Angular-dependent magnetic properties in V2O3/Ni hybrid heterostructures

In this paper, we investigate the in-plane angular and temperature dependence of coercivity and exchange bias in a ${\mathrm{V}}_{2}{\mathrm{O}}_{3}/\mathrm{Ni}$ magnetic bilayer structure, grown on an $r$-plane sapphire ($\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$) substrate using reactive dc-magnetron sputtering. Distinct variations are observed in coercivity and exchange field across the structural phase transition in ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$, depending on in-plane angles and different field cooling states, as well as the direction of the applied cooling field. A peak in coercivity, occurring at a temperature corresponding to the phase coexistence region of the ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ structural transition, is observed only along the primary easy axis (${0}^{\ensuremath{\circ}}/{180}^{\ensuremath{\circ}}$) of the film, disappearing at other angles and remaining independent of the field cooling state. Temperature-dependent measurements, with the applied cooling field along different angles, revealed that the onset of exchange bias at the structural phase transition of the ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ occurs irrespective of the cooling field state, yet demonstrates a complex in-plane angular dependence based on the orientation of the applied cooling field. The cooling field orientation influences the exchange bias's anisotropy, magnitude, and direction; notably, a typical unidirectional symmetry emerges when the cooling field aligns with the secondary easy axis (${90}^{\ensuremath{\circ}}/{270}^{\ensuremath{\circ}}$) of the film, which nearly aligns with vanadium magnetic moments.