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Effects of annealing on martensitic and magnetic transitions of Ni–Ga–Fe ferromagnetic shape memory alloys
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) 2043–2044
Effects of annealing on martensitic and magnetic transitions of Ni–Ga–Fe ferromagnetic shape memory alloys Katsunari Oikawaa,*, Toshihiro Omorib, Ryosuke Kainumab, Kiyohito Ishidab a
National Institute of Advanced Industrial Science and Technology, Tohoku Center, 4-2-1 Nigatake, Miyagino-ku, Sendai 983-8551, Japan b Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
Abstract Effects of annealing on the martensitic and magnetic transitions in Ni51Ga27Fe22 shape memory alloy were investigated. Curie temperature of the annealed sample decreased with increasing annealing temperature, related to degree of the L21 order, SL21 : Both martensitic starting Ms and the austenitic finishing Af temperatures increased with increasing annealing temperature and showed maxima by annealing at 873 K. The Ms and Af seemed to be affected by not only SL21 ; but also by this magnetic behavior. r 2003 Elsevier B.V. All rights reserved. PACS: 78.80.+q; 75.30.Gw; 81.30.Kf Keywords: Ferromagnetic; Shape memory alloy; Martensite; Order–disorder transition; Heusler alloy
Ferromagnetic shape memory alloys (FSMAs) have received much attention due to their potential for use as smart materials, because they show a large magneticfield-induced strain [1]. Several FSMAs have been developed, including Ni2MnGa [1], Fe–Pd [2], Fe–Pt [3], Ni2MnAl [4], and Co–Ni–Al [5,6] systems. Moreover, Ni–Fe–Al [7], Co–Ni–Ga [8] systems have been proposed as the new candidates of FSMAs. Recently, the present authors found promising FSMAs in Ni–Ga– Fe system [9,10]. The Ni–Ga–Fe alloys exhibit a martensitic transformation from a B2 or L21 austenite to a martensite phase with a 7-layer (14 M) or 5-layer (10 M) modulated structure. The principle features of magnetic properties of the 14 M phase in a Ni51:5 Fe22:0 Ga26:5 single crystal have been determined in our previous paper [11]. Recently, it was reported that the austenite phase of Ni–Fe–Ga alloys shows an order–disorder transition from the L21 to the B2 structure at 970 K [9]. It is expected that the magnetic properties and martensitic *Corresponding author. Tel.: +81-22-237-5211; fax: +8122-236-6839. E-mail address: [email protected] (K. Oikawa).
transformation of the ordered alloys significantly depend on the degree of atomic order. In the present study, the effects of annealing temperature on the martensitic and magnetic transitions in a Ni51Ga27Fe22 FSMA were investigated. The alloy ingot was prepared using a cold crucible levitation melting furnace under an argon atmosphere. The small specimens taken from the ingots were homogenized at 1473 K for 3 h and then quenched in ice water. The quenched samples were annealed from 473 to 1023 K for 1 h to promote atomic ordering in the L21 phase and then quenched in ice water. Thermomagnetization curve M2T was measured with a vibrating sample magnetometer at field strength of 500 Oe, and the Curie point Tc was taken as minimum point in the plot of the temperature derivative of magnetization. The martenstitic transition temperatures Ms and Af were determined by differential scanning calorimetry (DSC). Dependence of annealing temperature on the Ms ; Af as well as Tc is shown in Fig. 1. Tc of the annealed samples decreased considerably with increasing annealing temperature in the elevated temperature region over 750 K. According to the TEM observation, the ordered
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.548
ARTICLE IN PRESS K. Oikawa et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 2043–2044
2044 400
Temperature [K]
350 300 250
B2
L21
Tc 200
Ms Af
150 100 as-quench
450
550
650
750
850
950
1050
Annealing temperature [K]
Fig. 1. Annealing temperature dependence of Ms ; Af and Tc :
6 M [arb. unit]
473 K 4 martensitic transition
873 K phase transiton Curie cooling temperature heating
2
0 0
100
200 300 Temperature [K]
400
Fig. 2. Thermomagnetization curve on cooling and heating of the samples annealed at 473 and 873 K.
