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AC magnetic properties of the soft magnetic composites based on nanocrystalline Ni–Fe powders obtained by mechanical alloying
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 310 (2007) 2474–2476 www.elsevier.com/locate/jmmm
AC magnetic properties of the soft magnetic composites based on nanocrystalline Ni–Fe powders obtained by mechanical alloying I. Chicinasa,c,, O. Geoffroyb, O. Isnardc, V. Popb,d a
Materials Sciences and Technology Department, Technical University of Cluj-Napoca, 103-105 Muncii Avenue, 400641 Cluj-Napoca, Romania b Laboratoire Louis Ne´el, CNRS, Associe´ a` l’Universite´ Joseph Fourier, BP166, F-38042 Grenoble Cedex 9, France c Laboratoire de Cristallographie, CNRS, Associe´ a` l’Universite´ Joseph Fourier, BP166, F-38042 Grenoble Cedex 9, France d Faculty of Physics, Babes-Bolyai University, 400084 Cluj-Napoca, Romania Available online 27 November 2006
Abstract Nanocrystalline soft magnetic composite materials based on nanocrystalline Ni3Fe powder (D ¼ 17 nm) and (Ni3Fe+Fe) mixture have been produced by mechanical alloying. Composite materials have been prepared by covering the nanocrystalline particles with a dielectric polymer binder, then compacted into a toroidal shape and finally polymerized. The frequency dependence of the permeability and losses in the range 1–100 kHz and electrical resistivity were studied in correlation with the dielectric content, tores density and ferromagnetic powder type. r 2006 Elsevier B.V. All rights reserved. PACS: 75.50.Tt; 81.05.t; 81.07.Bc; 81.20.Ev Keywords: Soft magnetic materials; Composite materials; Nanocrystalline materials; Permeability; Core loss
Soft magnetic composite (SMC) materials, produced by powder metallurgy from soft ferromagnetic powders pressed together with a dielectric binder, have recently gained back interest as magnetic cores for electrical converters. Generally, these materials have worse magnetic properties than ferromagnetic-sintered ones, but they have high electrical resistivity, and consequently very small core losses, being from this point of view useful for highfrequency applications [1–3]. On the other hand, the nanocrystalline materials present very good properties as soft magnetic materials [4]. The SMC materials based on nanocrystalline ferromagnetic powder could present, looking to core losses, an improvement when compared with the usual nanocrystalline ribbons. In addition to our previous work [5], this paper presents the magnetic and electrical properties of the SMC materials Corresponding author. Materials Sciences and Technology Department, Technical University of Cluj-Napoca, 103-105 Muncii Avenue, 400641 Cluj-Napoca, Romania. Tel.: +40 264 401702; fax: +40 264 415054. E-mail address: [email protected] (I. Chicinas).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.11.019
based on nanocrystalline Ni3Fe powder, obtained by mechanical alloying (MA), and on (Ni3Fe+Fe-NiFe 50 at%) mixture, where Fe was added to increase the sample induction. The synthesis process of nanocrystalline Ni3Fe powder and its structural/magnetic characteristics were reported elsewhere [6]. For these experiments, a Ni3Fe powder obtained after 21 h of MA with a mean crystallite size of 1772 nm was used. The NiFe50 mixture was obtained by milling for 2 h the nanocrystalline Ni3Fe powders together with Fe powders, obtaining by this procedure Ni3Fe/Fe composite particles. As dielectric binder, an epoxy resin was used. SMC have been produced by covering the powder particles with a dielectric polymer binder, then compacted into a toroidal shape (inner diameter of 25 mm and outer diameter of 35 mm) and finally polymerized. Details of this procedure and of the technological parameters of the composite powders can be found in Ref. [5]. Ten composite materials have been obtained by varying the binder content and compacting pressure (Table 1). Magnetic properties were determined on the tores in AC magnetic field at a maximum flux density (Bmax ¼ 0.05, 0.1,
ARTICLE IN PRESS I. Chicinas et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 2474–2476
Binder content (wt%)
Compacting pressure (MPa) (Ni3Fe+Fe) ¼ NiFe50 mixture
28
500
26
400
24
300
µ
Ni3Fe powder
600
30
1 1.5 2 3
700 600, 700, 800 700 700
22
700 700 700 700
20
200
18
100
16 0
20
40
60 f (kHz)
80
100
P/f (J/m3)
Table 1 The composite materials obtained
2475
0
Fig. 2. Permeability and core losses as a function of the frequency at different maximum flux density for Ni3Fe (open symbols) and NiFe50 (solid symbols) tores (dielectric content—1 wt%, compacting pressure— 700 MPa).
