EXOTIC THIN FILMS MADE FROM COBALT FERRITE

摘要

Epitaxial CoFe_2O_4 thin films have been grown by PLD on (100) MgO substrate. Two types of spin-reorientation have been observed in such films upon annealing or increasing the film-thickness. In the as-deposited layers and at low thickness the easy axis is confined to the normal to the film plane whereas at large thickness the film plane becomes the preferential direction of the magnetization. On the other hand annealing induces a reorientation of magnetic anisotropy, which switches from the normal to the film plane in the as-deposited film to be in-plane aligned in the annealed state. The origin of both reorientations is explained in term of competition between stress and magnetocrystalline anisotropies. In the as-deposited state the tensile stress induces a huge perpendicular anisotropy, dominating the in-plane magnetocrystalline component. However annealing or increasing the film thickness releases the stress and allows the in-plane magnetocrystalline anisotropy to take the lead.