Ferrimagnetic Clusters as the Origin of Anomalous Curie-Weiss Behavior in ZnFeO Antiferromagnetic Susceptibility.

Different studies carried out in the last three decades on the magnetic susceptibility of the spinel ZnFeO ferrite have revealed the positive character of its Curie-Weiss temperature, contradicting its observed antiferromagnetic behavior which is characterized by a well-defined susceptibility peak centered around the Neel temperature (10 K). Some approaches based on ab initio calculations and mixture of interactions have been attempted to explain this anomaly. This work shows how for very low values of the inversion parameter, the small percentage of Fe atoms located in tetrahedral sites gives rise to the appearance of ferrimagnetic clusters around them. Superparamagnetism of these clusters is the main cause of the anomalous Curie-Weiss behavior. This finding is supported experimentally from the thermal dependence of the inverse susceptibility and its evolution with the degree of inversion.