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Magnetic properties of high-Bs Fe–Cu–Si–B nanocrystalline soft magnetic alloys
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 320 (2008) e750–e753 www.elsevier.com/locate/jmmm
Magnetic properties of high-Bs Fe–Cu–Si–B nanocrystalline soft magnetic alloys Motoki Ohta, Yoshihito Yoshizawa Advanced Electronics Research Laboratory, Hitachi Metals Ltd., Japan Available online 16 April 2008
Abstract In the present study, the magnetic properties and microstructures of newly developed Fe–Cu–Si–B alloys prepared by annealing the melt-spun ribbon have been studied. The average size and number density of nanocrystalline grains were about 20 nm and 1023–1024 m3, respectively. The saturation magnetic flux density Bs for the present alloy is more than 1.8 T, that is about 10% larger than that of Febased amorphous alloys. Moreover, core loss P of the present alloy is about half of that of Si-steel up to B ¼ 1.7 T. r 2008 Elsevier B.V. All rights reserved. PACS: 75.50.Tt; 75.50.Bb; 75.75.+a Keywords: Soft magnetic property; Fe-based nanocrystal; High Bs; Low core loss
1. Introduction Si-steels with high saturation magnetic flux density Bs are used for (magnetic) cores of transformers, motors and etc. [1–3]. However, further reduction of core loss is required for Si-steels. On the other hand, Fe-based amorphous alloys and/or Fe-based nanocrystalline materials have been extensively studied because they exhibit low core loss, and hence they are effective for energy saving and/or preservation of environment problem [4–8]. However, the size of core made by these materials becomes larger than that fabricated by Si-steel due to low Bs. From that viewpoint, the substitution of Fe for Co in Fe-based amorphous alloys is known as effective way for improving Bs. Fe–Co–B–Si amorphous alloys exhibit high performance as BsE1.8 T and low core loss [4]. However, since Co is an expensive element, Co-free alloys are expected for practical use. Therefore, development of Co-free Fe-based soft magnetic materials with lower core loss than Si-steel and higher Bs than Fe-based amorphous and/or nanocrystalline alloys are required. From this viewpoint, we have developed Fe–Cu–B and Fe–Cu–Si–B nanocrystalline alloys with a high Bs of 1.8 T and low coercive force Hc [9]. In the Corresponding author. Tel.: +81 48 531 1640; fax: +81 48 533 7102.
E-mail address: [email protected] (M. Ohta). 0304-8853/$ - see front matter r 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2008.04.064
present study, the ac magnetic properties of improved Fe–Cu–Si–B alloys have been studied. 2. Experimental Amorphous Fe80.5Cu1.5Si4B14 alloy ribbons were prepared by the single-roller melt-spinning technique. The width and thickness of the ribbons were 5 mm and 21 mm, respectively. The single-sheet specimens were annealed to induce nanocrystallization. The typical annealing conditions were at 410 1C for 60 min in a N2 atmosphere. The core specimens were fabricated by winding the ribbons into toroids with a 19 mm outer diameter and 15 mm inner diameter. These cores were annealed under a transverse magnetic field. The dc B–H curves were measured using a B–H curve tracer. Core losses were measured using a B–H analyzer. The microstructure was observed by a transmission electron microscopy (TEM). 3. Results and discussion In Fig. 1, magnetic field dependences (H) of magnetic flux density (B) for single-sheet and toroidal-core specimens are shown. B at 800 A/m (B800) and Hc are almost the same for both samples with B800 ¼ 1.76 T and Hc ¼ 6 A/m.