reflections f1 1 1gL21 in a sample annealed at 773 K were considerably stronger than those in an as-quenched sample, which shows that B2/L21 ordering is promoted by annealing at 773 K. It is clear that the degree of L21 order, SL21 may increase due to annealing at temperatures lower than 773 K, but decrease by annealing at higher temperatures which are close to the B2/L21 ordering temperature of 973 K. Thus, it can be concluded that the increase of Tc is due to the increase of SL21 : On the other hand, both Ms and Af increase with increasing annealing temperature and reach peaks by annealing at 873 K. Further elevating the annealing temperature reduces Ms and Af : From the tendency in the range of 873 to 1023 K, the Ms and Af are expected to increase with increasing SL21 : However, those of the samples annealed at 473 and 573 K were lower than that of the as-quenched sample. These results suggest that the Ms and Af are functions not only of the SL21 ; but also of other factors. In fact, the Ms and Af of the sample slowly cooled after annealing at 573 K are 159 and 172 K, respectively, higher than those of the sample annealed at 573 K after quenching. Thermomagnetization M2T curves of cooling and heating of the samples annealed at 473 and 873 K are shown in Fig. 2. The magnetization M curves of the sample annealed at 473 K show two hystereses. The one located at lower temperature corresponds to the martensitic transition. The other one suggests another phase
transition in the austenitic phase. This behavior could not be detected by the DSC measurement. Although the crystal structure does not change in this region, morphology of the magnetic domain dramatically changes according to the TEM observation [12]. This suggests that there is some magnetic phase transition in this region. While the M2T curve of the sample annealed at 873 K showed no abnormal magnetic behavior in the austenite phase, analogous abnormal magnetic behavior was observed in the samples annealed at temperatures lower than 773 K and in the as-quenched sample. In addition, the sample cooled slowly and annealed at 573 K showed no abnormal magnetic behavior. These results suggest that Ms and Af are affected by magnetic factors which would be strongly related to the anti-phase domain boundary structure [12]. In conclusion, the effects of annealing on the martensitic and magnetic transitions of Ni–Ga–Fe FSMA were investigated. Tc of the annealed samples was found to decrease with increasing annealing temperature, and thus the Tc increased with increasing SL21 : The Ms and Af increased with increasing annealing temperature and showed the maxima at annealing temperatures of 873 K. The Ms and Af were affected by not only SL21 ; but also by the magnetic factors. This study was supported by the Industrial Technology Research Grant Program from NEDO, Japan.
References [1] K. Ullakko, J.K. Huang, C. Kanter, V.V. Kokorin, R.C. O’Handley, Appl. Phys. Lett. 69 (1996) 1966. [2] R.D. James, M. Wuttig, Philos. Mag. A 77 (1998) 1273. [3] T. Kakeshita, T. Takeuchi, T. Fukuda, T. Saburi, R. Oshima, S. Muto, K. Kishio, Mater. Trans. JIM 41 (2000) 882. [4] F. Gejima, Y. Sutou, R. Kainuma, K. Ishida, Metall. Mater. Trans. A 30 (1999) 2721. [5] K. Oikawa, L. Wulff, T. Iijima, F. Gejima, T. Ohmori, A. Fujita, K. Fukamichi, R. Kainuma, K. Ishida, Appl. Phys. Lett. 79 (2001) 3290. [6] H. Morito, A. Fujita, K. Fukamichi, R. Kainuma, K. Ishida, K. Oikawa, Appl. Phys. Lett. 81 (2002) 1657. [7] K. Oikawa, T. Ota, Y. Tanaka, T. Omori, R. Kainuma, K. Ishida, Trans. Mater. Res. Soc. Jpn. 28 (2003) 265. [8] K. Oikawa, T. Ota, F. Gejima, T. Ohmori, R. Kainuma, K. Ishida, Mater. Trans. 42 (2001) 2472. [9] K. Oikawa, T. Ota, T. Ohmori, Y. Tanaka, H. Morito, A. Fujita, R. Kainuma, K. Fukamichi, K. Ishida, Appl. Phys. Lett. 81 (2002) 5201. [10] K. Oikawa, T. Ota, Y. Sutou, T. Ohmori, R. Kainuma, K. Ishida, Mater. Trans. 43 (2002) 2360. [11] H. Morito, A. Fujita, K. Fukamichi, R. Kainuma, K. Ishida, K. Oikawa, Mater. Trans. 44 (2003) 661. [12] Y. Murakami, D. Shindo, K. Oikawa, R. Kaiuma, K. Ishida, Appl. Phys. Lett. 82 (2003) 3695.
