Magnetic field dependence of magnetic coupling in CoCr2O4 nanoparticles

Abstract

CoCr2O4 spinel nanoparticles synthesized by sol-gel method have been worked extensively by performing structural and magnetic characterization techniques, as well as modeling the experimental results. The microstructure analysis shows that the crystallite size of CoCr2O4 nanoparticles, which are purely crystallized in cubic phase with space group Fd3m, is similar to 75 nm. The grain size distribution determined from scanning electron microscope images indicates that the particles are uniformly formed and distributed homogenously in the structure. A comprehensive magnetic study has been performed by measuring magnetic moment as a function of temperature and external magnetic field. The paramagnetic to ferromagnetic phase transition and non-collinear spiral magnetic transition have been observed in CoCr2O4 nanoparticles at 96 and 27 K, respectively. Interestingly, we observed field-condition shift in lock-in transition which is found as 16 and 8 K for FH and FC, respectively. The exchange bias effect is observed when the CoCr2O4 sample is cooled under magnetic field. The magnitude of exchange bias field decreases with increasing temperature from 5 to 50 K, and it is vanished above 50 K. In addition, we also worked on the magnetic entropy change around the paramagnetic to ferromagnetic phase transition. The magnetic entropy change is found as -0.87 J/kg K under 6 T magnetic field.