Effect of titanium substitution on the structural, magnetic and magnetocaloric properties of La0.67Ba0.25Ca0.08MnO3 perovskite manganites

Abstract

We have studied the effect of Mn substitution by Ti on the structural, magnetic and magnetocaloric properties of La0.67Ba0.25Ca0.08MnTiO3 samples. All samples were synthesized using the flux method. X-ray powder diffraction showed that our samples crystallize in the rhombohedral phase R3 ¯ c space group. According to the magnetic properties, our samples present a transition from a paramagnetic to a ferromagnetic phase upon decreasing temperature. The deviation of the inverse curve of the magnetic susceptibility from Curie–Weiss law indicates the existence of a Griffiths phase. This reveals the presence of ferromagnetic clusters in paramagnetic region. Regarding the positive slopes of Arrott’s plots, the universal theory and the Landau B(T) coefficient value sign demonstrate the second-order magnetic phase transition. The magnetic entropy change was determined based to Maxwell’s relations and Landau’s theory. Near room temperature, our samples exhibited an important magnetic entropy change with maxima of 3.21 and 2.76 J kg−1 K−1, under an applied magnetic field of 5 T, respectively, for La0.67Ba0.25Ca0.08MnO3 and La0.67Ba0.25Ca0.08Mn0.95Ti0.05O3. Relative cooling power was estimated as well. It was found to reach 168 and 187 J/kg for La0.67Ba0.25Ca0.08MnO3 and La0.67Ba0.25Ca0.08Mn0.95Ti0.05O3, respectively. From the hysteresis cycles, our studied sample showed a typical soft ferromagnetic behavior with a low coercive field at 10 K. These results make our samples promising candidates for magnetic refrigeration.