Strain Induced Nanopillars and Variation of Magnetic Properties in La_0.825Sr_0.175MnO_3/LaAlO_3 Films

To investigate the process of strain relaxation and resultant variation of microstructure and magnetic properties, low-doped La_0.825Sr_0.175MnO_3 epitaxial films with different thicknesses are deposited on LaAlO_3 substrates and strain induced nanopillars are discovered inside the La_0.825Sr_0.175MnO_3 film. Perpendicular oriented nanopillars mainly exist below 30 nm and tend to disappear above 30 nm. The distribution of nanopillars not only induce the variation of lattice parameters and local structural distortion but also lead to the deviation of easy magnetization axis from the perpendicular direction. Specifically, the out-of-plane lattice parameters of the film decrease quickly with the increase of the thickness but tend to be constant when the thickness is above 30 nm. Meanwhile, the variations of magnetic properties along in-plane and out-of-plane directions would also decline at first and they then remain nearly unchanged. Our work constructs the relationship between nanopillars and magnetic properties inside films. We are able to clearly reveal the effects of inhomogeneous strain relaxation.