Magneto-dielectric effect in relaxor superparaelectric Tb2CoMnO6 film

We report magneto-dielectric properties of partially B-site ordered monoclinic ${\mathrm{Tb}}₂\mathrm{CoMn}{\mathrm{O}}₆$ double perovskite thin film epitaxially grown on $\mathrm{Nb}:\mathrm{SrTi}{\mathrm{O}}₃$(100) substrates by metalorganic aerosol deposition technique. Transmission electron microscopy and electron energy loss spectroscopy mapping shows the presence and distribution of both $\mathrm{C}{\mathrm{o}}²⁺$ and $\mathrm{C}{\mathrm{o}}³⁺$ ions in the film, evidencing a partial $B$-site disorder, which was further confirmed by the observation of reduced saturation magnetization at low temperatures. The ferromagnetic Curie temperature, ${T}_C=110\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, is slightly higher as compared to the bulk value (100 K) probably due to an in plane epitaxy tensile strain. Temperature dependent dielectric study reveals an unexpected high temperature dipolar relaxor-glass-like transition at a temperature ${T}^*\ensuremath{\sim}190\phantom{\rule{0.16em}{0ex}}\mathrm{K}>{T}_{\mathrm{C}}$, which depends on the applied frequency and indicates a superparaelectric behavior. Two different dielectric relaxation peaks have been observed; they merge at ${T}^*$ where likely a coupling to the disorder-induced short range charge-spin correlations results in a 4% magneto-dielectric coupling.