Exploring the influence of Bi-substitution in La2NiMnO6: Structural distortion, spin-glass, and magnetodielectric effect

Bi-substituted La_1.5Bi_0.5NiMnO₆ polycrystals were synthesized using sol-gel method to investigate the structural and magnetic frustration. XRD data refinement confirmed a phase co-existence of disordered rhombohedral and ordered monoclinic structures, indicative of enhanced structural distortion. It exhibits site disorder and a second-order magnetic phase transition at T_C ∼181 K, along with low-temperature glassy behaviour, driven by the mixed valence states of Ni^2+/3+ and Mn^4+/3+. Bi doping leads to a reduction in T_C and magnetization due to the anti-site disorder. Magnetic memory and AC susceptibility studies confirm the spin-glass and cluster-glass dynamics at freezing temperatures of T_f1 ∼115 K and T_f2 ∼33 K, respectively. Temperature dependent electrical resistivity governs the variable-range hopping mechanism and exhibits negative magnetoresistance. Frequency-dependent dielectric studies reveal a magnetodielectric response of 8 % near T_C. Systematic study of H-dependent impedance and resistivity divulged that a dominant extrinsic contribution from the Maxwell-Wagner coupled with magnetoresistance property contributes to magnetodielectric effect.