Stabilization of spin-zero Ru4+ through epitaxial strain in SrRuO3 thin films

We report the stabilization of a nonmagnetic spin-zero state of Ru4+ in SrRuO3 thin films under tensile strain, resulting in suppression of the saturation magnetization relative to bulk. The magnitude of suppression as a function of strain magnitude agrees well with density functional theory predictions of the magnetic ground state of (100) oriented films. In addition to the (100) orientation, we report on the effects of tensile strain on the magnetic properties of (110) and (111) oriented SrRuO3 thin films. All films show reduced saturation magnetization as well as enhancement of the Curie temperature, a universal in-plane magnetic easy axis, and anisotropy of the saturation magnetization. Films of all orientations exhibit characteristics of a magnetic easy axis as well as higher saturation magnetizations when magnetized in the film plane rather than along the film normal. We show that all of these effects can be attributed to the tensile strain induced by growth on KTaO3 substrates and explain them in terms of an anisotropic modification of the crystal field.