Interplay of magnetocrystalline and magnetoelastic anisotropy in epitaxial Co(10 1¯ 0) films

With the goal of creating an in-plane (IP) uniaxial anisotropy system, we deposited a thickness series of epitaxial Co(101¯0) films grown on Si(110) substrates with Ag(110) and Cr(211) buffer layers by magnetron sputtering. However, quantifying the IP magnetic anisotropy using ferromagnetic resonance measurements revealed a much more complex behavior than expected for a simple uniaxial system like hexagonally close-packed (hcp) Co. To understand the experimental results, an in-depth x-ray diffraction analysis of the film structure was performed. Even at a thickness of 100 nm, it revealed an anisotropic strain in the Co films, mainly within the Co basal plane, while the c axis remained mostly unaffected. Calculations show that such unrelaxed strain induces a significant magnetoelastic anisotropy, which counteracts the magnetocrystalline one and, as a result, reduces the overall effective anisotropy. A detailed analysis revealed that mainly the compressive strain along the Co[101¯0] out-of-plane direction is responsible for the observed magnetoelastic anisotropy, while the tensile strain along the Co[1¯21¯0] IP direction only plays a minor role.