Synthesis and characterisation of fluorinated epitaxial films of BaFeO2F: tailoring magnetic anisotropy via a lowering of tetragonal distortion

In this article, we report on the synthesis and characterisation of fluorinated epitaxial films of BaFeO2F via low-temperature fluorination of thin films of BaFeO2.5+d grown by pulsed laser deposition. Diffraction measurements show that fluoride incorporation only results in a contraction of the film perpendicular to the film surface, where clamping by the substrate is prohibitive for strong in-plane changes. The fluorinated films were found to be homogenous regarding the fluorine content over the whole film thickness, and can be considered as single crystal equivalents to the bulk phase BaFeO2F. Surprisingly, fluorination resulted in the change of the tetragonal distortion to a nearly cubic symmetry, which results in a lowering of anisotropic orientation of the magnetic moments of the antiferromagnetically ordered compound, confirmed by Mössbauer spectroscopy and magnetic studies.