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Microstructure and magnetic properties of nanocrystalline Fe–Zr–B alloy
Journal of Magnetism and Magnetic Materials 239 (2002) 506–508
Microstructure and magnetic properties of nanocrystalline Fe–Zr–B alloy b ! M. Hasiaka,b,*, M. Miglierinic, Y. Yamashiroa, W.H. Ciurzynska , H. Fukunagad a
Faculty of Engineering, Department of Electrical and Electronics, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan b Institute of Physics, Technical University of Czestochowa, Al. Armii Krajowej 19, 42-200 Czestochowa, Poland c Department of Nuclear Physics and Technology, Slovak University of Technology, Ilkovicova 3, 812 19 Bratislava, Slovakia d Faculty of Engineering, Nagasaki University, Nagasaki 852-8521, Japan
Abstract The microstructure and soft magnetic properties have been studied for the nanocrystalline Fe86Zr6B8 alloy. It was stated that the ribbon of the Fe86Zr6B8 alloy with 60% amount of the crystalline a-Fe phase exhibits good soft magnetic properties. The differences in the crystallization on the surface and in the bulk for the nanocrystalline Fe86Zr6B8 alloy . are studied using Mossbauer spectroscopy. r 2002 Elsevier Science B.V. All rights reserved. . Keywords: Nanocrystalline materials; Mossbauer spectroscopy; Permeability; Coercivity; Core losses
Nanocrystalline Fe–Zr–B alloys obtained by a controlled crystallization of melt spun amorphous ribbons exhibit excellent soft magnetic properties [1,2]. These alloys consist of a-Fe grains embedded in a residual amorphous matrix [3]. The ultra-fine grain structure leads to excellent soft magnetic properties (e.g. high saturation magnetization, low coercivity and low core loss). It has been reported in several papers [4,5] that the magnetic properties of Fe-based alloys depend on their composition, preparation conditions and cooling rate. In this paper, we study the structure and magnetic properties of the Fe86Zr6B8 alloy with different amounts of the crystalline phase. Amorphous ribbons of the Fe86Zr6B8 alloy were produced by a single roller melt-spinning technique in an Ar atmosphere. The width and the thickness of the investigated ribbons were about 3 mm and 28 mm, respectively. The nanocrystalline state was obtained by annealing of the as-quenched precursors at various temperatures for 1 h with a heating and cooling rate of dT=dt ¼ 10 K/min in a vacuum of 0.01 Pa. The microstructure of the ribbons and surface properties were *Corresponding author. Tel.: +81-98-895-8683; fax: +8198-895-8708. E-mail address: [email protected] (M. Hasiak).
. examined by Mossbauer spectrometry in transmission geometry and using conversion electrons (CEMS), respectively. 57Co(Rh) source was employed at room temperature. DC and AC magnetic measurements were performed for 10 cm long ribbons using M2H Loop Tracer (Tesla Co., Ltd.) and MMS-4001 (Ryowa Electronics Co., Ltd.), respectively. Differences between structures of the surface and the bulk in a magnetic material affect the resulting material . properties. Representative Mossbauer spectra taken by CEMS and transmission technique and corresponding hyperfine field distributions for the Fe86Zr6B8 alloy after annealing at 760 K for 1 h are shown in Fig. 1. . Mossbauer spectra consist of sharp lines in addition to distributed components. The former correspond to the crystalline a-Fe phase (Figs 1a and c). The latter are assigned to intergranular Fe atoms as well as to atoms located on the surface of nanocrystalline BCC-Fe grains that are in close contact with the amorphous surrounding, the so-called interface zone. Structural model adopted for the spectra evaluation is described in more details elsewhere [6]. Numerical analysis of the M. ossbauer spectra provided crystalline contents of 80% and 60% for the surface and the bulk of nanocrystalline ribbons, respectively. Average hyperfine fields at 57Fe nuclei are almost the same in the frame of an
0304-8853/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 1 ) 0 0 6 8 7 - 4
507
M. Hasiak et al. / Journal of Magnetism and Magnetic Materials 239 (2002) 506–508
P(B) (a.u.)