1200 1000
P (W/kg)
800
Fig. 1. Hysteresis loops of the Ni3Fe and NiFe50 tores (dielectric content—1.5 wt%, compacting pressure—700 MPa).
0.2 and 0.3 T) up to a frequency of 100 kHz. Electrical resistivity was determined by electrical resistance measurements performed on the cylindrical shape compacts. The hysteresis loops of the Ni3Fe and NiFe50 SMC (for the 1.5 wt% samples, 700 MPa) are presented in Fig. 1. It is observed that the nanocrystalline SMC based on Ni3Fe have low coercivity (E300 A/m) and NiFe50 SMC have higher remanence and saturation as compared to the Ni3Fe SMC. Magnetic permeability and core losses as a function of the frequency for different maximum flux densities are shown in Fig. 2 for Ni3Fe and NiFe50 tores, having a dielectric content of 1 wt% and pressed at 700 MPa. If the magnetic permeability does not have very high values, its frequency dependence shows that up to 100 kHz the permeability does not present significant decrease. This fact suggests that the limiting frequency for these SMC could be very high. For NiFe50 SMC, the power losses are higher than those for Ni3Fe SMC, due to a higher induction. The eddy-current losses component for Ni3Fe tore (1 wt% dielectric, 700 MPa), calculated from plot P/f versus f is 0.9% for B ¼ 0.05 T and 1.9% for B ¼ 0.2 T, relative to the total power losses. The low eddy-current losses are a consequence of the high electrical resistivity of the tores (E2.2 O mm for Ni3Fe and E1.9 O mm for NiFe50 SMC, 4 orders of magnitude larger than the compact materials resistivity and 3 orders of magnitude
600 400 200 0
0.5
1
1.5
2
2.5
3
3.5
Dielectric content (wt%)
Fig. 3. Core losses as a function of dielectric content at different frequencies for Ni3Fe and NiFe50 tores (Bmax ¼ 0.1 T).
larger than the resistivity of Finemet-like nanocrystalline materials). The dependence of the core losses versus dielectric content at different frequencies for Bmax ¼ 0.1 T is shown in Fig. 3. It can be seen that both SMC (Ni3Fe and NiFe50) at frequencies greater than 20 kHz show a minimum of the power losses curves. In correlation with the initial permeability behaviour as a function of dielectric content [5], we can conclude that the optimum dielectric content is 1.5 wt%. The core losses as a function of the maximum flux density show a classical linear dependence in a double logarithmic plot for all frequencies and for both Ni3Fe [5] and NiFe50 SMC. By a long annealing (120 h) at 170 1C in Ar atmosphere, the initial permeability (of the Ni3Fe tore with 1.5 wt% dielectric and pressed at 700 MPa) was increased with 6.5%, as a consequence of the removal of the compactioninduced internal stresses. Also, the core losses were reduced by 8–18%, depending on Bmax and frequency [5].
ARTICLE IN PRESS 2476
I. Chicinas et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 2474–2476
The nanocrystalline SMC-based NiFe50 mixture shows higher power losses and coercivity and lower permeability as compared with nanocrystalline SMC based on Ni3Fe. The low values of the permeability and remanence induction can be explained by low relative densities of the tores (64–68%), due to the low compressibility of the Ni3Fe powder produced by MA and the positive dimensional variation after polymerisation (1.3–2.2%). The higher tores density could be obtained by an improvement of the Ni3Fe nanocrystalline powder compressibility by an incipient recrystallisation or by the isostatic compaction method. Also, by using a multi-components dielectric, it could be possible to reduce the elastic relaxation occurring upon polymerization [7]. The use of these new soft magnetic materials for the production of the magnetic cores for AC applications depends upon the improvement that will be achieved.
I. Chicinas and V. Pop would like to thank the University J. Fourier, the Region Rhoˆnes Alpes and the Romanian Ministry of Education and Research for financial support.
References [1] A. Kordecki, B. Weglinski, Powder Metall. 33 (1988) 151. [2] S. Atkinson, MPR, April 1998, pp. 12–16. [3] O. Krogen, P. Jansson, in: Proceedings of the 1998 PM World Congress, Granada, 1998, pp. 520–525. [4] C. Suryanarayana, Int. Mater. Rev. 40 (1995) 228. [5] I. Chicinas, O. Geoffroy, O. Isnard, V. Pop, J. Magn. Magn. Mater. 290–291 (2005) 1531. [6] V. Pop, O. Isnard, I. Chicinas, J. Alloys Compds. 361 (2003) 144. [7] I. Chicinas, E. Holczer, A. Sorcoi, in: Proceedings of the European Congress of Powder Metallurgy;, Nice 2 (2001) 262–267.
