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

Herein, a ferromagnetic cobalt (Co) film was deposited on a VO2 film exhibiting a structural phase transition from monoclinic to tetragonal at similar to 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 similar to 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.