Ion beam studies of single crystalline manganite thin films

Abstract

Colossal magnetoresistive manganites are oxide materials where the magnetic interactions and the electrical properties are mainly controlled by the Mn valence ratio (+3/+4). For thin films these properties present also a strong dependence on strain and microstructure. In this study we focus on doped La–Sr–MnO 3 and undoped stoichiometric LaMnO 3. The films were prepared by laser ablation using stoichiometric ceramic targets and were deposited at a substrate temperature of 770 °C on single crystalline SrTiO 3. All the films were submitted to the same in situ oxygen/heat treatment and the thicknesses were in the range of 20–500 nm. Rutherford backscattering spectrometry/channelling analysis shows the epitaxial growth of manganite films with an excellent single crystalline quality. For fully strained films, due to lattice mismatch with the substrate, we obtained minimum yields of 5% measured along the [1 0 0] growth direction. Strain relaxation leads to an increase of the minimum yield with the increase of thickness. Detailed angular scans were performed in selected films to study the misalignment along the tilt [1 1 0] and [1 1 1] directions in order to obtain an indication on the residual strain. The results were compared with X-ray diffraction and the correlation with respect to the structural quality of the films is remarkable. Moreover the magnetic measurements suggest a close relation between the transition temperature ( T c) and the strain in the films.