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Soft magnetic properties of NiFe compacted powder alloys
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 304 (2006) e730–e732 www.elsevier.com/locate/jmmm
Soft magnetic properties of NiFe compacted powder alloys D. Oleksˇ a´kova´a,, S. Rothb, P. Kolla´ra, J. Fu¨zera a
Institute of Physics, Faculty of Science, P.J.Sˇafa´rik University, Park Angelinum 9, 041 54 Kosˇice, Slovakia b IFW Dresden, Helmholtzstr. 20, Postfach 270016, 01069 Dresden, Germany Available online 20 March 2006
Abstract It is known that Ni–Fe based alloys (permalloys) are important soft magnetic materials, which have been widely applied in the field of electronic devices and industry. The most suitable permalloys for application exhibit low value of coercivity and magnetostriction (for about 80 at% Ni), high saturation magnetic induction (for about 50 at% Ni), higher electrical resistivity (for about 35 at% Ni). The aim of this work was to investigate the structure and magnetic properties of Ni81 Fe19 (wt%) compacted powder material in the form of small cylinders. r 2006 Elsevier B.V. All rights reserved. PACS: 75.50.Kj; 75.80.+q; 81.40.Rs Keywords: Permalloy; Bulk sample; Coercivity
1. Introduction The magnetic investigation of Ni–Fe alloys has a long lasting tradition. New technological methods of preparation and treatment open possibilities to prepare the materials with well-known chemical compositions, exhibiting novel physical properties. The name of permalloy has been given to a series of nickel–iron alloys so heat-treated as to have a initial permeability much larger than that of pure iron. Arnold and Elmer [1] announced the discovery of this material and gave a brief review of some its properties. Mechanical milling and mechanical alloying is a useful powder processing technique that can produce a variety of equilibrium and non-equilibrium alloy phases [2]. 2. Experimental We have prepared powders by mechanical milling of microcrystalline NiFe (81 wt% of Ni) ribbon, prepared by Corresponding author.
E-mail address: [email protected] (D. Oleksˇ a´kova´). URL: http://www.science.upjs.sk. 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.02.205
melt-spinning, in a high energy planetary ball mill (RETSCH PM4000 with hardened steel vials and balls). The milling was performed in the protective argon atmosphere with ball-to-powder mass ratio (BPMR) of 6:1 and with a speed of 180 rpm. We have prepared bulk samples from these milled powders in the form of cylinders with the parameters: height 2.5 mm, diameter 10 mm and weight approximately 2 g. The compaction was performed at a pressure of 800 MPa for 5 min at 500 and 600 C. In order to prevent oxidation and the presence of free gases in the compacted samples, the compaction was performed in the vacuum of 5 103 Pa. The cylinders were annealed at the temperature between 500 and 1200 C. The crystalline character of all the samples was investigated by X-ray diffraction (XRD) with Co-K a radiation (Philips PW 1050). The magnetization of the powder samples was measured by a vibrating sample magnetometer (VSM) in a magnetic field of 1 T. The temperature dependence of magnetization was measured using a Faraday magnetic balance. The coercivity of both the powder and the bulk samples was measured by a Fo¨rster Koerzimat at room temperature. The magnetostriction of the cylinder shaped samples was measured by the strain gauge method.
ARTICLE IN PRESS D. Oleksˇa´kova´ et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e730–e732
3. Results and discussion
80
10000 5000 0
bulk in the form of cylinder
Intensity (a.u.)
40
60
80
7500 5000 2500 0
100
120
powder milled 25 hours
20
40
60
80
1000 500 0
100
120
powder milled 1 hours
20
40
60 80 2θ (degrees)
100
Fig. 1. X-ray diffractograms for NiFe.
120
70 ribbon MS (A.m2.kg-1)
60 50 ribbon milled 25 hours 40 30 20 10 0 0
100
200 300 400 Temperature (°C)
500
600
Fig. 2. Thermomagnetic curves of the NiFe samples.
