Magnetic phase diagram and dielectric properties of Mn doped CoCr2O4 nanoparticles

Abstract

Abstract Effects of Manganese (Mn) substitution on the magnetic and dielectric properties of spinel phase Co1−xMnxCr2O4 (0.0 ≤ x ≤ 1) nanoparticles (NPs) have been studied. X-ray diffraction and Fourier transform infrared spectroscopy analysis showed the normal spinel structure for all the samples. Average crystallite size showed increasing trend with Mn doping and lies in the range 32–47 nm. The undoped CoCr2O4 NPs displayed a typical phase transition from paramagnetic (PM) to ferrimagnetic (FiM) state at TC = 100 K along with conical spiral magnetic state at TS = 27 K and lock-in transition state at TL = 13 K. The TC, TS and TL values were shifted towards lower temperatures with increasing Mn content and finally an antiferromagnetism (AFM) is obtained for MnCr2O4 NPs at TN = 20 K. A magnetic phase diagram was developed which showed the presence of different phases in these nanoparticles and attributed it to change in magnetic interactions with increasing Mn content. Saturation magnetization (MS) showed an increasing trend with Mn content due to the large magnetic moment of Mn ions. Nanoparticles showed an overall increasing trend of the dielectric constant with Mn concentration which is due to possible hopping of Mn2+ to Mn3+ and as well as increasing average crystallite size with Mn doping. In summary, increase in Mn doping revealed reduction in TC, TS, and TL values, an increasing MS trend, an AFM phase introduction and improved dielectric properties for Co1−xMnxCr2O4 NPs.