Electrical and Magnetic Properties of Co/CoO Core-Shell Clusters

The need of increasing the density in magnetic recording media motivates the studies on magnetic clusters. In this context, we present a study of the magnetic transport properties in granular systems consisting in layers of cobalt-cobalt oxide core-shell clusters. The cluster diameter is 4 to 5 nm, with an approximately 1 nm oxide shell. The low temperature magnetoresistance and magnetization indicate the effect of exchange bias. The magnetoresistance behavior depends on the distribution of the clusters magnetic moments direction and on the electronic mean free path. The association of magnetoresistance and magnetization measurements reveals the local correlations between magnetic moments. The correlation length is calculated from the resistance versus reduced magnetization curve: in the absence of cluster-cluster correlation, one expects a parabolic shape. The deviation from this behavior corresponds to the correlations between the magnetic moments of the clusters at the length scale of the mean free path.