ARTICLE IN PRESS M. Ohta, Y. Yoshizawa / Journal of Magnetism and Magnetic Materials 320 (2008) e750–e753
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Table 1 Saturation magnetic flux density Bs, electrical resistively r and iron loss P15/50 at 1.5 T, 50 Hz, respectively, for single-sheet specimen of Fe80.5 Cu1.5Si4B14 nanocrystalline alloy and Si-steels and Fe-based amorphous alloy [3,5,10]
Fe80.5Cu1.5Si4B14 Grain-oriented Si-steel Fe–6.5 wt% Si-steel Fe-amorphous alloy
Bs (T)
r (mO m)
l ( 106)
1.80 2.03 1.80 1.57
0.8 0.5 0.8 1.3
12 0.8 0.1 30
Table 2 Iron loss P15/50 at 1.5 T, 50 Hz, P10/400 at 1.0 T, 400 Hz and P10/1k at 1.0 T, 1 kHz, respectively, for single-sheet Fe80.5Cu1.5Si4B14 nanocrystalline alloy and Si-steels and Fe-based amorphous alloy [3,5,10] Fig. 1. B–H curves for single-sheet and toroidal core of annealed Fe80.5Cu1.5Si4B14 alloy ribbons.
Fig. 2. B dependences of iron loss P at 50 Hz for the single-sheet specimen of Fe80.5Cu1.5Si4B14 nanocrystalline alloy, grain-oriented Si-steel and Febased amorphous alloy [3,5].
However, since toroidal-core specimen is annealed under transverse magnetic filed, the effect of induced magnetic anisotropy is observed in the slanted B–H curve of toroidal-core specimen. The induced magnetic anisotropy constant Ku is estimated as 115 J/m3. The B dependences of iron loss (P) at the frequency of 50 Hz of single-sheet specimen for Fe80.5Cu1.5Si4B14 nanocrystalline alloy are shown together with those for grainoriented Si-steel [3] and Fe-based amorphous alloys [5] in Fig. 2. As shown in Table 1, Bs is about 1.8 T, which is about 10% larger than that of the Fe-based amorphous alloy [5]. Note that the saturation magnetostriction in the present alloys is about 1/3 of those in Fe-based amorphous
Fe80.5Cu1.5Si4B14 Grain-oriented Si-steel Fe–6.5 wt% Si-steel Fe-amorphous alloy
P15/50 (W/kg)
P15/400 (W/kg)
P10/1k (W/kg)
0.26 0.59 – 0.11
2 6 6 2
6 27 19 6
alloys [5]. The electric resistivity r for present alloy is about 0.8 mO m, whereas that for grain-oriented Si-steel is about 0.5 mO m [3], therefore, the eddy current in the present alloys is suppressed. Moreover, the present alloy ribbon is more than 5 times thinner than grain-oriented Si-steels, and hence the eddy currents are greatly reduced. In Table 2, the core losses in several conditions are shown. Due to small loss of eddy currents, P at 1.5 T, 50 Hz (P15/50) for the present alloys is 2.6 W/kg and that is smaller than half of that for grain-oriented Si-steel. Especially in the high frequency region, the present alloy exhibits low iron loss. In Fig. 3, P vs. B curves with f ¼ 50 Hz for the toroidalcore specimen, grain-oriented Si-steel and Fe-based amorphous alloy are shown [3,5]. Owing to the induced magnetic anisotropy, the hysteresis loss is suppressed up to high B. The frequency (f) dependence of P for toroidalcore specimen is shown in Fig. 4 together with Fe–6.5 wt% Si-steels and Fe-based amorphous alloy [5,10]. The present alloy shows excellent f dependence of P up to high f. In Fig. 5, the TEM image of annealed Fe80.5Cu1.5Si4B14 alloy is shown. The micro-diffraction patterns of spot size of few nanometers are shown in the small window. The presence of bcc-Fe nanocrystalline grains is confirmed. The average grain size of these nanocrystalline grains is smaller than 20 nm. These nanocrystals are surrounded by amorphous matrix. It is considered that changed composition of this remaining amorphous matrix suppresses further growth of nanocrystalline grains in the annealing process. The number density of nanocrystals is about 1023–1024 m3, which is almost the same as the number density of Cu clusters in a Fe–Cu–Nb–Si–B nanocrystalline
ARTICLE IN PRESS e752
M. Ohta, Y. Yoshizawa / Journal of Magnetism and Magnetic Materials 320 (2008) e750–e753
Fig. 3. P vs. B curves at 50 Hz for the toroidal core of Fe80.5Cu1.5Si4B14 nanocrystalline alloy, grain-oriented Si-steel and Fe-based amorphous alloy [3,5].
