Epitaxial τ phase MnAl thin films on MgO (001) with thickness-dependent magnetic anisotropy

In this study, ferromagnetic MnAl films were prepared by alternating Al/Mn quasi-monolayer deposition using a novel biased target ion beam deposition (BTIBD) technique. XRD results showed that the magnetic tau phase was well formed in MnAl thin films (similar to 10 nm), which grew epitaxially on single crystal MgO (001) substrates. The optimized saturation magnetization was similar to 394 emu/cc. Furthermore, we observed a thickness-dependent uniaxial anisotropy in ferromagnetic MnAl films, which was attributed to the change of the tetragonal lattice distortion as a function of film thickness. The relationship between the film thicknesses and saturation magnetizations suggested the existence of a magnetically dead layer similar to 2.7 nm with an extrapolated saturation moment around 523 emu/cc (similar to 1.90 mu B/Mn). This value has exceeded the experimental value in bulk materials and is close to the theoretically predicted magnetization (similar to 1.975 mu B/Mn). VC 2011 American Institute of Physics. [doi:10.1063/1.3663435]