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

Abstract

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 ∼157 K, along with a low temperature re-entrant spin glass-like transition (∼20 K) due to the inherent coupling of Ni–Mn network with Sm³⁺ ion. Moreover, it is an insulator with room temperature dc resistivity ∼10⁸ Ω cm. Furthermore, the high dielectric permittivity (∼10³) coupled with a shift in dielectric maxima towards higher temperature with frequency, analysis of the phenomenological parameters (T_m, T_B, γ, ΔT_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 ∼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.