Mechanism of c-axis orientation of L1(0) FePt in nanostructured FePt/B2O3 thin films

摘要

In oder to obtain a high-density magnetic recording medium using an L10 ferromagnetic ordered alloy, it is imperative to make its c-axis perpendicular to the thin film. In this work, we have investigated experimentally the c-axis orientation process of the L10 FePt in nanostructured FePt/B2O3 thin films, and its orientation mechanism is proposed on the basis of the micromechanics concept. From our present experimental results, we have found that there are three characteristic features when such c-axis orientation occurs in the thin films: the marked crystallographic orientation occurs during the cooling process, the axial ratio c/a experimentally observed tends to be considerably lower than the equilibrium value, and the degree of c-axis orientation is lowered for a relatively thick film, that is, the plane-stress state plays a key role to make the c-axis perpendicular to the film surface. In-plane (biaxial) tensile stresses are considered to be yielded due to the thermal shrinking difference between the two materials, and ordered FePt particles with the c-axis perpendicular to the film surface is considerably stabilized under such in-plane tensile stresses in terms of the mechanical interaction energy. The validity of this mechanism is also confirmed for CoPt/B2O3 thin films.