Enhanced magnetodielectric response in Dy modified NiCr2O4

The chemically synthesized high purity spinel NiCr2−xDyxO4 (x = 0, 0.1) samples have been characterized using magnetic and dielectric measurements in presence of high magnetic field. Crystal and magnetic structure of the samples have been determined by analyzing neutron diffraction data recorded between temperature of 6 K and 300 K. NiCr2O4 crystallizes in tetragonal phase with the space group of I41/amd whereas NiCr1.9Dy0.1O4 crystallizes in the mixed phase of cubic (space group of Fd3¯m) and tetragonal phases at room temperature. An additional phase of DyCrO3 with orthorhombic structure has been found in the Dy doped compound. The lattice parameter a increases and the c decreases in tetragonal structure with the substitution of Dy in Cr site. Both the samples show superlattice reflection peak indicating the presence of long range AFM ordering (transverse component) below 40 K. But the saturation magnetization slightly increases after Dy doping. An anomaly observed near Curie temperature in ε′ (T) of NiCr2O4 and NiCr1.9Dy0.1O4 demonstrates the contribution of coupling between ferroelectricity and ferrimagnetism in the compounds. A linear correlation between the difference in dielectric constant and the field dependent squared magnetization for both the samples has been observed. The spin-spin interactions are most likely responsible for the observed magnetodielectric (MD) effect due to the magnetodielectric hysteresis in both parent and doped samples. Interestingly the MD% is found to increase with Dy doping.