The structure and magneto-dielectric properties of Sm 2 NiMnO 6 double perovskite have been investigated.The pure monoclinic bulk phase of Sm 2 NiMnO 6 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 Sm 3+ ion. Moreover, it is an insulator with room temperature dc resistivity $10 8 U cm. Furthermore, the high dielectric permittivity ($10 3 ) coupled with a shift in dielectric maxima towards higher temperature with frequency, analysis of the phenomenological parameters (T m , T B , g, DT 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 Sm 2 NiMnO 6 an attractive spintronic material.

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We present an ab-initio study performed in the framework of density functional theory, group-subgroup symmetry analysis and lattice dynamics, to probe the octahedral distortions, which occur during the structural phase transitions of the quasi-2D layered perovskite Sr3Hf2O7 compound. Such a system is characterized by a high-temperature I4/mmm centrosymmetric structure and a ground-state Cmc21 ferroelectric phase. We have probed potential candidate polymorphs that may form the I4/mmm → Cmc21 transition pathways, namely Fmm2, Ccce, Cmca and Cmcm. We found that the band gap widths increase as the symmetry decreases, with the ground-state structure presenting the largest gap width (∼5.95 eV). By probing the Partial Density of States, we observe a direct relation regarding the tilts and rotations of the oxygen perovskite cages as the transition occurs; these show large variations mostly of the O p-states which contribute mostly to the valence band maximum. Moreover, by analyzing the hyperfine parameters, namely the Electric Field Gradients and asymmetric parameters, we observe variations as the transition occurs, from which it is possible to identify the most plausible intermediate phases. We have also computed the macroscopic polarization and confirm that the Cmc21 phase is ferroelectric with a value of spontaneous polarization of 0.0478 C/m2. The ferroelectricity of the ground-state Cmc21 system arises due to a second order parameter related to the coupling of the rotation and tilts of the O perovskite cages together with the Sr displacements.

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