Abstract
The intrinsic objective of this work is to investigate the structural (RX, MEB, TGA and IR) and magnetic properties of La1 La1-x⎕xMnO3 (x = 0.1; 0.2 and 0.3) series prepared through the sol–gel method. All these systems crystallize in the rhombohedral structure, $$ {{\rm R}\bar{3}{\rm c}} $$ space group, with the presence of a secondary phase for x = 0.3. We recorded the increase of a unit cell volume when the La deficiency amount increases, which refers to the fact that the vacancy is characterized by a radius other than zero. Another point that can be quoted is the increase of Mn–O–Mn bond angle and the decrease of Mn–O length with lanthanum deficiency (x), confirming the increase of the unit cell volume. The evaporation of water rose by the weight loss as a function of temperature in all samples. The FT-IR measurement revealed one peak corresponding to the Mn–O bond; this can be explained by the Jahn–Teller effect where the Mn ion makes an internal movement against the MnO6 octahedron. The thermal variation of the magnetization indicates the existence of a paramagnetic–ferromagnetic transition at Curie temperature with the increase of lanthanum deficiency. Saturation magnetization and Curie temperature increased with x (0.1; 0.2 and 0.3) deficiency. Hysteresis cycles confirm the ferromagnetic character at low temperatures and paramagnetic state with temperature increase. The increase of saturation magnetization can be accounted for in terms of the change of high spin Mn3+ to low spin Mn4+. Departing from the study of magnetic properties in terms of Arrott plots, the nature of magnetic transitions proves to be of second order.
Published Version
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