INFLUENCE OF BALL MILLING PROCESS ON STRUCTURAL AND MAGNETIC PROPERTIES OF La0.7Sr0.3MnO3 MANGANITE
INFLUENCE OF BALL MILLING PROCESS ON STRUCTURAL AND MAGNETIC PROPERTIES OF La0.7Sr0.3MnO3 MANGANITE
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This investigation presents the magnetic and structural properties of ferromagnetic manganite La0.7Sr0.3MnO3, (LSMO), subjected to ball milling processes. The LSMO powder sample was obtained by solid state reaction from high purity precursors. From x-ray diffraction (xRD), the sample showed the characteristic peaks of this phase. By means of thermogravimetric analysis (TGA) assisted by magnetic field, used as first method to measure the Curie temperature TC, the NM (non-milling) LSMO powders exhibited a TC=369.69 K (96.96 oC), which agrees with the magnetization measurements. In order to study size dependent properties, LSMO powder was subjected to mechanical milling pro- cesses during 3, 6 and 12 hours. From Rietveld refinement of xRD patterns, a reduction in crystallite average size (Dv) and a stabilization of crystalline structure (the R3c space group), with milling time (tM), were observed. These results are consistent with the Scanning Electron Microscopy (SEM) images, which showed more homogeneity in the grain distri- bution with longer milling times. From magnetic characterization results, it was found that the saturation magnetization decreases with decreasing grain size (smaller Dv). This behavior is attributed to surface effects that induce magnetically disordered states in smaller particle sizes. However, the TC is kept constant around 365 K and it is independent of tM.
Abstract: Este trabajo estudia las propiedades estructurales y magnéticas de la manganita La0,7Sr0,3MnO3 (LSMO) ob- tenida por el método de reacción en estado sólido y sometida a procesos de molienda mecánica. En las medidas de difracción de rayos x, xRD, la muestra en polvo de LSMO presentó los picos característicos de esta fase. La técnica de termogravimetría (TGA) asistida con campo magnético, mostró una temperatura de Curie TC = 369,69 K (=96,96 oC). Este resultado concuerda con la temperatura de la transición magnética, cercana a 365 K. Con el fin de analizar la dependencia de las propiedades magnéticas y estructurales en relación con el tamaño de partícula, las muestras se sometieron a molienda mecánica por 3, 6 y 12 horas. A partir de refinamiento Rietveld de los rayos x, se observó una reducción de tamaño de partícula y una estabilización de la estructura cristalina de grupo espacial R3c, a medida que aumenta el tiempo de molienda tM. Esto es consistente con las imágenes de SEM, que mostraron más homogeneidad de la distribución de tamaño a mayor tM. En las medidas de magnetización en función de la temperatura, se encontró que la magnetización de saturación decrece con la disminución de tamaño de grano (Dv pequeños). Este comportamiento es atribuido a estados magnéticamente desordenados que se generan en la superficie. Sin embargo, la temperatura crítica se mantiene constante alrededor de 365 K e independiente de tM.
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