75
60
1.00
(c)
1.00
0.95
-5
0
v (mm/s)
5
(d)
0
15
100 • µe
1.05
20
90
(b)
10
10 • Hc (A/m)
(a)
45
P(B) (a.u.)
Relative transmission
Relative emission
1.10
5 30
720
740
760
780
800
820
Tann (K)
10
20
30
B (T)
Fig. 2. Effective permeability (me ) at 50 Hz and 60 A/m, and coercivity (Hc ) of the Fe86Zr6B8 alloy as a function of annealing temperature ðTann Þ for 1 h.
. Fig. 1. CEMS (a,b) and transmission (c,d) Mossbauer spectra and corresponding hyperfine field distribution PðBÞ; respectively, for the Fe86Zr6B8 alloy after annealing at 760 K for 1 h taken at room temperature.
10
1
d
-1
W (W • kg )
experimental error and equals 33.1 and 33.0 T for CEMS and transmission geometry, respectively. Two distinct components are clearly seen in PðBÞ distributions in Figs 1b and d. For CEMS measurements (Fig. 1b), the peaks are positioned at about 8 and 30 T. The first component (low field) corresponds to the amorphous residual matrix whereas the high field component represents the interface zone atoms. PðBÞ distribution corresponding to the transmission spectrum, i.e. to the bulk of nanocrystalline Fe86Zr6B8 alloy (Fig. 1d), depicts more complicated structure. The low field component is positioned at slightly higher B-value of about 10 T. The observed changes are due to different contents of disordered structural positions of the resonant Fe atoms in the bulk of the nanocrystalline sample with respect to its surface. A complex magnetic behavior is demonstrated by magnetic fields in the range of 15–25 T. They are mostly due to magnetic interactions between the crystalline grains that are transmitted into the amorphous rest [7]. The microstructure of the investigated samples influences their magnetic properties. Fig. 2 shows effective permeability and coercivity of the Fe86Zr6B8 alloy annealed at different temperatures. The effective permeability increases and coercivity decreases with increasing annealing temperature up to 760 K. The amount of a-Fe phase in the bulk of the 760 K annealed Fe86Zr6B8 alloy equals 60%. After annealing at higher temperatures, a dramatic increase in coercivity and a decrease in permeability is observed. These results revealed that the Fe86Zr6B8 alloy with 60% of crystalline a-Fe phase exhibits the best soft magnetic properties. Fig. 3 shows a relation between core losses and maximum flux density for the Fe86Zr6B8 alloy with different amounts of crystalline phase. As can be seen from this figure, the sample annealed at 760 K (Fig. 3b)
102
10
0
c a
10-1
10-2 0.1
b
0.5 B (T)
1
Fig. 3. Relation between core losses (W) and induction (B) for the Fe86Zr6B8 alloy after annealing for 1 h at: 720 K (a); 760 K (b); 820 K (c) and 1020 K (d), measured at the frequency of 50 Hz.
is characterized by the lowest core losses, which is connected with stress relief due to annealing out of some structural defects. With increasing amount of crystalline phase above 60%, an increase in core losses is observed. Moreover, after annealing at 1020 K (this is already above the secondary crystallization temperatures of 1005 K [5]), the formation of Fe3Zr phase was observed. Fig. 4 shows core losses at various frequencies versus the maximum induction for the Fe86Zr6B8 alloy annealed at 760 K. The core losses increase monotonically with the induction and for higher frequencies eddy currents dominate the losses. Moreover, except for the static hysteresis losses evaluated from the area of a DC M2H loop, we can distinguish classical eddy current losses and
508
M. Hasiak et al. / Journal of Magnetism and Magnetic Materials 239 (2002) 506–508
The nanocrystalline Fe86Zr6B8 alloy obtained by annealing at the temperature of 760 K for 1 h contains 60% of crystalline a-Fe phase and exhibits high saturation magnetic flux density of about 1.58 T and . very low core losses. Mossbauer effect investigations revealed microstructural as well as magnetic differences of the surface and the bulk of the nanocrystalline ribbon.
