Magnetic anisotropy of polycrystalline high-temperature ferromagnetic MnxSi1-x (x≈0.5) alloy films

A set of thin film MnxSi1-x alloy samples with different manganese concentration x≈0.44−0.63 grown by the pulsed laser deposition (PLD) method onto the Al2O3 (0001) substrate was investigated in the temperature range 4–300K using ferromagnetic resonance (FMR) measurements in the wide range of frequencies (f=7−60GHz) and magnetic fields (H=0−30kOe). For samples with x≈0.52−0.55, FMR data show clear evidence of ferromagnetism with high Curie temperatures TC∼300K. These samples demonstrate a complex magnetic anisotropy described phenomenologically as a combination of the essential second order easy plane anisotropy contribution and the additional fourth order uniaxial anisotropy contribution with easy direction normal to the film plane. The observed anisotropy is attributed to a polycrystalline (mosaic) structure of the films caused by the film-substrate lattice mismatch. The existence of extra strains at the crystallite boundaries initiates a random distribution of local in-plane anisotropy axes in the samples. As a result, the symmetry of the net magnetic anisotropy is axial with the symmetry axis normal to the film plane. The principal features of the observed anisotropy are explained qualitatively within the proposed microscopic model.