High Magnetization and High Electrical Resistivity in Dense Fe and Fe-Co Cluster Assemblies Prepared by Energetic Cluster Deposition

Abstract

Using a plasma-gas-condensation-type cluster deposition apparatus, positively charged Fe and Fe-Co alloy clusters have been deposited on a negatively biased substrate together with their neutral clusters. In these cluster assemblies the packing density and saturation magnetization per volume, M_s, monotonically increase, while the magnetic coercivity, H_c, rapidly decreases with increasing the bias voltage, V_a. For the dense Fe and Fe₇₀Co₃₀ cluster assemblies prepared at V_a=−20 kV, M_s=1.78 and 2.01 T, respectively and H_c<80 A/m, whereas the electrical resistivity, ρ≈1 and 3 μΩ m, respectively. These results indicate that the cluster assembling is a fascinating method to obtain excellent soft magnetic materials with high electrical resistivity because the magnetic exchange coupling between ferromagnetic clusters is so strong as to overcome the magnetic anisotropy of individual clusters and the conduction electrons are scattered by the cluster interfaces.