Fig. 5. TEM image of annealed Fe80.5Cu1.5Si4B14 alloy is shown. The micro diffraction pattern of spot size of few nanometer is shown in the small window.
the excellent soft magnetic behavior. The present alloys are suitable for the use in high B and high f. 4. Conclusion
Fig. 4. P vs. f curves at B=0.2 T for toroidal core of Fe80.5Cu1.5Si4B14 nanocrystalline alloy, Fe–6.5 wt% Si-steel and Fe-based amorphous alloy [5,10].
alloy system estimated in an atom-probe study [11]. It has been pointed out that effective magnetocrystalline anisotropy increases with D in a nanocrystalline Fe–Cu–Nb– Si–B alloy system [12]. The smaller D is, the lower Hc becomes. The present alloys exhibit excellent magnetic saturation behavior in a low magnetic field due to their nanoscale structure. It should be pointed out that the present alloys contain over 95 wt% of Fe, that is about 10% higher than that in conventional Fe–Cu–Nb–Si–B nanocrystalline alloys. High Fe content brings about higher Bs. Moreover, nanocrystalline structure results in
In conclusion, we have produced nanocrystalline Fe– Cu–Si–B alloy obtained by annealing melt-spun ribbons. The magnetic properties and microstructure were discussed. Excellent magnetic properties such as a small P15/50 of 0.26 W/kg and a high Bs of more than 1.8 T were confirmed. The present nanocrystalline alloy exhibits lower iron loss from commercial frequency up to several tens of kHz than conventional high-Bs Fe-based alloys. Annealed specimens consist of bcc-Fe nanocrystals with average grain size of 20 nm and amorphous state. The number density of nanocrystals was about 1023–1024 m3. Such nanocrystalline structure brings about excellent soft magnetic characteristics. Moreover, high Fe content results in high Bs. References [1] N.P. Goss, Trans. Am. Soc. Met. 23 (1935) 515. [2] G.Y. Chin, J.H. Wernick, Ferromagnetic Materials, vol. 2, NorthHolland Physics, Amsterdam, 1980, p. 55. [3] D.F. Binns, A.B. Crompton, A. Jaberansari, IEE Proc. Pt C. Generation, Transm. Distrib. 133 (1986) 451. [4] J.A. Vaccari, Design Eng. 52 (1981) 53. [5] Y. Ogawa, M. Naoe, Y. Yoshizawa, R. Hasegawa, J. Magn. Magn. Mater. 304 (2006) e675.
ARTICLE IN PRESS M. Ohta, Y. Yoshizawa / Journal of Magnetism and Magnetic Materials 320 (2008) e750–e753 [6] Y. Yoshizawa, S. Oguma, K. Yamauchi, J. Appl. Phys. 64 (1988) 6044. [7] F.E. Luborsky, Ferromagnetic Materials, vol. 1, North-Holland, Amsterdam, 1980, p. 451. [8] Y. Yoshizawa, Scripta Mater. 44 (2001) 1321. [9] M. Ohta, Y. Yoshizawa, Jpn. J. Appl. Phys. 46 (2007) L477.
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[10] M. Abe, Y. Takada, T. Murakami, Y. Tanaka, Y. Mihara, J. Mater. Eng. 11 (1989) 109. [11] K. Hono, D.H. Ping, Materials Characterization, vol. 44, Elsevier, New York, 2000, p. 203. [12] G. Herzer, Handbook of Magnetic Materials, vol. 10, Elsevier, Amsterdam, 1997, p. 415.
