Magnetization states in epitaxial thin films subjected to misfit strains and demagnetization field

The effect of non-equally biaxial in-plane misfit strains and demagnetization field on the magnetization states of ferromagnetic thin films is analytically investigated by using a nonlinear thermodynamic theory. The “misfit strain–misfit strain” phase diagrams of the magnetization states at room temperature for α-Fe and CoFe2O4 thin films epitaxially grown on tetragonal substrates are developed by minimizing the total free energy. For a cubic ferromagnetic thin film, an out-of-plane magnetization state exists in the region of tensile misfit strains if the magnetostrictive coefficient of λ100 is negative and the demagnetization field is small, whereas the out-of-plane magnetization vanishes in the whole region of misfit strains when the demagnetization field is large.