102 f = 1 kHz 1
10
-1 W (W • kg )
f = 250 Hz
100
10
f = 50 Hz
-1
Acknowledgements This work was supported by the grants 1/8305/01 and Franc/Slov/1.
10- 2
10- 3 0.01
0.1 B (T)
1
Fig. 4. Core losses (W) versus maximum induction field (B) at various frequencies for the Fe86Zr6B8 alloy annealed at 760 K for 1 h.
also anomalous eddy current losses, which are connected with the domain structure. Effective permeability of the Fe86Zr6B8 alloy annealed at 760 K under magnetic field of 60 A/m keeps a constant value of about 8500 in the frequency range 0.05–2 kHz. The cut off frequency, where a real part of the permeability has an inflection and an imaginary part of the permeability has a peak, is about 4 kHz.
References [1] K. Suzuki, A. Makino, A. Inoue, T. Masumoto, J. Appl. Phys. 70 (1991) 6232. [2] K. Suzuki, J.M. Cadogan, V. Sahajwalla, A. Inoue, T. Masumoto, J. Appl. Phys. 79 (1996) 5149. [3] M. Muller, . H. Grahl, N. Mattern, U. Kuhn, . Mater. Sci. Eng. A 226–228 (1997) 565. [4] A. Makino, T. Hatanai, A. Inoue, T. Masumoto, Mater. Sci. Eng. A 226–228 (1997) 594. ! [5] M. Hasiak, W.H. Ciurzynska, Y. Yamashiro, H. Fukunaga, K. Yamamoto, IEEE Trans. Magn., in press. [6] M. Miglierini, J.M. Gren"eche, J. Phys.: Condens. Matter. 9 (1997) 2303. [7] M. Miglierini, J.M. Gren"eche, J. Phys.: Condens. Matter. 9 (1997) 2321.
Microstructure and magnetic properties of nanocrystalline Fe–Zr–B alloy b ! M. Hasiaka,b,*, M. Miglierinic, Y. Yamashiroa, W.H. Ciurzynska , H. Fukunagad a
Faculty of Engineering, Department of Electrical and Electronics, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan b Institute of Physics, Technical University of Czestochowa, Al. Armii Krajowej 19, 42-200 Czestochowa, Poland c Department of Nuclear Physics and Technology, Slovak University of Technology, Ilkovicova 3, 812 19 Bratislava, Slovakia d Faculty of Engineering, Nagasaki University, Nagasaki 852-8521, Japan
Abstract The microstructure and soft magnetic properties have been studied for the nanocrystalline Fe86Zr6B8 alloy. It was stated that the ribbon of the Fe86Zr6B8 alloy with 60% amount of the crystalline a-Fe phase exhibits good soft magnetic properties. The differences in the crystallization on the surface and in the bulk for the nanocrystalline Fe86Zr6B8 alloy . are studied using Mossbauer spectroscopy. r 2002 Elsevier Science B.V. All rights reserved. . Keywords: Nanocrystalline materials; Mossbauer spectroscopy; Permeability; Coercivity; Core losses
Nanocrystalline Fe–Zr–B alloys obtained by a controlled crystallization of melt spun amorphous ribbons exhibit excellent soft magnetic properties [1,2]. These alloys consist of a-Fe grains embedded in a residual amorphous matrix [3]. The ultra-fine grain structure leads to excellent soft magnetic properties (e.g. high saturation magnetization, low coercivity and low core loss). It has been reported in several papers [4,5] that the magnetic properties of Fe-based alloys depend on their composition, preparation conditions and cooling rate. In this paper, we study the structure and magnetic properties of the Fe86Zr6B8 alloy with different amounts of the crystalline phase. Amorphous ribbons of the Fe86Zr6B8 alloy were produced by a single roller melt-spinning technique in an Ar atmosphere. The width and the thickness of the investigated ribbons were about 3 mm and 28 mm, respectively. The nanocrystalline state was obtained by annealing of the as-quenched precursors at various temperatures for 1 h with a heating and cooling rate of dT=dt ¼ 10 K/min in a vacuum of 0.01 Pa. The microstructure of the ribbons and surface properties were *Corresponding author. Tel.: +81-98-895-8683; fax: +8198-895-8708. E-mail address: [email protected] (M. Hasiak).
