Temperature dependence of magnetic anisotropy in Co/Pt film on VO₂ with a structural transition

Fifty-nanometer thick (100) and (101) VO₂ films were synthesized on C-plane and R-plane Al₂O₃ substrates using pulsed laser deposition. X-ray diffraction measurements suggested that the VO₂ films with a root-mean-square roughness of 0.58 - 1.08 nm had good crystalline properties. The temperature dependence of the resistance for the VO₂ films displayed a metal-insulator transition behavior at TMI= 325 - 350 K. Co/Pt multilayers with perpendicular magnetic anisotropy were deposited on (100) and (101) VO₂ film by using DC sputtering, and their magnetic properties were monitored by using magneto-optic Kerr effect measurements. Although the VO₂ has a structural transition from monoclinic to tetragonal at the TMI, the (100) VO₂ plane seems to have opposite changes in the two in-plane lattice constants, so no net strain is induced in the neighboring Co/Pt film. On the other hand, the (101) VO₂ with net changes in both in-plane lattice constants at the TMI presumably provides interfacial stress to the neighboring Co/Pt film thus, it induces a net magnetoelastic effect, which results in an increases in the coercive fields of 5 Oe along the easy axis and 200 Oe along the hard axis.