Exchange bias in macroporous Co/CoO

The magnetic properties of new magnetic material, macroporous cobalt have b een investigated. The cobalt samples studied have FCC close packed three-di mensional arrays of spherical pores (pore size roughly 300 nm). These sampl es were prepared by colloidal crystal templating. The hysteresis loops of t he field-cooled samples of macroporous cobalt were, shifted along the field axis with the shift consistent with the exchange bias phenomenon. The exch ange bias is attributed to antiferromagnetic CoO, which most likely forms w hen the samples are exposed to the ambient atmosphere. The temperature depe ndence. of the exchange bias and coercivity of these samples was investigat ed. The temperature dependence of the coercivity was found to be non-monoto nic. We proposed a possible explanation of this behavior in terms of a spin -glass-like state of cobalt nanoparticles that forms below 45 K (C) 2001 El sevier Science B.V. All rights reserved.