. examined by Mossbauer spectrometry in transmission geometry and using conversion electrons (CEMS), respectively. 57Co(Rh) source was employed at room temperature. DC and AC magnetic measurements were performed for 10 cm long ribbons using M2H Loop Tracer (Tesla Co., Ltd.) and MMS-4001 (Ryowa Electronics Co., Ltd.), respectively. Differences between structures of the surface and the bulk in a magnetic material affect the resulting material . properties. Representative Mossbauer spectra taken by CEMS and transmission technique and corresponding hyperfine field distributions for the Fe86Zr6B8 alloy after annealing at 760 K for 1 h are shown in Fig. 1. . Mossbauer spectra consist of sharp lines in addition to distributed components. The former correspond to the crystalline a-Fe phase (Figs 1a and c). The latter are assigned to intergranular Fe atoms as well as to atoms located on the surface of nanocrystalline BCC-Fe grains that are in close contact with the amorphous surrounding, the so-called interface zone. Structural model adopted for the spectra evaluation is described in more details elsewhere [6]. Numerical analysis of the M. ossbauer spectra provided crystalline contents of 80% and 60% for the surface and the bulk of nanocrystalline ribbons, respectively. Average hyperfine fields at 57Fe nuclei are almost the same in the frame of an
0304-8853/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 1 ) 0 0 6 8 7 - 4
507
M. Hasiak et al. / Journal of Magnetism and Magnetic Materials 239 (2002) 506–508
P(B) (a.u.)
75
60
1.00
(c)
1.00
0.95
-5
0
v (mm/s)
5
(d)
0
15
100 • µe
1.05
20
90
(b)
10
10 • Hc (A/m)
(a)
45
P(B) (a.u.)
Relative transmission
Relative emission
1.10
5 30
720
740
760
780
800
820
Tann (K)
10
20
30
B (T)
Fig. 2. Effective permeability (me ) at 50 Hz and 60 A/m, and coercivity (Hc ) of the Fe86Zr6B8 alloy as a function of annealing temperature ðTann Þ for 1 h.
. Fig. 1. CEMS (a,b) and transmission (c,d) Mossbauer spectra and corresponding hyperfine field distribution PðBÞ; respectively, for the Fe86Zr6B8 alloy after annealing at 760 K for 1 h taken at room temperature.
10
1
d
-1
W (W • kg )
experimental error and equals 33.1 and 33.0 T for CEMS and transmission geometry, respectively. Two distinct components are clearly seen in PðBÞ distributions in Figs 1b and d. For CEMS measurements (Fig. 1b), the peaks are positioned at about 8 and 30 T. The first component (low field) corresponds to the amorphous residual matrix whereas the high field component represents the interface zone atoms. PðBÞ distribution corresponding to the transmission spectrum, i.e. to the bulk of nanocrystalline Fe86Zr6B8 alloy (Fig. 1d), depicts more complicated structure. The low field component is positioned at slightly higher B-value of about 10 T. The observed changes are due to different contents of disordered structural positions of the resonant Fe atoms in the bulk of the nanocrystalline sample with respect to its surface. A complex magnetic behavior is demonstrated by magnetic fields in the range of 15–25 T. They are mostly due to magnetic interactions between the crystalline grains that are transmitted into the amorphous rest [7]. The microstructure of the investigated samples influences their magnetic properties. Fig. 2 shows effective permeability and coercivity of the Fe86Zr6B8 alloy annealed at different temperatures. The effective permeability increases and coercivity decreases with increasing annealing temperature up to 760 K. The amount of a-Fe phase in the bulk of the 760 K annealed Fe86Zr6B8 alloy equals 60%. After annealing at higher temperatures, a dramatic increase in coercivity and a decrease in permeability is observed. These results revealed that the Fe86Zr6B8 alloy with 60% of crystalline a-Fe phase exhibits the best soft magnetic properties. Fig. 3 shows a relation between core losses and maximum flux density for the Fe86Zr6B8 alloy with different amounts of crystalline phase. As can be seen from this figure, the sample annealed at 760 K (Fig. 3b)
102
10
0
c a
10-1
10-2 0.1
b
0.5 B (T)
1
Fig. 3. Relation between core losses (W) and induction (B) for the Fe86Zr6B8 alloy after annealing for 1 h at: 720 K (a); 760 K (b); 820 K (c) and 1020 K (d), measured at the frequency of 50 Hz.
