Spin-Glass-Like Behavior in CoO Nanoparticles and the Origin of Exchange Bias in LayeredCoO/FerromagnetStructures

The magnetic behavior of CoO nanoparticles and layered $\mathrm{CoO}/\mathrm{\text{ferromagnetic}}$ (FM) structures has been investigated by magnetization and hysteresis loop measurements. In the amorphous CoO, a large uncompensation of spins is found that is closely related to spin-glass-like behavior below a freezing temperature $T_F\approx 215–220\mathrm{K}$. The spin-glass-like phase may be described by the de Almeida–Thouless line for Ising spin systems. The exchange bias in the layered $\mathrm{CoO}/\mathrm{FM}$ structures is explained by the spin-glass-like state in the nanoparticles constituting the CoO film.