Effect of particle size reduction on the structural, magnetic properties and the spin excitations in ferromagnetic insulator La0.9Sr0.1MnO3 nanoparticles

The La0.9Sr0.1MnO3 (LSMO) compound was prepared by the citrate-gel method and annealed at different temperatures (H6, H8, H10 and H12). X-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetic measurements were used to investigate the particle size effects on the physical properties. All samples were found to be single phase and crystallize in rhombohedral symmetry with R3¯c space group except for the H12 sample, whose refinement has revealed the coexistence of both R3¯c rhombohedral and Pbnm orthorhombic phases. It was also found that the reduction of grain size intensively affects the magnetic properties of these compounds. The variation in the magnetic properties as a function of the particle size may be explained in terms of a core–shell model. The reduction of the Curie temperature with increasing grain size is explained as the strain effect of grain induced by the distortion at grain boundaries and the orthorhombic strain caused by the strong JT coupling. The temperature dependence of magnetization based on a thermal distribution of spin waves and fit results to a power law Tα shows a deviation from Bloch low and α deviates from 1.50 to 2.88 as the particle size decreases from 94.9 to 44.98 nm. The experimental magnetization measurements at 5 K were interpreted in the framework of a random magnetic anisotropy model. From the analysis of the approach to saturation magnetization some fundamental parameters have been extracted, quantifying the anisotropy forces.