Effective control of the magnetic anisotropy in ferromagnetic MnBi micro-islands

This work shows the possibility of tailoring the magnetic anisotropy direction in ferromagnetic LTP-MnBi thin films from out-of-plane to in-plane while also making possible for the first time the growth of quasi-hexagonal LTP-MnBi micro-islands. This has been managed with no need to apply any external magnetic field, but only by controlling the temperature growth. The rf sputtering of a Mn–Bi composite target produces highly crystalline <002> oriented micro-islands with a size distribution in the micrometer range (up to 80 μm) for samples grown at 300–425 K and <110> oriented elongated threads at 475 K. The <002> oriented films show perpendicular magnetic anisotropy while the <110> oriented ones show in-plane anisotropy. High values of coercivity have been obtained, reaching maximum values of 16.0 and 19.3 kOe at 300 and 400 K, respectively, for these LTP-MnBi thin films. Micromagnetic simulations have shown a clear correlation between the microstructure and the resulting magnetic properties. The route presented here represents a first step towards the possible fabrication of MnBi thin film micromagnets with customized magnetic anisotropy direction based on the deposition temperature.