Grain Size Reduction Effect on Structural and Magnetic Properties in La_1-xSr_xMnO₃ (x = 0.3 y 0.4) by Mechanical Ball Milling

We have investigated the magnetic, structural and morphological properties of ferromagnetic phases of manganite La_1-xSr_xMnO₃ with x = 0.3 (LSMO-30) and x = 0.4 (LSMO-40) prepared by solid state reaction method, and then subjected to mechanical ball milling at different times of 3, 6 and 12 h. All of the samples were characterized by X-ray diffraction (XRD) and magnetic measurements. From Rietveld analysis of XRD patterns it was found a reduction in crystallite average size (Dv) with increasing milling time, for both concentrations. For LSMO-30 sample a mix of two different crystallographic structures, an orthorhombic phase (Pnma), and another rhombohedral (R3C) were identified at 3 and 6 h, but for 12 h of milling the R3C structure was the only phase identified. In contrast, for LSMO-40 the R3C structure was discerned as the unique phase independent of milling time. For both samples, a low value of the saturation magnetization was obtained for the longer milling time (smaller Dv). This behaviour was attributed to surface effects that induce magnetically disordered states with decreasing of particle size. This magnetic anisotropy surface was also evidenced on Zeta potential values and the changes of coercive fields, which increased most drastically with the first hours of mechanical ball milling time.