Origin of magnetization-induced anisotropy of magnetic films
Jin Han-Min(金汉民)a)b)†, Chong-Oh Kima), Taek-Dong Leec), and Hyo-Jin Kimd)
a Research Center for Advanced Magnetic Materials, Chungnam National University, 220, Gung-dong, Youseong-gu, Daejeon 305- 64, RO Korea; b Department of Physics, Jilin University, Changchun 130023, China; c Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1, Kusong-dong, Youseong-gu, Daejeon 305-704, RO Korea; d Department of Materials Science and Engineering, Chungnam National University, 220, Gung-dong, Youseong-gu, Daejeon 305-764, RO Korea
AbstractIt is proposed that the magnetization-induced anisotropy of magnetic films of cubic crystal structure originates from the anisotropy of atomic pair ordering, shape anisotropy, and strain anisotropy resulting from the constraint of the magnetostriction strain imposed on the film by the substrate. Calculated are the three anisotropy constants and their sum $K $ vs temperature for Ni, Fe, and 55%Ni--Fe films; the room temperature (RT) constants vs the substrate temperature $T_{\rm t}$ during deposition or annealing after deposition for Ni and 50%Ni--Co films; the RT constants vs composition fraction for Fe--Ni films with $T_{\rm t}=$ RT, 250$^\circ$C and 450$^\circ$C, Co--Ni films at $T_{\rm t} =$ RT, 100$^\circ$C and 320$^\circ$C, and Fe--Co films with $T_{\rm t}=$ RT and 300$^\circ$C; the spread of RT $K$ vs composition fraction for Fe--Ni films; and RT $\Delta K/K$ vs composition fraction for Fe--Ni and Co--Ni films, where $\Delta K$ denotes the variation of $K$ of the film that is detached from its substrate. The calculated curves well accord with the measurements. The irrelevancy of $K$ to the substrate material and the fast kinetics of the annealing in a field applied in the direction of the hard axis are explained reasonably. The anisotropies of Fe and Ni films originate mainly from the shape anisotropy and the strain anisotropy, respectively. The major anisotropy component in many cases depends not only on composition fraction but also on $T_{\rm t}$ . For example, the RT anisotropy of 40$- $70%Ni--Fe films, when $T_{\rm t}$ is RT, mostly comes from the anisotropy of atomic pair ordering while it stems mostly from the shape anisotropy when $T_{\rm t}$ is 450$^\circ$C. The most important cause of the spread in values of $K$ is the spread of the intrinsic anisotropic stresses superimposed on the intrinsic isotropic planar stress. It is suggested that the field cooling induced magnetic anisotropy originating from the induced crystal texture observed in the bulk alloys is also a major origin for Co and Co-rich alloy films of hexagonal crystal structure.
Accepted manuscript online:
PACS:
75.70.Ak
(Magnetic properties of monolayers and thin films)
Jin Han-Min(金汉民), Chong-Oh Kim, Taek-Dong Lee, and Hyo-Jin Kim Origin of magnetization-induced anisotropy of magnetic films 2007 Chinese Physics 16 3520
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