Collective mode splitting in hybrid heterostructures

We report on a drastic change of the Ni collective magnetization dynamics when incorporated into a $\mathrm{Ni}\text{/}{\mathrm{V}}₂{\mathrm{O}}₃$ heterostructure. Two, unexpected, well-defined Ni ferromagnetic resonance (FMR) modes are observed in the coexistence region of the first-order ${\mathrm{V}}₂{\mathrm{O}}₃$ structural phase transition (SPT). The phase coexistence across the ${\mathrm{V}}₂{\mathrm{O}}₃$ SPT can explain the presence of the two resonance fields but not their anticrossing and large linewidth broadenings. Our results imply a strong coupling between the lattice dynamics of the strongly correlated oxide (${\mathrm{V}}₂{\mathrm{O}}₃$) and the magnon modes of the ferromagnet (Ni) in this hybrid. This and additional experiments on Ni grown on $\mathrm{SrTi}{\mathrm{O}}₃$, a prototypical second-order phase transition oxide, imply that these effects require the presence of first-order transitions in the oxides.