Hysteresis loop of weak ferromagnetism was observed at 5 K in CuO nanosheets

A hysteresis loop of weak ferromagnetism was observed at 5 K in CuO nanosheets prepared by hydrothermal synthesis by the group of Zhao et al. [47]. Temperature dependence of magnetization showed the Neel temperature of CuO nanosheets of 219 K. The FC and ZFC data show pronounced maxima at about 40 K, which probably corresponded to blocking temperatures. Below 40 K, the magnetization increases rapidly in FC data which reconfirms the existence of weak ferromagnetism in CuO nanosheets. The influence of impurities such as Fe and Ni at low content (0.5%) was excluded as the most probable ferromagnetic material is CuFe2O4. Still, the magnetization of this phase is only half of the as-measured magnetization of CuO nanosheets. The ferromagnetism resulted from the uncompensated spins on the surface of nanomaterials, which will be orientated under a magnetic field and result in weak ferromagnetism as observed in CuO nanostructures. As the surface area of nanomaterials is much larger than that of bulk CuO, the surface effect, shown by the ferromagnetic property, becomes dominant. Hence, CuO nanomaterials will exhibit ferromagnetic properties more clearly. This argument could explain the size and morphology dependence of the ferromagnetism of CuO nanostructures, according to Bhalerao-Panajkar et al. The core-shell nature of their CuO nanoparticles with a ferromagnetic shell and antiferromagnetic core may be responsible for the bifurcation of FC-ZFC curves because, in pure antiferromagnetic or dominantly antiferromagnetic particles, no bifurcation in FC-ZFC curves occurs. The bifurcation in FC-ZFC could also arise due to the ferromagnetic shell supporting the core-shell nature of the particles. The ferromagnetic/antiferromagnetic core-shell structure was also supported by the asymmetry of the coercivity plot, which indicates the presence of an exchange field in the core/shell system, as suggested by other groups. If you are looking for high quality, high purity, and cost-effective copper oxide, or if you require the latest price, please email contact mis-asia.