Journal of Magnetism and Magnetic Materials 320 (2008) e750–e753 www.elsevier.com/locate/jmmm
Magnetic properties of high-Bs Fe–Cu–Si–B nanocrystalline soft magnetic alloys Motoki Ohta, Yoshihito Yoshizawa Advanced Electronics Research Laboratory, Hitachi Metals Ltd., Japan Available online 16 April 2008
Abstract In the present study, the magnetic properties and microstructures of newly developed Fe–Cu–Si–B alloys prepared by annealing the melt-spun ribbon have been studied. The average size and number density of nanocrystalline grains were about 20 nm and 1023–1024 m3, respectively. The saturation magnetic flux density Bs for the present alloy is more than 1.8 T, that is about 10% larger than that of Febased amorphous alloys. Moreover, core loss P of the present alloy is about half of that of Si-steel up to B ¼ 1.7 T. r 2008 Elsevier B.V. All rights reserved. PACS: 75.50.Tt; 75.50.Bb; 75.75.+a Keywords: Soft magnetic property; Fe-based nanocrystal; High Bs; Low core loss
1. Introduction Si-steels with high saturation magnetic flux density Bs are used for (magnetic) cores of transformers, motors and etc. [1–3]. However, further reduction of core loss is required for Si-steels. On the other hand, Fe-based amorphous alloys and/or Fe-based nanocrystalline materials have been extensively studied because they exhibit low core loss, and hence they are effective for energy saving and/or preservation of environment problem [4–8]. However, the size of core made by these materials becomes larger than that fabricated by Si-steel due to low Bs. From that viewpoint, the substitution of Fe for Co in Fe-based amorphous alloys is known as effective way for improving Bs. Fe–Co–B–Si amorphous alloys exhibit high performance as BsE1.8 T and low core loss [4]. However, since Co is an expensive element, Co-free alloys are expected for practical use. Therefore, development of Co-free Fe-based soft magnetic materials with lower core loss than Si-steel and higher Bs than Fe-based amorphous and/or nanocrystalline alloys are required. From this viewpoint, we have developed Fe–Cu–B and Fe–Cu–Si–B nanocrystalline alloys with a high Bs of 1.8 T and low coercive force Hc [9]. In the Corresponding author. Tel.: +81 48 531 1640; fax: +81 48 533 7102.
E-mail address: [email protected] (M. Ohta). 0304-8853/$ - see front matter r 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2008.04.064
present study, the ac magnetic properties of improved Fe–Cu–Si–B alloys have been studied. 2. Experimental Amorphous Fe80.5Cu1.5Si4B14 alloy ribbons were prepared by the single-roller melt-spinning technique. The width and thickness of the ribbons were 5 mm and 21 mm, respectively. The single-sheet specimens were annealed to induce nanocrystallization. The typical annealing conditions were at 410 1C for 60 min in a N2 atmosphere. The core specimens were fabricated by winding the ribbons into toroids with a 19 mm outer diameter and 15 mm inner diameter. These cores were annealed under a transverse magnetic field. The dc B–H curves were measured using a B–H curve tracer. Core losses were measured using a B–H analyzer. The microstructure was observed by a transmission electron microscopy (TEM). 3. Results and discussion In Fig. 1, magnetic field dependences (H) of magnetic flux density (B) for single-sheet and toroidal-core specimens are shown. B at 800 A/m (B800) and Hc are almost the same for both samples with B800 ¼ 1.76 T and Hc ¼ 6 A/m.
