Re-entrant spin glass behaviour and magneto-dielectric effect in insulating Sm2NiMnO6 double perovskite

The structure and magneto-dielectric properties of Sm2NiMnO6 double perovskite have been investigated. The pure monoclinic bulk phase of Sm2NiMnO6 is an intrinsic B-site disordered ferromagnet showing a second order magnetic phase transition similar to 157 K, along with a low temperature re-entrant spin glass-like transition (similar to 20 K) due to the inherent coupling of Ni-Mn network with Sm3+ ion. Moreover, it is an insulator with room temperature dc resistivity similar to 10(8) Omega cm. Furthermore, the high dielectric permittivity (similar to 10(3)) coupled with a shift in dielectric maxima towards higher temperature with frequency, analysis of the phenomenological parameters (T-m, T-B, gamma, Delta T-relax), and the validity of non-linear Vogel-Fulcher relation, we define this ferromagnetic insulator as a relaxor-type dielectric material. Importantly, it exhibits a positive intrinsic magneto-dielectric (MD) response similar to 2% at 100 kHz under a low magnetic field of 0.5 T close to 150 K. The intrinsic MD effect indicates a correlation between spin orientations on the two magnetic sublattices (Ni and Mn) and the magneto-dielectric coupling in the ferromagnetic regime. The insulating ferromagnetic behaviour coupled with MD effect make Sm2NiMnO6 an attractive spintronic material.