Journal of Magnetism and Magnetic Materials 310 (2007) 2474–2476 www.elsevier.com/locate/jmmm
AC magnetic properties of the soft magnetic composites based on nanocrystalline Ni–Fe powders obtained by mechanical alloying I. Chicinasa,c,, O. Geoffroyb, O. Isnardc, V. Popb,d a
Materials Sciences and Technology Department, Technical University of Cluj-Napoca, 103-105 Muncii Avenue, 400641 Cluj-Napoca, Romania b Laboratoire Louis Ne´el, CNRS, Associe´ a` l’Universite´ Joseph Fourier, BP166, F-38042 Grenoble Cedex 9, France c Laboratoire de Cristallographie, CNRS, Associe´ a` l’Universite´ Joseph Fourier, BP166, F-38042 Grenoble Cedex 9, France d Faculty of Physics, Babes-Bolyai University, 400084 Cluj-Napoca, Romania Available online 27 November 2006
Abstract Nanocrystalline soft magnetic composite materials based on nanocrystalline Ni3Fe powder (D ¼ 17 nm) and (Ni3Fe+Fe) mixture have been produced by mechanical alloying. Composite materials have been prepared by covering the nanocrystalline particles with a dielectric polymer binder, then compacted into a toroidal shape and finally polymerized. The frequency dependence of the permeability and losses in the range 1–100 kHz and electrical resistivity were studied in correlation with the dielectric content, tores density and ferromagnetic powder type. r 2006 Elsevier B.V. All rights reserved. PACS: 75.50.Tt; 81.05.t; 81.07.Bc; 81.20.Ev Keywords: Soft magnetic materials; Composite materials; Nanocrystalline materials; Permeability; Core loss
Soft magnetic composite (SMC) materials, produced by powder metallurgy from soft ferromagnetic powders pressed together with a dielectric binder, have recently gained back interest as magnetic cores for electrical converters. Generally, these materials have worse magnetic properties than ferromagnetic-sintered ones, but they have high electrical resistivity, and consequently very small core losses, being from this point of view useful for highfrequency applications [1–3]. On the other hand, the nanocrystalline materials present very good properties as soft magnetic materials [4]. The SMC materials based on nanocrystalline ferromagnetic powder could present, looking to core losses, an improvement when compared with the usual nanocrystalline ribbons. In addition to our previous work [5], this paper presents the magnetic and electrical properties of the SMC materials Corresponding author. Materials Sciences and Technology Department, Technical University of Cluj-Napoca, 103-105 Muncii Avenue, 400641 Cluj-Napoca, Romania. Tel.: +40 264 401702; fax: +40 264 415054. E-mail address: [email protected] (I. Chicinas).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.11.019
based on nanocrystalline Ni3Fe powder, obtained by mechanical alloying (MA), and on (Ni3Fe+Fe-NiFe 50 at%) mixture, where Fe was added to increase the sample induction. The synthesis process of nanocrystalline Ni3Fe powder and its structural/magnetic characteristics were reported elsewhere [6]. For these experiments, a Ni3Fe powder obtained after 21 h of MA with a mean crystallite size of 1772 nm was used. The NiFe50 mixture was obtained by milling for 2 h the nanocrystalline Ni3Fe powders together with Fe powders, obtaining by this procedure Ni3Fe/Fe composite particles. As dielectric binder, an epoxy resin was used. SMC have been produced by covering the powder particles with a dielectric polymer binder, then compacted into a toroidal shape (inner diameter of 25 mm and outer diameter of 35 mm) and finally polymerized. Details of this procedure and of the technological parameters of the composite powders can be found in Ref. [5]. Ten composite materials have been obtained by varying the binder content and compacting pressure (Table 1). Magnetic properties were determined on the tores in AC magnetic field at a maximum flux density (Bmax ¼ 0.05, 0.1,
ARTICLE IN PRESS I. Chicinas et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 2474–2476
Binder content (wt%)
Compacting pressure (MPa) (Ni3Fe+Fe) ¼ NiFe50 mixture
28
500
26
400
24
300
µ
Ni3Fe powder
600
30
1 1.5 2 3
700 600, 700, 800 700 700
22
700 700 700 700
20
200
18
100
16 0
20
40
60 f (kHz)
80
100
P/f (J/m3)
Table 1 The composite materials obtained
2475
0
Fig. 2. Permeability and core losses as a function of the frequency at different maximum flux density for Ni3Fe (open symbols) and NiFe50 (solid symbols) tores (dielectric content—1 wt%, compacting pressure— 700 MPa).
