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Magnetic properties and intrinsic magnetic parameters of nanocrystalline Sm–Fe–N magnets
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) e1929–e1930
Magnetic properties and intrinsic magnetic parameters of nanocrystalline Sm–Fe–N magnets J.J. Wys"ockia, P. Pawlika,*, W. Kaszuwarab, M. Leonowiczb b
a Institute of Physics, Technical University of Cze)stochowa, Al. Armii Krajowej 19, Cze)stochowa, 42-200, Poland Department of Materials Science and Engineering, Warsaw University of Technology, ul. Wo!oska 141, Warsaw, 02-507, Poland
Abstract Intrinsic magnetic parameters of magnetic phases forming Sm–Fe–N magnet were determined. Additionally, the effect of grain size on magnetic properties (remanence Jr ; coercivity J Hc and energy product (BH)max) of the magnets produced by different methods (mechanical milling, mechanical alloying and HDDR process) and differing in phase composition was determined. r 2004 Elsevier B.V. All rights reserved. PACS: 75.50.Ww; 75.30.m Keywords: Magnetic properties; Rare-earth permanent magnets
Since the discovery of Sm2Fe17 nitride in 1990, this compound has become one of the most promising modern hard magnetic material, which exhibits outstanding magnetic properties. Many researchers have studied its magnetic properties and the number of articles on nanocrystalline Sm–Fe–N magnet is still increasing [1,2]. However, lack of reports on intrinsic magnetic parameters of particular magnetic phases forming Sm–Fe–N magnets is noticeable. Therefore, in this paper the intrinsic magnetic properties, such as: saturation magnetization Ms ; anisotropy constant K1 ; domain wall energy density g, domain wall width dB ; critical single-domain radius Rsd ; exchange constant A; exchange length lex ; coherence radius Rcoh ; magnetic hardness parameter k of the nanocrystalline Sm–Fe–N magnet and its constituent phases were determined. Additionally, the effect of grain size and the phase composition on magnetic proprieties (remanence Jr ; coercivity J Hc and maximum energy product (BH)max) of magnets produced by various methods (mechanical milling MM, mechanical alloying MA and HDDR process), was determined.
*Corresponding author. Tel./fax: +48-34-3250-795. E-mail address: [email protected] (P. Pawlik).
. X-ray diffraction and Mossbauer spectroscopy studies carried out on MM and MA processed Sm–Fe–N magnets revealed coexistence of two hard magnetic phases: Sm2Fe17N3 and SmFe7 and soft magnetic a-Fe phase. The phase concentrations varied for these magnets (see frame in Fig. 1). However, magnets produced by HDDR method consist only of Sm2Fe17N3 and a-Fe phases. The effect of grain size D on remanence Jr ; coercivity J Hc and maximum energy product (BH)max of nanocrystalline Sm–Fe–N magnets produced by MM, MA and HDDR methods with different phase content was shown in Fig. 1. Furthermore, the properties of the single-phase Sm2Fe17N3 magnet was shown for comparison in this figure. For all investigated samples, the remanence decreases with increase of the grain size. However, remanence is higher for samples containing higher volume fraction of the soft magnetic phase. Moreover, the coercivity of the magnet without a-Fe phase increases for the grain size in the range 10–40 nm, and then decreases with the decrease in the grain size. Such changes of coercivity values are related to the exchange coupling between hard magnetic grains. As the magnetic properties of investigated magnets are the resultant of their constituent phases, therefore
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.471
ARTICLE IN PRESS J.J. Wys!ocki et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1929–e1930
e1930
Sm2Fe17N3+ 31%α-Fe +12.2%SmFe7
Sm2Fe17N3+ 11%α-Fe
1.4
Sm2Fe17N3+ 3%α-Fe +12%SmFe7
1.2
Sm2Fe17N3
Jr [T]
1.0
Parameter
Sm–Fe–N magnet (MM)
0.8 0.6
m0Ms (T) A (pJ/m) K1 (MJ/m3) g (mJ/m2) dB (nm) lex (nm) Rcoh (nm) Rsd (nm) k
0.4 3
2
JHc
[MA/m]
Table 1 Basic magnetic parameters of nanocrystalline Sm–Fe–N magnet produced by MM method with 110 nm grain diameter and its constituent phases
1.63 4.3 5.2 18.9 2.8 1.4 6.8 80.6 2.0
Constituent phases Sm2Fe17N3
SmFe7
a-Fe
1.54 11.5 8.6 24.3 2.2 2.5 12.2 116.1 2.13
0.85 4.2 2.7 13.6 3.9 2.6 13.7 203.7 2.16
2.15 8.3 0.05 2.5 40 1.5 7.3 6.3 0.12
1
(BH)max
[kJ/m3]
120 100 80 60 40 20 0 0
20
40
60
80
100
120
D [nm]
Fig. 1. The effect of grain size D on remanence Jr ; coercivity J Hc and maximum energy product (BH)max of nanocrystalline Sm–Fe–N magnets produced by MM (+), HDDR (D) and MA ()methods with different phase composition. For comparison the properties of the single-phase Sm2Fe17N3 magnet are also shown (J).
