Thickness dependence on the surface morphology and the magnetic microstructure of a0.7Sr0.3MnO3 films under different strains

We have characterized ferromagnetic La0.7Sr0.3MnO3 thin films, of various thickness (in the range 500–1500 Å) grown by pulsed laser deposition on different substrates such as (0 0 1)-SrTiO3, (0 0 1)-LaAlO3, (1 1 0)-NdGaO3 and (0 0 1)-LaSrGaO4, using atomic force microscopy (AFM) and magnetic force microscopy (MFM). AFM reveals an island-like growth surface morphology on all substrates. Both the roughness and the average grain size increase with the thickness of the film. Two types of magnetic patterns are imaged at room temperature (in the ferromagnetic state) with MFM. The first one, obtained for films grown on (0 0 1)-LaAlO3 and (0 0 1)-LaSrGaO4 substrates, shows “circular” droplets (or bubbles) contrasted domains revealing the existence of films with an easy direction of magnetization, M, out of the plane of the film. In this type of pattern, the average size of the bubbles increases with the thickness of the film. The second magnetic pattern, obtained in the case of (0 0 1)-SrTiO3 and (0 0 1)-NdGaO3 substrates, shows uniform color domains without contrasted domains implying the existence of films with an easy direction of magnetization, M, in the plane of the film. For such films, the MFM magnetic patterns are similar for each thickness. This study highlights the importance of the substrate choice and the thickness of the film on the magnetic microstructure of La0.7Sr0.3MnO3 films.