Influence of Intermediate Ag Layer Thickness on Phase Transformations in FePt/Ag/FePt Thin Film Compositions

Abstract

Background. Film compositions with chemically ordered and magnetically hard L 1 0 - FePt phase are the perspective materials for ultrahigh density magnetic recording. The deposition on heated substrate or providing an annealing is required for L 1 0 - FePt phase formation. However, heat treatment causes the grains growth and increase of surface roughness of the films, which complicates the practical use of these materials. The introduction of intermediate layers of “third” elements between FePt alloy layers is one of the possible solutions of this problem, which can reduce the temperature of А 1‑FePt ® L 1 0 ‑FePt phase transformation. Objective. Investigation of the influence of intermediate Ag layer thickness on the structure and magnetic properties of FePt/Ag(7.5; 30 nm)/FePt compositions. Methods. Film compositions were obtained by magnetron sputtering, structure and properties before and after heat treatment were investigated by X-ray diffraction, atomic force microscopy, magnetometry and resistometry. Results. It is determined that increasing of Ag layer thickness from 7.5 nm up to 30 nm leads to a reduction of the L 1 0 - FePt phase formation temperature for ~ 100 K and to an increase of the compositions coercivity. Conclusions. A possible explanation for the phenomenon of L 1 0 - FePt phase formation temperature reduction with increasing Ag intermediate layer thickness lies in the difference between the stress states that occur in these films during annealing due to differences in linear expansion coefficients of their layers. The thickness increase of the intermediate Ag layer increases the composition coercivity as a result of saturation of the grain boundaries of the L 1 0 -FePt phase with non-magnetic ingredient and limitation of the exchange interaction between the grains.