Magnetism of CoFe_2O_4 ultrathin films on MgAl_2O_4 driven by epitaxial strain

摘要

We report on the correlations between magnetic anisotropy and strain state in CoFe_2O_4 ultrathin films grown on MgAl_2O_4(100) and MgAl_2O_4(111) substrates. By local strain analysis using the geometric phase method, a significant in-plane compressive strain is observed for the (001) orientation while a full relaxation is detected for the (111) orientation. The relaxation process in CoFe_2O_4( 111) layers induces interface dislocations and a large amount of antiphase boundaries while a pseudomorphic growth is observed for the (001) direction, decreasing significantly the density of antiphase boundaries. By comparing the magnetoelastic energy terms, the correlation between strain state and resultant magnetization is discussed.