Structural, magnetic, critical behavior and phenomenological investigation of magnetocaloric properties of La_(0.6)Ca_(0.4-x)Sr_xMnO_3 perovskite

摘要

Structural, magnetic, critical behavior and magnetocaloric properties of La0.6Ca0.4-xSrxMnO3 (x = 0.0, 0.1 and 0.4) compounds have been investigated. Rietveld refinement of the X-ray diffraction patterns indicates that our samples are pure single phase adopting the rhombohedral structure (R-3c) for x = 0.0 and the orthorombic structure (Pbnm) for x = 0.1 and 0.4. Temperature dependence of magnetization curves exhibit a second order paramagnetic (PM)/ferromagnetic (FM) phase transition at Curie temperature Tc. The critical behavior has been determined through the isothermal magnetization measurements around the critical temperature Tc by means of various techniques such as modified Arrott plot (MAP), Kouvel-Fisher (KF) method and critical isotherm analysis (CIA). The results are fully satisfactory to the requirements of the Widom scaling relation and the universal scaling hypothesis confirming their accuracy. A phenomenological model is applied to describe the magnetocaloric effect (MCE) behavior of compounds under investigation. At mu(0) H = 5T, the obtained RCP values stand for about 98, 77 and 68% of that observed in pure Gd for x = 0.0, 0.1 and 0.4, respectively, making of these materials considered as promising candidates for magnetic refrigeration applications near room temperature. By analyzing the field dependence of the magnetic entropy change data as well as the relative cooling power, it was possible to evaluate the critical exponent values which were found not only agree with those deduced from (MAP), (KF) and (CIA) methods, but they also obey the scaling theory. Our findings confirm the good correlation between the critical behavior and the MCE properties in manganite systems.