Origin of magnetization-induced anisotropy of magnetic films

It is proposed that the magnetization-induced anisotropy of magneticfilms of cubic crystal structure originates from the anisotropy ofatomic pair ordering, shape anisotropy, and strain anisotropyresulting from the constraint of the magnetostriction strain imposedon the film by the substrate. Calculated are the three anisotropyconstants and their sum $K $ vs temperature for Ni, Fe, and55%Ni--Fe films; the room temperature (RT) constants vs thesubstrate temperature $T_{\rm t}$ during deposition or annealingafter deposition for Ni and 50%Ni--Co films; the RT constants vscomposition 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$^\circ$Cand 320$^\circ$C, and Fe--Co films with $T_{\rm t}=$ RT and 300$^\circ$C;the spread of RT $K$ vs compositionfraction for Fe--Ni films; and RT $\Delta K/K$ vs compositionfraction for Fe--Ni and Co--Ni films, where $\Delta K$ denotes thevariation of $K$ of the film that is detached from its substrate. Thecalculated curves well accord with the measurements. The irrelevancyof $K$ to the substrate material and the fast kinetics of theannealing in a field applied in the direction of the hard axis areexplained reasonably.The anisotropies of Fe and Ni films originate mainly from the shapeanisotropy and the strain anisotropy, respectively. The majoranisotropy component in many cases depends not only on compositionfraction but also on $T_{\rm t}$ . For example, the RT anisotropy of40$- $70%Ni--Fe films, when $T_{\rm t}$ is RT, mostly comes fromthe anisotropy of atomic pair ordering while it stems mostly from theshape anisotropy when $T_{\rm t}$is 450$^\circ$C.The most important cause of the spread in values of $K$ is the spread of theintrinsic anisotropic stresses superimposed on the intrinsic isotropicplanar stress. It is suggested that the field cooling induced magneticanisotropy originating from the induced crystal texture observed in the bulkalloys is also a major origin for Co and Co-rich alloy films of hexagonalcrystal structure.