Solid-state synthesis, rotatable magnetic anisotropy and characterization of Co1-xPtx phases in 50Pt/50fccCo(001) and 32Pt/68fccCo(001) thin films

We reported the phase formation sequences in 50Pt/50fcc-Co(001) and 32Pt/68fcc-Co(001) thin films after annealing up to 850 degrees C. In both cases, the ordered L1(0 )phase formed first on the Pt/Co interface at similar to 400 degrees C and as the annealing temperature increased the L1(0) phase transformed into the chemically disordered fcc Al phase in 50Pt/50fcc-Co(001) at 750 degrees C and in 32Pt/68fcc-Co(001) films at 550 degrees C. Based on the analysis of solid-state reactions in thin films, a phase transition at similar to 400 degrees C is predicted in Co-Pt systems with a 32-72% Pt composition. Torque measurements of the 50Pt/50fcc-Co(001) samples showed that the rotatable magnetic anisotropy coexisted with the three variants of L1(0) in a temperature range of 400-750 degrees C. An analysis of the torque curves revealed that the L1(0) films consist of a soft magnetic layer epitaxially intergrown to the substrate MgO(001) and a top layer having rotatable magnetic anisotropy. It showed that the magnetically hard properties of L1(0) films are associated with a rotatable magnetic anisotropy layer. A model of rotatable magnetic anisotropy is reasoned, which is founded on some identical mechanisms of rotatable magnetic anisotropy and magnetic-field-induced strains, explaining the ferromagnetic shape-memory effect in Heusler alloys. Our results suggested that the rotatable magnetic anisotropy phenomena may have an important role in the origin of perpendicular anisotropy in hard magnetic L1(0) structures. (C) 2020 Elsevier B.V. All rights reserved.