRD pattern does. The remanence B of Sm Fe V N powder increases quickly at the initial stage of the ball milling, appears to have a plateau for milling times between t"1 and 12 h and reaches a maximum value of 0.94 T at 12 h, and then decreases slowly. The coercivity k H has a different feature G ! from the remanence. With increasing ball-milling time t, k H increases almost linearly until G ! t"24 h, reaches a plateau of about 0.75 T between t"24 and 32 h, and then decreases slowly. The energy product (BH) increases gradually from
317
Fig. 2. The variation of hard magnetic properties of Sm Fe V N powder with ball-milling time t at 293 K.
a small value at the beginning of the ball milling to a maximum value of 108.5 kJ/m when t"12 h, and then decreases slowly. Obviously, (BH) is
influenced by the coercivity, the remanence, and the shape of the demagnetization curve. A good resin-bonded magnet with a remanence B of 0.94 T, a coercivity k H of 0.53 T and an G ! energy product (BH) of 108.5 kJ/m was ob tained using the Sm Fe V N powder after ball-milling 12 h at 293 K.
318
X.-F. Han et al. / Journal of Magnetism and Magnetic Materials 192 (1999) 314 —320
Fig. 4. The typical hysteresis loops of Sm Fe V C powder W with a ball-milling time 6 and 24 h at 293 K.
Fig. 3. The variation of hard magnetic properties of Sm Fe V C powder with ball-milling time t at 293 K. W
Fig. 3 illustrates the variation of hard magnetic properties of Sm Fe V C powder with ball W milling time t. As the ball-milling time t increases, the saturation magnetization M of Sm Fe V C 1 W has no obvious change until t"28 h as shown in Fig. 3a. The remanence B of Sm Fe V C W powder also increases rapidly at the beginning of the ball milling, reaches a maximum value of 0.88 T at 6 h and then decreases slowly. The coercivity k H increases gradually from a small value at the G ! initial stage of the ball milling to a maximum value
of 0.25 T when t"24 h, and then decreases slowly. The energy product (BH) increases rapidly from
a small value at the beginning of the ball milling to a maximum value of 39.1 kJ/m when t"6 h, and then decreases slowly. As an example, Fig. 4 shows the typical hysteresis loops of Sm Fe V C W measured with a VSM at 293 K when ball-milling 6 and 24 h. A good resin-bonded magnet with a remanence B of 0.81 T, a coercivity k H of 0.25 T, and an G ! energy product (BH) of 37.0 kJ/m was obtained
using the Sm Fe V C powder after ball-mill W ing 24 h at 293 K. Table 2 gives the Curie temperature ¹ , the max! imum values of remanence B , the coercivity k H , G ! and the energy product (BH) for the nitride magnet Sm Fe V N and the carbide magnet Sm Fe V C . The hard magnetic parameters W for other associated nitride and carbide magnets of Sm Fe T (T"Ti [11—13] and Cr [21,28,29]) \V V are also listed in the table for reference.
4. Conclusions The good intrinsic magnetic properties of Sm Fe V N (¹ "683 K, M (RT)"135.7 ! 1 Am/kg, and k H (RT)"6.7 T) and Sm Fe V C (¹ "691 K, M (RT)"97.5 Am/kg) make W ! 1
X.-F. Han et al. / Journal of Magnetism and Magnetic Materials 192 (1999) 314 —320
319
Table 2 The Curie temperature ¹ , the maximum values of remanence B , the coercivity k H , and the energy product (BH) for the nitride and ! G ! carbide magnets of Sm Fe V and other associated nitride and carbide magnets of Sm Fe T (T"Ti and Cr) \V V Magnets
¹ ! (K)
B (RT) (T)
k H (RT) G ! (T)
(BH) (RT)
(kJ/m)
Refs.
Sm Fe V N Sm Fe V C W Sm Fe Ti N W Sm Fe Ti C W Sm Fe Cr N W Sm Fe Cr N W Sm Fe Cr C W
683 691 750 641
0.94 0.88 1.04
0.75 0.25 0.83 0.3 0.65 0.79 0.80
108.5 39.1 105
This work This work [11,12] [13] [21] [28] [29]
686 559
0.84 0.86 0.80
these compounds the hopeful candidates for new high-performance permanent magnets. As a preliminary result for the resin-bonded permanent magnets of Sm Fe V N and Sm Fe V C , W the maximum values of remanence B of 0.94 and 0.88 T, the coercivity k H of 0.75 and 0.25 T, and G ! the energy product (BH) of 108.5 and 39.1 kJ/m are achieved by means of additional ball-milling at 293 K, respectively. The hard magnetic properties of Sm Fe V N at RT is better than that of Sm Fe V C in the present research results. W Acknowledgements Project supported by the State Committee of Science and Technology and the National Natural Science Foundation of China, and in part by National Key Laboratory of Theoretical Computational Chemistry, Jilin University.
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