Journal of Magnetism and Magnetic Materials 272–276 (2004) 2043–2044
Effects of annealing on martensitic and magnetic transitions of Ni–Ga–Fe ferromagnetic shape memory alloys Katsunari Oikawaa,*, Toshihiro Omorib, Ryosuke Kainumab, Kiyohito Ishidab a
National Institute of Advanced Industrial Science and Technology, Tohoku Center, 4-2-1 Nigatake, Miyagino-ku, Sendai 983-8551, Japan b Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
Abstract Effects of annealing on the martensitic and magnetic transitions in Ni51Ga27Fe22 shape memory alloy were investigated. Curie temperature of the annealed sample decreased with increasing annealing temperature, related to degree of the L21 order, SL21 : Both martensitic starting Ms and the austenitic finishing Af temperatures increased with increasing annealing temperature and showed maxima by annealing at 873 K. The Ms and Af seemed to be affected by not only SL21 ; but also by this magnetic behavior. r 2003 Elsevier B.V. All rights reserved. PACS: 78.80.+q; 75.30.Gw; 81.30.Kf Keywords: Ferromagnetic; Shape memory alloy; Martensite; Order–disorder transition; Heusler alloy
Ferromagnetic shape memory alloys (FSMAs) have received much attention due to their potential for use as smart materials, because they show a large magneticfield-induced strain [1]. Several FSMAs have been developed, including Ni2MnGa [1], Fe–Pd [2], Fe–Pt [3], Ni2MnAl [4], and Co–Ni–Al [5,6] systems. Moreover, Ni–Fe–Al [7], Co–Ni–Ga [8] systems have been proposed as the new candidates of FSMAs. Recently, the present authors found promising FSMAs in Ni–Ga– Fe system [9,10]. The Ni–Ga–Fe alloys exhibit a martensitic transformation from a B2 or L21 austenite to a martensite phase with a 7-layer (14 M) or 5-layer (10 M) modulated structure. The principle features of magnetic properties of the 14 M phase in a Ni51:5 Fe22:0 Ga26:5 single crystal have been determined in our previous paper [11]. Recently, it was reported that the austenite phase of Ni–Fe–Ga alloys shows an order–disorder transition from the L21 to the B2 structure at 970 K [9]. It is expected that the magnetic properties and martensitic *Corresponding author. Tel.: +81-22-237-5211; fax: +8122-236-6839. E-mail address: [email protected] (K. Oikawa).
transformation of the ordered alloys significantly depend on the degree of atomic order. In the present study, the effects of annealing temperature on the martensitic and magnetic transitions in a Ni51Ga27Fe22 FSMA were investigated. The alloy ingot was prepared using a cold crucible levitation melting furnace under an argon atmosphere. The small specimens taken from the ingots were homogenized at 1473 K for 3 h and then quenched in ice water. The quenched samples were annealed from 473 to 1023 K for 1 h to promote atomic ordering in the L21 phase and then quenched in ice water. Thermomagnetization curve M2T was measured with a vibrating sample magnetometer at field strength of 500 Oe, and the Curie point Tc was taken as minimum point in the plot of the temperature derivative of magnetization. The martenstitic transition temperatures Ms and Af were determined by differential scanning calorimetry (DSC). Dependence of annealing temperature on the Ms ; Af as well as Tc is shown in Fig. 1. Tc of the annealed samples decreased considerably with increasing annealing temperature in the elevated temperature region over 750 K. According to the TEM observation, the ordered
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.548
ARTICLE IN PRESS K. Oikawa et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 2043–2044
2044 400
Temperature [K]
350 300 250
B2
L21
Tc 200
Ms Af
150 100 as-quench
450
550
650
750
850
950
1050
Annealing temperature [K]
Fig. 1. Annealing temperature dependence of Ms ; Af and Tc :
6 M [arb. unit]
473 K 4 martensitic transition
873 K phase transiton Curie cooling temperature heating
2
0 0
100
200 300 Temperature [K]
400
Fig. 2. Thermomagnetization curve on cooling and heating of the samples annealed at 473 and 873 K.
