Temperature dependence of exchange anisotropy in monodisperse cobalt nanoparticles with a cobalt oxide shell

Exchange anisotropy was studied by SQUID magnetometry on an array of monodisperse colloidal nanoparticles consisting of a 7–8 nm diameter FCC Co core covered with a 2–2.5 nm thick FCC CoO shell. Temperature-dependent measurements of the exchange bias field show that the exchange anisotropy vanishes when a magnetic field was applied during cooling below 150 K. The suppression of exchange anisotropy is due to uncompensated interfacial antiferromagnetic spins. [Copyright &y& Elsevier]