Temperature-dependent magnetic anomalies of CuO nanoparticles

Copper oxide (CuO) nanoparticles with an average size of 25 nm were prepared by a sol-gel method. A detailed study was made of the magnetization of CuO nanoparticles using a maximum field of 60 kOe for temperatures between 8 and 300 K. Antiferromagnetic CuO nanoparticles exhibit anomalous magnetic properties, such as enhanced coercivity and magnetic moments. Significantly, the magnitude of the hysteresis component tends to weaken upon increase in temperature (>8 K). In addition, a hysteresis loop shift and coercivity enhancement are observed at 8 K in the field-cooled (FC, at 50 kOe) case. It is thought that the change in hysteresis behavior is due to the uncompensated surface spins of the CuO nanoparticles. The susceptibility (χ) plot showed that χ varied substantially at temperatures below 12 K, and this transition is due to the exchange interactions between the neighboring atoms at the nanoscale.