reflections f1 1 1gL21 in a sample annealed at 773 K were considerably stronger than those in an as-quenched sample, which shows that B2/L21 ordering is promoted by annealing at 773 K. It is clear that the degree of L21 order, SL21 may increase due to annealing at temperatures lower than 773 K, but decrease by annealing at higher temperatures which are close to the B2/L21 ordering temperature of 973 K. Thus, it can be concluded that the increase of Tc is due to the increase of SL21 : On the other hand, both Ms and Af increase with increasing annealing temperature and reach peaks by annealing at 873 K. Further elevating the annealing temperature reduces Ms and Af : From the tendency in the range of 873 to 1023 K, the Ms and Af are expected to increase with increasing SL21 : However, those of the samples annealed at 473 and 573 K were lower than that of the as-quenched sample. These results suggest that the Ms and Af are functions not only of the SL21 ; but also of other factors. In fact, the Ms and Af of the sample slowly cooled after annealing at 573 K are 159 and 172 K, respectively, higher than those of the sample annealed at 573 K after quenching. Thermomagnetization M2T curves of cooling and heating of the samples annealed at 473 and 873 K are shown in Fig. 2. The magnetization M curves of the sample annealed at 473 K show two hystereses. The one located at lower temperature corresponds to the martensitic transition. The other one suggests another phase
transition in the austenitic phase. This behavior could not be detected by the DSC measurement. Although the crystal structure does not change in this region, morphology of the magnetic domain dramatically changes according to the TEM observation [12]. This suggests that there is some magnetic phase transition in this region. While the M2T curve of the sample annealed at 873 K showed no abnormal magnetic behavior in the austenite phase, analogous abnormal magnetic behavior was observed in the samples annealed at temperatures lower than 773 K and in the as-quenched sample. In addition, the sample cooled slowly and annealed at 573 K showed no abnormal magnetic behavior. These results suggest that Ms and Af are affected by magnetic factors which would be strongly related to the anti-phase domain boundary structure [12]. In conclusion, the effects of annealing on the martensitic and magnetic transitions of Ni–Ga–Fe FSMA were investigated. Tc of the annealed samples was found to decrease with increasing annealing temperature, and thus the Tc increased with increasing SL21 : The Ms and Af increased with increasing annealing temperature and showed the maxima at annealing temperatures of 873 K. The Ms and Af were affected by not only SL21 ; but also by the magnetic factors. This study was supported by the Industrial Technology Research Grant Program from NEDO, Japan.
References [1] K. Ullakko, J.K. Huang, C. Kanter, V.V. Kokorin, R.C. O’Handley, Appl. Phys. Lett. 69 (1996) 1966. [2] R.D. James, M. Wuttig, Philos. Mag. A 77 (1998) 1273. [3] T. Kakeshita, T. Takeuchi, T. Fukuda, T. Saburi, R. Oshima, S. Muto, K. Kishio, Mater. Trans. JIM 41 (2000) 882. [4] F. Gejima, Y. Sutou, R. Kainuma, K. Ishida, Metall. Mater. Trans. A 30 (1999) 2721. [5] K. Oikawa, L. Wulff, T. Iijima, F. Gejima, T. Ohmori, A. Fujita, K. Fukamichi, R. Kainuma, K. Ishida, Appl. Phys. Lett. 79 (2001) 3290. [6] H. Morito, A. Fujita, K. Fukamichi, R. Kainuma, K. Ishida, K. Oikawa, Appl. Phys. Lett. 81 (2002) 1657. [7] K. Oikawa, T. Ota, Y. Tanaka, T. Omori, R. Kainuma, K. Ishida, Trans. Mater. Res. Soc. Jpn. 28 (2003) 265. [8] K. Oikawa, T. Ota, F. Gejima, T. Ohmori, R. Kainuma, K. Ishida, Mater. Trans. 42 (2001) 2472. [9] K. Oikawa, T. Ota, T. Ohmori, Y. Tanaka, H. Morito, A. Fujita, R. Kainuma, K. Fukamichi, K. Ishida, Appl. Phys. Lett. 81 (2002) 5201. [10] K. Oikawa, T. Ota, Y. Sutou, T. Ohmori, R. Kainuma, K. Ishida, Mater. Trans. 43 (2002) 2360. [11] H. Morito, A. Fujita, K. Fukamichi, R. Kainuma, K. Ishida, K. Oikawa, Mater. Trans. 44 (2003) 661. [12] Y. Murakami, D. Shindo, K. Oikawa, R. Kaiuma, K. Ishida, Appl. Phys. Lett. 82 (2003) 3695.