Investigation of negative coercivity in one layer formation of soft and hard magnetic materials

A single layer consists of CoFe soft and LaCoFeO hard magnetic materials was deposited using the cosputtering method. Microstructure analysis of the layer demonstrated that CoFe particles were surrounded by a LaCoFeO shell and the ratio of the thicknesses was dependent on the amount of La and on the O2 (Ar+ O2) gas flow ratio used during sputtering. When the O2 (Ar+ O2) gas flow ratio was increased from 7% to 13%, coercivity (Hc) along the hard axis decreased from 11.3 Oe at 7% to -9.1 Oe at 11%. At a gas flow ratio of 13%, the coercivity increased to 11.7 Oe. The results of the present study show that negative coercivity Hc <0 is caused by interactions between two single domains of soft and hard magnetic materials. This interaction was modeled and described in detail using an extension of Heisenberg's model to the case of two domains. The results of the present study, demonstrating the conditions required to obtain negative Hc, can be applied to other pairs of soft-hard magnetic materials.