Institute for Materials Research (IMR), Tohoku University, Japan
Abstract:
1. Introduction
Large uniaxial magnetic anisotropy materials are extremely promising for the application to rare-earth-free permanent magnets. As one of the materials, L10-ordered FeNi alloy is attracting attention because it reveals large Ku (uniaxial magnetic anisotropy energy) value in bulk[1]. However, it is difficult to obtain the L10 phase by conventional techniques because the order-disorder transformation temperature of L10-FeNi is low (320 ˚C). In this study, we successfully obtained L10-FeNi thin films with a large Ku by alternate monatomic layer deposition using MBE (molecular beam epitaxy)[2-7]. FeNi films including L10 phase were also fabricated by sputtering and post-annealing. Structural and magnetic properties were systematically investigated for FeNi thin films, and clarified the origin of the large magnetic anisotropy in L10-FeNi.
Large uniaxial magnetic anisotropy materials are extremely promising for the application to rare-earth-free permanent magnets. As one of the materials, L10-ordered FeNi alloy is attracting attention because it reveals large Ku (uniaxial magnetic anisotropy energy) value in bulk[1]. However, it is difficult to obtain the L10 phase by conventional techniques because the order-disorder transformation temperature of L10-FeNi is low (320 ˚C). In this study, we successfully obtained L10-FeNi thin films with a large Ku by alternate monatomic layer deposition using MBE (molecular beam epitaxy)[2-7]. FeNi films including L10 phase were also fabricated by sputtering and post-annealing. Structural and magnetic properties were systematically investigated for FeNi thin films, and clarified the origin of the large magnetic anisotropy in L10-FeNi.
2. Experimental
FeNi films were fabricated by MBE employing an alternative monatomic deposition of Fe and Ni layers on several underlayers. They were fabricated also by sputtering on a MgO(001) substrate and subsequent rapid thermal annealing (RTA). Structural properties were investigated by X-ray diffraction (XRD) using synchrotron radiation and transmission electron microscope observation. Magnetic properties were characterized by a superconducting quantum interference device.
FeNi films were fabricated by MBE employing an alternative monatomic deposition of Fe and Ni layers on several underlayers. They were fabricated also by sputtering on a MgO(001) substrate and subsequent rapid thermal annealing (RTA). Structural properties were investigated by X-ray diffraction (XRD) using synchrotron radiation and transmission electron microscope observation. Magnetic properties were characterized by a superconducting quantum interference device.
3. Results and Discussion
Ku of FeNi this film fabricated by MBE was evaluated to be about 0.7 MJ/m3 from the magnetization curves, and it is confirmed that large magnetic anisotropy is induced by the formation of L10 type structure. The relationship between Ku and chemical order parameter (S), which was estimated from XRD measuremets, was investigated. Ku was roughly proportional to S, indicating clear correlation between Ku and S. On the other hand, XRD patterns of FeNi films fabricated by sputtering drastically changed depending on the condition of RTA. Magnetization curves also changed with the annealing temperature and the annealing time, which implied the successful formation of L10-FeNi. In addition, the enhancement of coercivity and remanent magnetization was observed associated with the appearance of L10 phase.
Ku of FeNi this film fabricated by MBE was evaluated to be about 0.7 MJ/m3 from the magnetization curves, and it is confirmed that large magnetic anisotropy is induced by the formation of L10 type structure. The relationship between Ku and chemical order parameter (S), which was estimated from XRD measuremets, was investigated. Ku was roughly proportional to S, indicating clear correlation between Ku and S. On the other hand, XRD patterns of FeNi films fabricated by sputtering drastically changed depending on the condition of RTA. Magnetization curves also changed with the annealing temperature and the annealing time, which implied the successful formation of L10-FeNi. In addition, the enhancement of coercivity and remanent magnetization was observed associated with the appearance of L10 phase.
References
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[2] T. Shima et al., J. Magn. Magn. Mater. 310 (2007) 2213.
[3] M. Mizuguchi et al., J. Appl. Phys. 107 (2010) 09A716.
[4] M. Mizuguchi et al., J. Magn. Soc. Jpn. 35 (2011) 370.
[5] T. Kojima et al., Jpn. J. Appl. Phys. 51 (2012) 010204.
[6] T. Kojima et al., J. Phys.: Conden. Matter 26 (2014) 064207.
[7] T. Kojima et al., J. Phys. D: Appl. Phys. 47 (2014) 425001.
[1] J. Paulevé et al., J. Appl. Phys. 39 (1986) 989.
[2] T. Shima et al., J. Magn. Magn. Mater. 310 (2007) 2213.
[3] M. Mizuguchi et al., J. Appl. Phys. 107 (2010) 09A716.
[4] M. Mizuguchi et al., J. Magn. Soc. Jpn. 35 (2011) 370.
[5] T. Kojima et al., Jpn. J. Appl. Phys. 51 (2012) 010204.
[6] T. Kojima et al., J. Phys.: Conden. Matter 26 (2014) 064207.
[7] T. Kojima et al., J. Phys. D: Appl. Phys. 47 (2014) 425001.