1200 1000
P (W/kg)
800
Fig. 1. Hysteresis loops of the Ni3Fe and NiFe50 tores (dielectric content—1.5 wt%, compacting pressure—700 MPa).
0.2 and 0.3 T) up to a frequency of 100 kHz. Electrical resistivity was determined by electrical resistance measurements performed on the cylindrical shape compacts. The hysteresis loops of the Ni3Fe and NiFe50 SMC (for the 1.5 wt% samples, 700 MPa) are presented in Fig. 1. It is observed that the nanocrystalline SMC based on Ni3Fe have low coercivity (E300 A/m) and NiFe50 SMC have higher remanence and saturation as compared to the Ni3Fe SMC. Magnetic permeability and core losses as a function of the frequency for different maximum flux densities are shown in Fig. 2 for Ni3Fe and NiFe50 tores, having a dielectric content of 1 wt% and pressed at 700 MPa. If the magnetic permeability does not have very high values, its frequency dependence shows that up to 100 kHz the permeability does not present significant decrease. This fact suggests that the limiting frequency for these SMC could be very high. For NiFe50 SMC, the power losses are higher than those for Ni3Fe SMC, due to a higher induction. The eddy-current losses component for Ni3Fe tore (1 wt% dielectric, 700 MPa), calculated from plot P/f versus f is 0.9% for B ¼ 0.05 T and 1.9% for B ¼ 0.2 T, relative to the total power losses. The low eddy-current losses are a consequence of the high electrical resistivity of the tores (E2.2 O mm for Ni3Fe and E1.9 O mm for NiFe50 SMC, 4 orders of magnitude larger than the compact materials resistivity and 3 orders of magnitude
600 400 200 0
0.5
1
1.5
2
2.5
3
3.5
Dielectric content (wt%)
Fig. 3. Core losses as a function of dielectric content at different frequencies for Ni3Fe and NiFe50 tores (Bmax ¼ 0.1 T).
larger than the resistivity of Finemet-like nanocrystalline materials). The dependence of the core losses versus dielectric content at different frequencies for Bmax ¼ 0.1 T is shown in Fig. 3. It can be seen that both SMC (Ni3Fe and NiFe50) at frequencies greater than 20 kHz show a minimum of the power losses curves. In correlation with the initial permeability behaviour as a function of dielectric content [5], we can conclude that the optimum dielectric content is 1.5 wt%. The core losses as a function of the maximum flux density show a classical linear dependence in a double logarithmic plot for all frequencies and for both Ni3Fe [5] and NiFe50 SMC. By a long annealing (120 h) at 170 1C in Ar atmosphere, the initial permeability (of the Ni3Fe tore with 1.5 wt% dielectric and pressed at 700 MPa) was increased with 6.5%, as a consequence of the removal of the compactioninduced internal stresses. Also, the core losses were reduced by 8–18%, depending on Bmax and frequency [5].
ARTICLE IN PRESS 2476
I. Chicinas et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 2474–2476
The nanocrystalline SMC-based NiFe50 mixture shows higher power losses and coercivity and lower permeability as compared with nanocrystalline SMC based on Ni3Fe. The low values of the permeability and remanence induction can be explained by low relative densities of the tores (64–68%), due to the low compressibility of the Ni3Fe powder produced by MA and the positive dimensional variation after polymerisation (1.3–2.2%). The higher tores density could be obtained by an improvement of the Ni3Fe nanocrystalline powder compressibility by an incipient recrystallisation or by the isostatic compaction method. Also, by using a multi-components dielectric, it could be possible to reduce the elastic relaxation occurring upon polymerization [7]. The use of these new soft magnetic materials for the production of the magnetic cores for AC applications depends upon the improvement that will be achieved.
I. Chicinas and V. Pop would like to thank the University J. Fourier, the Region Rhoˆnes Alpes and the Romanian Ministry of Education and Research for financial support.
References [1] A. Kordecki, B. Weglinski, Powder Metall. 33 (1988) 151. [2] S. Atkinson, MPR, April 1998, pp. 12–16. [3] O. Krogen, P. Jansson, in: Proceedings of the 1998 PM World Congress, Granada, 1998, pp. 520–525. [4] C. Suryanarayana, Int. Mater. Rev. 40 (1995) 228. [5] I. Chicinas, O. Geoffroy, O. Isnard, V. Pop, J. Magn. Magn. Mater. 290–291 (2005) 1531. [6] V. Pop, O. Isnard, I. Chicinas, J. Alloys Compds. 361 (2003) 144. [7] I. Chicinas, E. Holczer, A. Sorcoi, in: Proceedings of the European Congress of Powder Metallurgy;, Nice 2 (2001) 262–267.