Exploring the structural, magnetic, and dielectric properties of Fe and Y substituted NiCr2O4

This paper presents the successful single phase synthesis of NiCr2O4 and NiFe0.50Cr1.50-xYxO4 (x = 0 - 0.08) compounds followed by an investigation into their structural, magnetic and dielectric properties. The structural analysis confirms tetragonal structure for NiCr2O4 while a partially inverse cubic spinel structure for Fe and Y substituted samples (x = 0 - 0.08). Fe substitution (x = 0) induces a shift in room temperature hysteresis loop behaviour from paramagnetic to ferrimagnetic, suggesting enhanced superexchange interactions and a significant rise in magnetic transition temperature beyond room temperature. However, it is found that further inclusion of Y (x = 0.04 - 0.08) leads to a slight weakening of superexchange interactions. The saturation magnetization increases with Y substitution, while coercivity and magnetocrystalline anisotropy follows a decreasing trend. The complex impedance studies unveil a relaxation phenomenon and the dielectric constant is found to increase with the substitution of Fe and Y. Analysis of temperature dependent ac conductivity data and the frequency exponent profile suggests small polaron hopping as the predominant transport mechanism up to 380 K in NiCr2O4 and x = 0 samples, shifting to large polaron hopping beyond this temperature. In samples with x =0.04 and 0.06 the transport mechanism is found to follow the small polaron tunneling model. However, in the x = 0.08 sample, large polaron tunneling becomes predominant beyond 365 K.