ARTICLE IN PRESS M. Ohta, Y. Yoshizawa / Journal of Magnetism and Magnetic Materials 320 (2008) e750–e753
e751
Table 1 Saturation magnetic flux density Bs, electrical resistively r and iron loss P15/50 at 1.5 T, 50 Hz, respectively, for single-sheet specimen of Fe80.5 Cu1.5Si4B14 nanocrystalline alloy and Si-steels and Fe-based amorphous alloy [3,5,10]
Fe80.5Cu1.5Si4B14 Grain-oriented Si-steel Fe–6.5 wt% Si-steel Fe-amorphous alloy
Bs (T)
r (mO m)
l ( 106)
1.80 2.03 1.80 1.57
0.8 0.5 0.8 1.3
12 0.8 0.1 30
Table 2 Iron loss P15/50 at 1.5 T, 50 Hz, P10/400 at 1.0 T, 400 Hz and P10/1k at 1.0 T, 1 kHz, respectively, for single-sheet Fe80.5Cu1.5Si4B14 nanocrystalline alloy and Si-steels and Fe-based amorphous alloy [3,5,10] Fig. 1. B–H curves for single-sheet and toroidal core of annealed Fe80.5Cu1.5Si4B14 alloy ribbons.
Fig. 2. B dependences of iron loss P at 50 Hz for the single-sheet specimen of Fe80.5Cu1.5Si4B14 nanocrystalline alloy, grain-oriented Si-steel and Febased amorphous alloy [3,5].
However, since toroidal-core specimen is annealed under transverse magnetic filed, the effect of induced magnetic anisotropy is observed in the slanted B–H curve of toroidal-core specimen. The induced magnetic anisotropy constant Ku is estimated as 115 J/m3. The B dependences of iron loss (P) at the frequency of 50 Hz of single-sheet specimen for Fe80.5Cu1.5Si4B14 nanocrystalline alloy are shown together with those for grainoriented Si-steel [3] and Fe-based amorphous alloys [5] in Fig. 2. As shown in Table 1, Bs is about 1.8 T, which is about 10% larger than that of the Fe-based amorphous alloy [5]. Note that the saturation magnetostriction in the present alloys is about 1/3 of those in Fe-based amorphous
Fe80.5Cu1.5Si4B14 Grain-oriented Si-steel Fe–6.5 wt% Si-steel Fe-amorphous alloy
P15/50 (W/kg)
P15/400 (W/kg)
P10/1k (W/kg)
0.26 0.59 – 0.11
2 6 6 2
6 27 19 6
alloys [5]. The electric resistivity r for present alloy is about 0.8 mO m, whereas that for grain-oriented Si-steel is about 0.5 mO m [3], therefore, the eddy current in the present alloys is suppressed. Moreover, the present alloy ribbon is more than 5 times thinner than grain-oriented Si-steels, and hence the eddy currents are greatly reduced. In Table 2, the core losses in several conditions are shown. Due to small loss of eddy currents, P at 1.5 T, 50 Hz (P15/50) for the present alloys is 2.6 W/kg and that is smaller than half of that for grain-oriented Si-steel. Especially in the high frequency region, the present alloy exhibits low iron loss. In Fig. 3, P vs. B curves with f ¼ 50 Hz for the toroidalcore specimen, grain-oriented Si-steel and Fe-based amorphous alloy are shown [3,5]. Owing to the induced magnetic anisotropy, the hysteresis loss is suppressed up to high B. The frequency (f) dependence of P for toroidalcore specimen is shown in Fig. 4 together with Fe–6.5 wt% Si-steels and Fe-based amorphous alloy [5,10]. The present alloy shows excellent f dependence of P up to high f. In Fig. 5, the TEM image of annealed Fe80.5Cu1.5Si4B14 alloy is shown. The micro-diffraction patterns of spot size of few nanometers are shown in the small window. The presence of bcc-Fe nanocrystalline grains is confirmed. The average grain size of these nanocrystalline grains is smaller than 20 nm. These nanocrystals are surrounded by amorphous matrix. It is considered that changed composition of this remaining amorphous matrix suppresses further growth of nanocrystalline grains in the annealing process. The number density of nanocrystals is about 1023–1024 m3, which is almost the same as the number density of Cu clusters in a Fe–Cu–Nb–Si–B nanocrystalline
ARTICLE IN PRESS e752
M. Ohta, Y. Yoshizawa / Journal of Magnetism and Magnetic Materials 320 (2008) e750–e753
Fig. 3. P vs. B curves at 50 Hz for the toroidal core of Fe80.5Cu1.5Si4B14 nanocrystalline alloy, grain-oriented Si-steel and Fe-based amorphous alloy [3,5].
