Growth and properties of full Heusler Co2TiSn epitaxial thin films

Abstract

Full Heusler Co2TiSn thin film were grown by DC magnetron sputtering on MgO(001) substrates at temperatures from ambient up to 800°C. The epitaxial films with full Heusler structure and high purity were achieved at 700°C with thickness ranging from ∼ 20 nm to over 1000 nm enabling deeper study of the film growth and the effect of the thickness on film properties. The state of films was investigated by wide range of techniques including atomic force and electron microscopy, X-ray diffraction and photoelectron spectroscopy, magnetometry, and magnetooptical ellipsometry supported by ab initio calculation. Structural diffraction study and magnetooptical spectral analysis reveal that under suitable deposition conditions at 700°C almost perfect L21 ordering can be attained with the [100] film direction along diagonal of cubic MgO substrate. Photoelectron spectroscopy indicated the purity of the deposited material and the fourfold symmetry of deposited films in agreement with XRD. The only downside of these films is a relatively high surface roughness as indicated by SEM and measured by AFM. Saturation magnetization at 10 K and Curie point at 370 K was comparable to bulk. The ordering as well as agreement between experimental and calculated Kerr spectra improve with increasing film thickness. In comparison the properties of Co2TiSn are similar to other alloys in the family such as Co2FeSi and Co2FeGa.