Study of strain-mediated couplings in SrRuO$_3$-CoFe$_2$O$_4$ nanocomposite by Raman spectroscopy

Self-assembled vertical nanostructures have the advantage of high interface-to-volume ratio and can be used to generate new functionalities by the choice of combination of constituents. Recently, we found an interesting behavior of photo-induced magnetization switching in a self-assembled system, CoFe$_2$O$_4$ (CFO) nanopillars embedded in SrRuO$_3$(SRO) matrix. In this study, to further reveal the coupling mechanism of this hetero-structure, we used Raman spectroscopy to investigate their phonons under external stimulus. When an external out-of-plane magnetic field is applied, the CFO A1g phonon (688 cm$^{-1}$) had a red shift due to the negative magnetostriction effect, while the SRO Ag phonon (183 cm$^{-1}$) also had a correspondent red shift. This result indicates the crystal structures of SRO matrix are affected by the deformation of the CFO pillars through the magnetostrictive couplings. Moreover, at the phase transition temperature of SRO (160 K), three phonons (T$_{2u}$, E$_g$, E$_u$) of CFO also had a significant blue shift, which reveals again the strain-mediated coupling.