1750 bulk compacted at 500°C bulk compacted at 600°C milled ribbon
1500 Coercivity (A.m-1)
We have decided to investigate the alloy NiFe (81 wt% of Ni) because it is known that at a certain concentration of Ni (about 81%) these alloys have a near-to-zero magnetostriction [3]. We expected that in the near-to-zero magnetostrictive alloys the residual stresses induced during the milling and consolidation of the powder do not cause an additional magnetic anisotropy and the alloys have good soft magnetic properties [4]. After preparation of the NiFe cylinder sample we confirmed that the value of magnetostriction is near-tozero (approximately 2 ppm). Fig. 1 shows the X-ray diffractograms of powders milled for 1 h and 25 h and of a bulk sample prepared from powder, which was milled for 25 h. The XRD analysis revealed that the milling of the NiFe microcrystalline ribbon and the compaction of this powder have no significant influence on the structure of the material. The phase was identified as a NiFe solid solution. It is reported [5], that this phase is found for NiFe-alloys with 63–85% Ni (wt%) prepared by conventional casting. We assume that milling of the ribbon and compaction of the powder does not cause formation of any other phase. It means that NiFe alloy in the form of the ribbon and powder prepared by milling of this ribbon is single-phase. In contrast to the pure elements Ni–Fe mixture, which was mechanically alloyed in a vibratory micro-mill, different phases were created and/or disappeared during milling [6]. The temperature dependence of magnetization MðTÞ of the NiFe powder is shown in Fig. 2. The Curie temperature, T C , was determined from MðTÞ curves, fitting the data near T C to a critical law of the form MðTÞðT T C Þb with b ¼ 0:36 and extrapolating to MðTÞ ¼ 0. We found that T C for these samples is 550 C. It corresponds with the T C of the alloy of the same chemical composition prepared by conventional casting ð560 CÞ [7]. The behavior of all curves is monotonous without inflection points; which means the samples consist of only one magnetic phase.
20
e731
1250 1000 750 500 250 0 0
5
10 15 20 Time of milling (hours)
25
Fig. 3. Coercivity of powder and bulk samples.
In Fig. 3 the coercivity of the milled ribbon as a function of milling time is compared to that of bulk samples prepared from the powder milled for the same time and afterward compacted at two different temperatures ð500 C; 600 CÞ. The coercivity of the samples compacted at 600 C is lower than the coercivity of the samples compacted at 500 C for all milling times. The samples with lower coercivity, compacted at 600 C were annealed for temperatures ranging from 500 to 1200 C, see Fig. 4. An increase of the annealing temperature causes a decrease of the coercivity of the bulk samples, prepared by compaction of powder milled for various time. This decrease is caused by relaxation of internal residual stresses induced into the samples during mechanical milling and compaction process of the near-to-zero magnetostrictive material. The lowest value of the coercivity (11 A/m) was achieved for the sample annealed at 1200 C, comparable with the value of coercivity of the conventional permalloy (4 A/m) [8].
ARTICLE IN PRESS D. Oleksˇa´kova´ et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e730–e732
e732
400
of Ni) smaller and smaller particles of powder were created with increasing milling time. For these small particles, rotation of the magnetization vector is the dominant magnetization process. After compaction of the powder displacement of domain walls becomes more dominant and the value of the coercivity decreases to a value comparable with the value of coercivity of conventional permalloy [8].
200
Acknowledgment
Coercivity (A.m-1)
800 0°C 500°C 700°C 900°C 1200°C
600
This work was supported by Science and Technology Assistance Agency under the Contract no. APVT-20008404 and partially supported by VEGA 1/1021/04.
0 0
5
10 15 Time of milling (hours)
20
25
Fig. 4. Coercivity of cylinders compacted at 600 C after annealing at various temperatures.
4. Conclusions The aim of this work was to prepare bulk samples of the chemical compositions NiFe (81 wt% of Ni) in the form of cylinders from a single-phase system, which remains singlephase after compaction. We have prepared bulk samples in the form of the small cylinders with coercivity down to 11 A/m. By the mechanical milling of ribbon NiFe (81 wt%
References [1] H.D. Arnold, G.W. Elmer, J. Franklin Inst. 195 (1923) 621. [2] L.A. Dobrzan´ski, R. Nowosielski, A. Przybyl, J. Konieczny, J. Mater. Process. Technol. 162–163 (2005) 20. [3] S. Chikazumi, Physics of Ferromagnetism, Oxford University Press, Oxford, 1997. [4] S. Roth, A.R. Ferchmin, S. Kobe, Landolt/Bo¯ rnstein: Numerical Data and Functional Relationships in Science and Technology, 1994. [5] T.B. Massalski: Binary Alloy, Phase Diagram, second ed., vol. 2, ASM International, 1990. [6] D. Oleksˇ a´kova´, et al., Czechoslovak J. Phys. 54 (2004) 93. [7] T.F. Connolly, E.D. Copenhaver, Bibliography of Magnetic Materials and Tabulation of Magnetic Transition Temperature, 1970. [8] W.F. Randall, Nickel–iron alloys of high permeability with special reference to Mumetal. J. Inst. Electr. Engrs. 80 (10) (1937) 647.
