Strain-induced magnetic anisotropies in epitaxial CrO 2 thin films probed by FMR technique

Abstract

Epitaxial CrO 2 thin films were grown onto TiO 2 (1 0 0) single-crystalline substrates by chemical vapour deposition (CVD) process with use of the solid precursor CrO 3. The CrO 2 films with thickness of 27 and 65 nm were deposited onto TiO 2 substrates pre-etched in the diluted HF. The magnetic properties of the epitaxial chromium-dioxide films have been probed by the ferromagnetic resonance (FMR) technique. Analysis of the FMR spectra shows that the magnetic behaviour of the CrO 2 films results from a competition between magnetocrystalline and strain anisotropies. The thin films are heavily strained due to lattice mismatch of CrO 2 epitaxial film with the TiO 2 single-crystalline substrate. For the thinnest film (27 nm) the stress anisotropy dominates, and the magnetic easy axis switches from the c direction to the b direction of the rutile structure. Unusual angular dependence of the resonance signal and multiple FMR modes are observed for the film with the thickness of 65 nm, where a partial strain relaxation results in appearance of two magnetic phases with mutually perpendicular easy axes along the c and b directions.