determination of the magnetic properties of these phases seems to be a very useful and interesting problem. Applying the method proposed by Durst et al. [3] and developed by Wys"ocki [4], basic magnetic parameters of the Sm–Fe–N permanent magnet and its constituent phases were determined. As an example, calculations were performed for Sm–Fe–N samples (with 110 nm grain diameter), produced by MM method. In particular, the saturation magnetization for the SmFe7 phase, m0 Ms;ð2Þ ¼ 0:85 T was determined from equation Ms ¼ v1 Ms;ð1Þ þ v2 Ms;ð2Þ þ v3 Ms;ð3Þ ;
ð1Þ
where m0 Ms ¼ 1:63 T is the effective saturation magnetization of the Sm2Fe17N3/a-Fe magnet; m0 Ms;ð1Þ ¼ 1:54 T and m0 Ms;ð3Þ ¼ 2:15 T, are, respectively, the saturation magnetization of Sm2Fe17N3 and a-Fe phases. The volume fractions v1 ¼ 0:57; v2 ¼ 0:12; v3 ¼ 0:31 of particular phases (Sm2Fe17N3, SmFe7 and a-Fe, . respectively), were determined from Mossbauer spectra analysis. Similarly other magnetic parameters (A and K1 ) of the Sm2Fe17N3/a-Fe magnet and its constituent
phases were determined. Knowing the values of A; K1 and m0 Ms ; other intrinsic parameters such as: the exchange length lex ; the domain wall width dB ; the critical single-domain radius Rsd and the coherence length Rcoh [5], were determined. Moreover, the magnetic hardness parameter k ¼ 2:16 was calculated for the SmFe7 phase. According to Ref. [5] the criterion of hardening of the magnetic phase – k > 1; proves that the SmFe7 phase is magnetically hard. Additionally the domain wall energy g of the SmFe7 phase was determined. Calculated values of these parameters are listed in Table 1. From the data presented in Table 1 one can see that hard phases (Sm2Fe17N3 and SmFe7) have relatively large critical single domain radius Rsd but small values of lex and dB : Present studies allow to determine for the first time several basic magnetic parameters of SmFe7 hard magnetic phase forming the nanocrystalline Sm2Fe17N3/a-Fe magnet. This work was supported by Polish State Committee for Scientific Research under Grant No. PBZ KBN-013 T08 42.
References [1] M. Katter, New rare-earth-iron-based hard-magnetic materials, Technische Universit.at, Wien, 1991. . [2] R. Fischer, T. Schrefl, H. Kronmuller, J. Fidler, J. Magn. Magn. Mater. 153 (1996) 35. [3] K.-D. Durst, H. Kronm.uller, W. Ervens, Phys. Stat. Sol. (a) 108 (1988) 403. [4] J.J. Wys"ocki, Phys. Stat. Sol. (a) 153 (1996) 487. [5] R. Skomski, J.M.D. Coey, Permanent Magnetism, Institute of Physics Publishing, Bristol and Philadelphia, 1999.