Journal of Magnetism and Magnetic Materials 304 (2006) e730–e732 www.elsevier.com/locate/jmmm
Soft magnetic properties of NiFe compacted powder alloys D. Oleksˇ a´kova´a,, S. Rothb, P. Kolla´ra, J. Fu¨zera a
Institute of Physics, Faculty of Science, P.J.Sˇafa´rik University, Park Angelinum 9, 041 54 Kosˇice, Slovakia b IFW Dresden, Helmholtzstr. 20, Postfach 270016, 01069 Dresden, Germany Available online 20 March 2006
Abstract It is known that Ni–Fe based alloys (permalloys) are important soft magnetic materials, which have been widely applied in the field of electronic devices and industry. The most suitable permalloys for application exhibit low value of coercivity and magnetostriction (for about 80 at% Ni), high saturation magnetic induction (for about 50 at% Ni), higher electrical resistivity (for about 35 at% Ni). The aim of this work was to investigate the structure and magnetic properties of Ni81 Fe19 (wt%) compacted powder material in the form of small cylinders. r 2006 Elsevier B.V. All rights reserved. PACS: 75.50.Kj; 75.80.+q; 81.40.Rs Keywords: Permalloy; Bulk sample; Coercivity
1. Introduction The magnetic investigation of Ni–Fe alloys has a long lasting tradition. New technological methods of preparation and treatment open possibilities to prepare the materials with well-known chemical compositions, exhibiting novel physical properties. The name of permalloy has been given to a series of nickel–iron alloys so heat-treated as to have a initial permeability much larger than that of pure iron. Arnold and Elmer [1] announced the discovery of this material and gave a brief review of some its properties. Mechanical milling and mechanical alloying is a useful powder processing technique that can produce a variety of equilibrium and non-equilibrium alloy phases [2]. 2. Experimental We have prepared powders by mechanical milling of microcrystalline NiFe (81 wt% of Ni) ribbon, prepared by Corresponding author.
E-mail address: [email protected] (D. Oleksˇ a´kova´). URL: http://www.science.upjs.sk. 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.02.205
melt-spinning, in a high energy planetary ball mill (RETSCH PM4000 with hardened steel vials and balls). The milling was performed in the protective argon atmosphere with ball-to-powder mass ratio (BPMR) of 6:1 and with a speed of 180 rpm. We have prepared bulk samples from these milled powders in the form of cylinders with the parameters: height 2.5 mm, diameter 10 mm and weight approximately 2 g. The compaction was performed at a pressure of 800 MPa for 5 min at 500 and 600 C. In order to prevent oxidation and the presence of free gases in the compacted samples, the compaction was performed in the vacuum of 5 103 Pa. The cylinders were annealed at the temperature between 500 and 1200 C. The crystalline character of all the samples was investigated by X-ray diffraction (XRD) with Co-K a radiation (Philips PW 1050). The magnetization of the powder samples was measured by a vibrating sample magnetometer (VSM) in a magnetic field of 1 T. The temperature dependence of magnetization was measured using a Faraday magnetic balance. The coercivity of both the powder and the bulk samples was measured by a Fo¨rster Koerzimat at room temperature. The magnetostriction of the cylinder shaped samples was measured by the strain gauge method.
ARTICLE IN PRESS D. Oleksˇa´kova´ et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e730–e732
3. Results and discussion
80
10000 5000 0
bulk in the form of cylinder
Intensity (a.u.)
40
60
80
7500 5000 2500 0
100
120
powder milled 25 hours
20
40
60
80
1000 500 0
100
120
powder milled 1 hours
20
40
60 80 2θ (degrees)
100
Fig. 1. X-ray diffractograms for NiFe.
120
70 ribbon MS (A.m2.kg-1)
60 50 ribbon milled 25 hours 40 30 20 10 0 0
100
200 300 400 Temperature (°C)
500
600
Fig. 2. Thermomagnetic curves of the NiFe samples.
