Effect of thickness on structure, microstructure, residual stress and soft magnetic properties of DC sputtered Fe < inf > 65 < /inf > Co < inf > 35 < /inf > soft magnetic thin films

Abstract

The effect of film thickness on structure, microstructure, residual stress and soft magnetic properties of Fe65Co35 thin films deposited on Si(001) and MgO(001) substrates was investigated by varying film thickness from 30 to 600 nm. X-ray diffraction studies showed that the FeCo films are polycrystalline in the as-deposited condition irrespective of deposition on Si or MgO substrate. The microstructure of films consisted of spherical grains for 30 nm film thickness and columnar grains for all other film thicknesses. The grain size for the films was found to increase from 15 to 50 nm with increasing film thickness. The sputtered films also exhibited tensile residual stresses with the magnitude of stress decreasing with increasing film thickness. The Fe65Co35 films deposited on both substrates also exhibited very good in-plane soft magnetic properties with a saturation magnetization 4πMs of ~23.6-23.8 kG and coercivity of ~27-30 Oe without any under-layer only for films with thickness of 30 nm. For all other thicknesses, these films exhibited a significantly higher coercivity. The observed variations in soft magnetic properties with film thickness were explained in terms of residual stress and microstructure of the films. © 2014 Elsevier B.V.