Soft anisotropic high magnetization Cu/FeCo films

Abstract

A remarkable reduction in the coercivity Hc of sputtered Fe65Co35 films from 9.6 to 0.7 kA/m was observed using a Cu underlayer as thin as 2.5 nm. The FeCo without Cu exhibited a wide distribution of anisotropy fields up to >80 kA/m while the FeCo with Cu showed a well-defined in-plane uniaxial anisotropy field of 2.3 kA/m up to FeCo thicknesses of at least 1 μm. The saturation magnetostriction was (4.7±0.4)×10−5, independent of Cu thickness while the in-plane tensile stress gradually decreased from 2 to 0.2 GPa as the Cu thickness increased to 10 nm. The Cu changed the preferred orientation of the FeCo from (100) to (110) but more significantly reduced the average grain size from ∼50 to ∼9 nm. This alone is sufficient to explain quantitatively the reduction in Hc using Hoffmann’s ripple theory.