Journal of Magnetism and Magnetic Materials 272–276 (2004) e1929–e1930
Magnetic properties and intrinsic magnetic parameters of nanocrystalline Sm–Fe–N magnets J.J. Wys"ockia, P. Pawlika,*, W. Kaszuwarab, M. Leonowiczb b
a Institute of Physics, Technical University of Cze)stochowa, Al. Armii Krajowej 19, Cze)stochowa, 42-200, Poland Department of Materials Science and Engineering, Warsaw University of Technology, ul. Wo!oska 141, Warsaw, 02-507, Poland
Abstract Intrinsic magnetic parameters of magnetic phases forming Sm–Fe–N magnet were determined. Additionally, the effect of grain size on magnetic properties (remanence Jr ; coercivity J Hc and energy product (BH)max) of the magnets produced by different methods (mechanical milling, mechanical alloying and HDDR process) and differing in phase composition was determined. r 2004 Elsevier B.V. All rights reserved. PACS: 75.50.Ww; 75.30.m Keywords: Magnetic properties; Rare-earth permanent magnets
Since the discovery of Sm2Fe17 nitride in 1990, this compound has become one of the most promising modern hard magnetic material, which exhibits outstanding magnetic properties. Many researchers have studied its magnetic properties and the number of articles on nanocrystalline Sm–Fe–N magnet is still increasing [1,2]. However, lack of reports on intrinsic magnetic parameters of particular magnetic phases forming Sm–Fe–N magnets is noticeable. Therefore, in this paper the intrinsic magnetic properties, such as: saturation magnetization Ms ; anisotropy constant K1 ; domain wall energy density g, domain wall width dB ; critical single-domain radius Rsd ; exchange constant A; exchange length lex ; coherence radius Rcoh ; magnetic hardness parameter k of the nanocrystalline Sm–Fe–N magnet and its constituent phases were determined. Additionally, the effect of grain size and the phase composition on magnetic proprieties (remanence Jr ; coercivity J Hc and maximum energy product (BH)max) of magnets produced by various methods (mechanical milling MM, mechanical alloying MA and HDDR process), was determined.
*Corresponding author. Tel./fax: +48-34-3250-795. E-mail address: [email protected] (P. Pawlik).
. X-ray diffraction and Mossbauer spectroscopy studies carried out on MM and MA processed Sm–Fe–N magnets revealed coexistence of two hard magnetic phases: Sm2Fe17N3 and SmFe7 and soft magnetic a-Fe phase. The phase concentrations varied for these magnets (see frame in Fig. 1). However, magnets produced by HDDR method consist only of Sm2Fe17N3 and a-Fe phases. The effect of grain size D on remanence Jr ; coercivity J Hc and maximum energy product (BH)max of nanocrystalline Sm–Fe–N magnets produced by MM, MA and HDDR methods with different phase content was shown in Fig. 1. Furthermore, the properties of the single-phase Sm2Fe17N3 magnet was shown for comparison in this figure. For all investigated samples, the remanence decreases with increase of the grain size. However, remanence is higher for samples containing higher volume fraction of the soft magnetic phase. Moreover, the coercivity of the magnet without a-Fe phase increases for the grain size in the range 10–40 nm, and then decreases with the decrease in the grain size. Such changes of coercivity values are related to the exchange coupling between hard magnetic grains. As the magnetic properties of investigated magnets are the resultant of their constituent phases, therefore
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.471
ARTICLE IN PRESS J.J. Wys!ocki et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1929–e1930
e1930
Sm2Fe17N3+ 31%α-Fe +12.2%SmFe7
Sm2Fe17N3+ 11%α-Fe
1.4
Sm2Fe17N3+ 3%α-Fe +12%SmFe7
1.2
Sm2Fe17N3
Jr [T]
1.0
Parameter
Sm–Fe–N magnet (MM)
0.8 0.6
m0Ms (T) A (pJ/m) K1 (MJ/m3) g (mJ/m2) dB (nm) lex (nm) Rcoh (nm) Rsd (nm) k
0.4 3
2
JHc
[MA/m]
Table 1 Basic magnetic parameters of nanocrystalline Sm–Fe–N magnet produced by MM method with 110 nm grain diameter and its constituent phases
1.63 4.3 5.2 18.9 2.8 1.4 6.8 80.6 2.0
Constituent phases Sm2Fe17N3
SmFe7
a-Fe
1.54 11.5 8.6 24.3 2.2 2.5 12.2 116.1 2.13
0.85 4.2 2.7 13.6 3.9 2.6 13.7 203.7 2.16
2.15 8.3 0.05 2.5 40 1.5 7.3 6.3 0.12
1
(BH)max
[kJ/m3]
120 100 80 60 40 20 0 0
20
40
60
80
100
120
D [nm]
Fig. 1. The effect of grain size D on remanence Jr ; coercivity J Hc and maximum energy product (BH)max of nanocrystalline Sm–Fe–N magnets produced by MM (+), HDDR (D) and MA ()methods with different phase composition. For comparison the properties of the single-phase Sm2Fe17N3 magnet are also shown (J).