is characterized by the lowest core losses, which is connected with stress relief due to annealing out of some structural defects. With increasing amount of crystalline phase above 60%, an increase in core losses is observed. Moreover, after annealing at 1020 K (this is already above the secondary crystallization temperatures of 1005 K [5]), the formation of Fe3Zr phase was observed. Fig. 4 shows core losses at various frequencies versus the maximum induction for the Fe86Zr6B8 alloy annealed at 760 K. The core losses increase monotonically with the induction and for higher frequencies eddy currents dominate the losses. Moreover, except for the static hysteresis losses evaluated from the area of a DC M2H loop, we can distinguish classical eddy current losses and
508
M. Hasiak et al. / Journal of Magnetism and Magnetic Materials 239 (2002) 506–508
The nanocrystalline Fe86Zr6B8 alloy obtained by annealing at the temperature of 760 K for 1 h contains 60% of crystalline a-Fe phase and exhibits high saturation magnetic flux density of about 1.58 T and . very low core losses. Mossbauer effect investigations revealed microstructural as well as magnetic differences of the surface and the bulk of the nanocrystalline ribbon.
102 f = 1 kHz 1
10
-1 W (W • kg )
f = 250 Hz
100
10
f = 50 Hz
-1
Acknowledgements This work was supported by the grants 1/8305/01 and Franc/Slov/1.
10- 2
10- 3 0.01
0.1 B (T)
1
Fig. 4. Core losses (W) versus maximum induction field (B) at various frequencies for the Fe86Zr6B8 alloy annealed at 760 K for 1 h.
also anomalous eddy current losses, which are connected with the domain structure. Effective permeability of the Fe86Zr6B8 alloy annealed at 760 K under magnetic field of 60 A/m keeps a constant value of about 8500 in the frequency range 0.05–2 kHz. The cut off frequency, where a real part of the permeability has an inflection and an imaginary part of the permeability has a peak, is about 4 kHz.
References [1] K. Suzuki, A. Makino, A. Inoue, T. Masumoto, J. Appl. Phys. 70 (1991) 6232. [2] K. Suzuki, J.M. Cadogan, V. Sahajwalla, A. Inoue, T. Masumoto, J. Appl. Phys. 79 (1996) 5149. [3] M. Muller, . H. Grahl, N. Mattern, U. Kuhn, . Mater. Sci. Eng. A 226–228 (1997) 565. [4] A. Makino, T. Hatanai, A. Inoue, T. Masumoto, Mater. Sci. Eng. A 226–228 (1997) 594. ! [5] M. Hasiak, W.H. Ciurzynska, Y. Yamashiro, H. Fukunaga, K. Yamamoto, IEEE Trans. Magn., in press. [6] M. Miglierini, J.M. Gren"eche, J. Phys.: Condens. Matter. 9 (1997) 2303. [7] M. Miglierini, J.M. Gren"eche, J. Phys.: Condens. Matter. 9 (1997) 2321.