Temperature Dependence of the Coercivity of VO$_{\mathrm{2}}$/Ni Bilayers

The temperature dependence of the coercivity and magnetization of VO$_{\mathrm{2}}$/Ni bilayers was studied. VO$_{\mathrm{2}}$ exhibits a well-known Structural Phase Transition (SPT) at 330-340 K, from a low temperature monoclinic (M) to a high temperature rutile (R) structure. VO$_{\mathrm{2}}$/Ni bilayers were grown using a magnetron sputtering technique onto different substrates. The magnetic properties were measured using a Vibrating Sample Magnetometer. The SPT of VO$_{\mathrm{2}}$ induces an inverse magnetoelastic effect that strongly modifies the coercivity and magnetization of the Ni films. In addition, the growth conditions allow tuning of the magnetic properties. Ni films deposited in the rutile phase on top of VO$_{\mathrm{2}}$ (M) show an irreversible change in the coercivity after the first cycle through the high temperature phase, with a corresponding change in the surface morphology. On the other hand, the Ni films grown on top of VO$_{\mathrm{2}}$ (R) do not show this irreversibility. These results indicate that: i) magnetic properties of magnetic films are strongly affected by the strain induced by materials that undergo a structural phase transition; and ii) it is possible to control the properties by tuning the growth conditions.