1750 bulk compacted at 500°C bulk compacted at 600°C milled ribbon
1500 Coercivity (A.m-1)
We have decided to investigate the alloy NiFe (81 wt% of Ni) because it is known that at a certain concentration of Ni (about 81%) these alloys have a near-to-zero magnetostriction [3]. We expected that in the near-to-zero magnetostrictive alloys the residual stresses induced during the milling and consolidation of the powder do not cause an additional magnetic anisotropy and the alloys have good soft magnetic properties [4]. After preparation of the NiFe cylinder sample we confirmed that the value of magnetostriction is near-tozero (approximately 2 ppm). Fig. 1 shows the X-ray diffractograms of powders milled for 1 h and 25 h and of a bulk sample prepared from powder, which was milled for 25 h. The XRD analysis revealed that the milling of the NiFe microcrystalline ribbon and the compaction of this powder have no significant influence on the structure of the material. The phase was identified as a NiFe solid solution. It is reported [5], that this phase is found for NiFe-alloys with 63–85% Ni (wt%) prepared by conventional casting. We assume that milling of the ribbon and compaction of the powder does not cause formation of any other phase. It means that NiFe alloy in the form of the ribbon and powder prepared by milling of this ribbon is single-phase. In contrast to the pure elements Ni–Fe mixture, which was mechanically alloyed in a vibratory micro-mill, different phases were created and/or disappeared during milling [6]. The temperature dependence of magnetization MðTÞ of the NiFe powder is shown in Fig. 2. The Curie temperature, T C , was determined from MðTÞ curves, fitting the data near T C to a critical law of the form MðTÞðT T C Þb with b ¼ 0:36 and extrapolating to MðTÞ ¼ 0. We found that T C for these samples is 550 C. It corresponds with the T C of the alloy of the same chemical composition prepared by conventional casting ð560 CÞ [7]. The behavior of all curves is monotonous without inflection points; which means the samples consist of only one magnetic phase.
20
e731
1250 1000 750 500 250 0 0
5
10 15 20 Time of milling (hours)
25
Fig. 3. Coercivity of powder and bulk samples.
In Fig. 3 the coercivity of the milled ribbon as a function of milling time is compared to that of bulk samples prepared from the powder milled for the same time and afterward compacted at two different temperatures ð500 C; 600 CÞ. The coercivity of the samples compacted at 600 C is lower than the coercivity of the samples compacted at 500 C for all milling times. The samples with lower coercivity, compacted at 600 C were annealed for temperatures ranging from 500 to 1200 C, see Fig. 4. An increase of the annealing temperature causes a decrease of the coercivity of the bulk samples, prepared by compaction of powder milled for various time. This decrease is caused by relaxation of internal residual stresses induced into the samples during mechanical milling and compaction process of the near-to-zero magnetostrictive material. The lowest value of the coercivity (11 A/m) was achieved for the sample annealed at 1200 C, comparable with the value of coercivity of the conventional permalloy (4 A/m) [8].
ARTICLE IN PRESS D. Oleksˇa´kova´ et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e730–e732
e732
400
of Ni) smaller and smaller particles of powder were created with increasing milling time. For these small particles, rotation of the magnetization vector is the dominant magnetization process. After compaction of the powder displacement of domain walls becomes more dominant and the value of the coercivity decreases to a value comparable with the value of coercivity of conventional permalloy [8].
200
Acknowledgment
Coercivity (A.m-1)
800 0°C 500°C 700°C 900°C 1200°C
600
This work was supported by Science and Technology Assistance Agency under the Contract no. APVT-20008404 and partially supported by VEGA 1/1021/04.
0 0
5
10 15 Time of milling (hours)
20
25
Fig. 4. Coercivity of cylinders compacted at 600 C after annealing at various temperatures.
4. Conclusions The aim of this work was to prepare bulk samples of the chemical compositions NiFe (81 wt% of Ni) in the form of cylinders from a single-phase system, which remains singlephase after compaction. We have prepared bulk samples in the form of the small cylinders with coercivity down to 11 A/m. By the mechanical milling of ribbon NiFe (81 wt%
References [1] H.D. Arnold, G.W. Elmer, J. Franklin Inst. 195 (1923) 621. [2] L.A. Dobrzan´ski, R. Nowosielski, A. Przybyl, J. Konieczny, J. Mater. Process. Technol. 162–163 (2005) 20. [3] S. Chikazumi, Physics of Ferromagnetism, Oxford University Press, Oxford, 1997. [4] S. Roth, A.R. Ferchmin, S. Kobe, Landolt/Bo¯ rnstein: Numerical Data and Functional Relationships in Science and Technology, 1994. [5] T.B. Massalski: Binary Alloy, Phase Diagram, second ed., vol. 2, ASM International, 1990. [6] D. Oleksˇ a´kova´, et al., Czechoslovak J. Phys. 54 (2004) 93. [7] T.F. Connolly, E.D. Copenhaver, Bibliography of Magnetic Materials and Tabulation of Magnetic Transition Temperature, 1970. [8] W.F. Randall, Nickel–iron alloys of high permeability with special reference to Mumetal. J. Inst. Electr. Engrs. 80 (10) (1937) 647.