Fig. 5. TEM image of annealed Fe80.5Cu1.5Si4B14 alloy is shown. The micro diffraction pattern of spot size of few nanometer is shown in the small window.
the excellent soft magnetic behavior. The present alloys are suitable for the use in high B and high f. 4. Conclusion
Fig. 4. P vs. f curves at B=0.2 T for toroidal core of Fe80.5Cu1.5Si4B14 nanocrystalline alloy, Fe–6.5 wt% Si-steel and Fe-based amorphous alloy [5,10].
alloy system estimated in an atom-probe study [11]. It has been pointed out that effective magnetocrystalline anisotropy increases with D in a nanocrystalline Fe–Cu–Nb– Si–B alloy system [12]. The smaller D is, the lower Hc becomes. The present alloys exhibit excellent magnetic saturation behavior in a low magnetic field due to their nanoscale structure. It should be pointed out that the present alloys contain over 95 wt% of Fe, that is about 10% higher than that in conventional Fe–Cu–Nb–Si–B nanocrystalline alloys. High Fe content brings about higher Bs. Moreover, nanocrystalline structure results in
In conclusion, we have produced nanocrystalline Fe– Cu–Si–B alloy obtained by annealing melt-spun ribbons. The magnetic properties and microstructure were discussed. Excellent magnetic properties such as a small P15/50 of 0.26 W/kg and a high Bs of more than 1.8 T were confirmed. The present nanocrystalline alloy exhibits lower iron loss from commercial frequency up to several tens of kHz than conventional high-Bs Fe-based alloys. Annealed specimens consist of bcc-Fe nanocrystals with average grain size of 20 nm and amorphous state. The number density of nanocrystals was about 1023–1024 m3. Such nanocrystalline structure brings about excellent soft magnetic characteristics. Moreover, high Fe content results in high Bs. References [1] N.P. Goss, Trans. Am. Soc. Met. 23 (1935) 515. [2] G.Y. Chin, J.H. Wernick, Ferromagnetic Materials, vol. 2, NorthHolland Physics, Amsterdam, 1980, p. 55. [3] D.F. Binns, A.B. Crompton, A. Jaberansari, IEE Proc. Pt C. Generation, Transm. Distrib. 133 (1986) 451. [4] J.A. Vaccari, Design Eng. 52 (1981) 53. [5] Y. Ogawa, M. Naoe, Y. Yoshizawa, R. Hasegawa, J. Magn. Magn. Mater. 304 (2006) e675.
ARTICLE IN PRESS M. Ohta, Y. Yoshizawa / Journal of Magnetism and Magnetic Materials 320 (2008) e750–e753 [6] Y. Yoshizawa, S. Oguma, K. Yamauchi, J. Appl. Phys. 64 (1988) 6044. [7] F.E. Luborsky, Ferromagnetic Materials, vol. 1, North-Holland, Amsterdam, 1980, p. 451. [8] Y. Yoshizawa, Scripta Mater. 44 (2001) 1321. [9] M. Ohta, Y. Yoshizawa, Jpn. J. Appl. Phys. 46 (2007) L477.
e753
[10] M. Abe, Y. Takada, T. Murakami, Y. Tanaka, Y. Mihara, J. Mater. Eng. 11 (1989) 109. [11] K. Hono, D.H. Ping, Materials Characterization, vol. 44, Elsevier, New York, 2000, p. 203. [12] G. Herzer, Handbook of Magnetic Materials, vol. 10, Elsevier, Amsterdam, 1997, p. 415.