Increase in Coercive Field by Magnetoelastic Coupling in Co/VO₂ Films

Abstract

Herein, a ferromagnetic cobalt (Co) film was deposited on a VO₂ film exhibiting a structural phase transition from monoclinic to tetragonal at ~340 K to investigate the magnetoelastic effect caused by a phase-transition-induced strain. First, (100) and (101) VO₂ films with thicknesses of 11-43 nm were grown on Al₂O₃ using pulsed laser deposition, and 2.5-nm-thick Co films were deposited on top of them via sputtering. The magneto-optic Kerr effect hysteresis loops were measured with the temperature variation across the structural phase transition temperature of VO₂. Upon heating, an increase in the coercive field of the Co layer was observed at the structural phase transition temperature of VO₂, suggesting a magnetoelastic coupling between the Co and VO₂ layers. The coercive field increment diminished with decreasing VO₂ thickness, and it disappeared as the VO₂ became thinner than a critical value of ~11 nm. These results imply that a phase-transition-induced strain in the VO₂ layer can be used to change the coercive field of the neighboring magnetic layer.