determination of the magnetic properties of these phases seems to be a very useful and interesting problem. Applying the method proposed by Durst et al. [3] and developed by Wys"ocki [4], basic magnetic parameters of the Sm–Fe–N permanent magnet and its constituent phases were determined. As an example, calculations were performed for Sm–Fe–N samples (with 110 nm grain diameter), produced by MM method. In particular, the saturation magnetization for the SmFe7 phase, m0 Ms;ð2Þ ¼ 0:85 T was determined from equation Ms ¼ v1 Ms;ð1Þ þ v2 Ms;ð2Þ þ v3 Ms;ð3Þ ;
ð1Þ
where m0 Ms ¼ 1:63 T is the effective saturation magnetization of the Sm2Fe17N3/a-Fe magnet; m0 Ms;ð1Þ ¼ 1:54 T and m0 Ms;ð3Þ ¼ 2:15 T, are, respectively, the saturation magnetization of Sm2Fe17N3 and a-Fe phases. The volume fractions v1 ¼ 0:57; v2 ¼ 0:12; v3 ¼ 0:31 of particular phases (Sm2Fe17N3, SmFe7 and a-Fe, . respectively), were determined from Mossbauer spectra analysis. Similarly other magnetic parameters (A and K1 ) of the Sm2Fe17N3/a-Fe magnet and its constituent
phases were determined. Knowing the values of A; K1 and m0 Ms ; other intrinsic parameters such as: the exchange length lex ; the domain wall width dB ; the critical single-domain radius Rsd and the coherence length Rcoh [5], were determined. Moreover, the magnetic hardness parameter k ¼ 2:16 was calculated for the SmFe7 phase. According to Ref. [5] the criterion of hardening of the magnetic phase – k > 1; proves that the SmFe7 phase is magnetically hard. Additionally the domain wall energy g of the SmFe7 phase was determined. Calculated values of these parameters are listed in Table 1. From the data presented in Table 1 one can see that hard phases (Sm2Fe17N3 and SmFe7) have relatively large critical single domain radius Rsd but small values of lex and dB : Present studies allow to determine for the first time several basic magnetic parameters of SmFe7 hard magnetic phase forming the nanocrystalline Sm2Fe17N3/a-Fe magnet. This work was supported by Polish State Committee for Scientific Research under Grant No. PBZ KBN-013 T08 42.
References [1] M. Katter, New rare-earth-iron-based hard-magnetic materials, Technische Universit.at, Wien, 1991. . [2] R. Fischer, T. Schrefl, H. Kronmuller, J. Fidler, J. Magn. Magn. Mater. 153 (1996) 35. [3] K.-D. Durst, H. Kronm.uller, W. Ervens, Phys. Stat. Sol. (a) 108 (1988) 403. [4] J.J. Wys"ocki, Phys. Stat. Sol. (a) 153 (1996) 487. [5] R. Skomski, J.M.D. Coey, Permanent Magnetism, Institute of Physics Publishing, Bristol and Philadelphia, 1999.