Correlation Between Elastic Constants and Magnetic Anisotropy in Co/Pt Superlattice Thin Films
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Correlation Between Elastic Constants and Magnetic Anisotropy in Co/Pt Superlattice Thin Films Nobutomo Nakamura1, Hirotsugu Ogi1, Teruo Ono2, Masahiko Hirao1, Takeshi Yasui1, and Osamu Matsuda3 1 Graduate School of Engineering Science, Osaka University, Machikaneyama 1-3, Toyonaka, Osaka 560-8531, Japan. 2 Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan. 3 Faculty of Engineering, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo 060-8628, Japan. ABSTRACT In this paper, we study contribution of the magnetoelastic anisotropy effect on perpendicular magnetic anisotropy of Co/Pt superlattice thin films. The effective-magnetic anisotropy energy was measured for Co/Pt thin films with a constant Co-layer thickness (4 Å) deposited on silicon substrate by the ultrahigh-vacuum deposition method. As the Pt-layer thickness increases, the effective-magnetic anisotropy energy increases and decreases after showing a maximum at the Pt-layer thickness of 12 Å. This behavior can be explained only by the magnetoelastic anisotropy effect, that is, elastic-strain energy released through the magnetostriction effect with the strain-dependent elastic constants. INTRODUCTION Magnetization direction of a ferromagnetic thin film is usually parallel to the film surface because of strong contribution of the magnetic shape-anisotropy effect. However, it can be perpendicular to the film surface for such a system that consists of magnetic-material/noble-metal multilayer thin film, when the thickness of the magnetic-material layer is of the order of a few angstroms. This magnetic property is called perpendicular magnetic anisotropy (PMA) [1,2]. PMA will appear when the total energy of the system takes a minimum with the perpendicular magnetization. The total energy of the system consists of magnetocrystalline anisotropy energy, magnetic shape-anisotropy energy, magnetic interfacial-anisotropy energy, and magnetoelastic anisotropy energy. Considering the magnetocrystalline anisotropy and magnetic shape-anisotropy energies, the magnetization direction of a thin film of Co always lies in the film plane. However, the magnetization direction of Co/Pt superlattice thin films can be perpendicular to the film surface because of the
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magnetic interfacial-anisotropy energy and magnetoelastic anisotropy energy. PMA can be candidates for ultrahigh-density-magnetic-recording media, and clarification of its mechanism is a long running problem. For deep understating of the cause of PMA in the Co/Pt system, previous works studied dependence of PMA on the Co-layer thickness [1-5]. However, changing the Co-layer thickness affects both the magnetic interfacial and magnetoelastic anisotropy energies per unit volume of Co, and their contributions to PMA cannot be separately evaluated. In this paper, we study contribution of the magnetoelastic anisotropy energy to PMA by measuring PMA with various Pt-layer thickness, remaining the Co-layer thickness unchanged, where only the magnetoelastic anisotropy energy
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