Strain control of Morin temperature in epitaxial α-Fe2O3(0001) film

We present comprehensive studies of strain effects on the spin reorientation transition (SRT), the so-called Morin transition, in alpha-Fe2O3(0001) films. The alpha-Fe2O3(0001) epitaxial films were grown with a Cr2O3 buffer layer on Al2O3(0001) substrates through an oxide molecular beam epitaxy. The antiferromagnetic spin axis was monitored by using the Fe L-2-edge X-ray magnetic linear dichroism. The buffer layer was found to introduce compressive strain into the alpha-Fe2O3(0001) film due to its 1.6% smaller in-plane lattice constant. The degree of strain is monotonically reduced with the increase of the alpha-Fe2O3 film thickness and becomes relaxed in the thick region (>20 nm). The transition temperature T-M, which increases up to similar or equal to 360K, well above the bulk T-M = 263 K, for the film thickness similar or equal to 3 nm, gradually decreases as the film thickness increases. We also examined the Neel temperature T-N in the ultra-thin region (<3nm), which rapidly drops with the decrease of the film thickness. The correlation between T-M and the strain in the alpha-Fe2O3(0001) epitaxial films was found to be well explained in terms of two competing energies of magnetic dipole anisotropy and single-ion magnetocrystalline anisotropy except for the ultra-thin region, in which TN is dominated by the finite-size effects. Copyright (C) EPLA, 2013