Studies on the structure, critical behavior and magnetocaloric effect in (LaBi)SrCoO cobaltite

摘要

In the present paper, we report the structure, the magnetic, the critical behavior, the magnetocaloric properties and the universal curve of La_(0.45)Bi_(0.15)Sr_(0.4)CoO_3 cobaltite. Polycrystalline sample was synthesized in air by the solid state reaction method at a sintering temperature of 1200 ℃. Phase purity, structure, size, and crystallinity were investigated using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The Reitveld refinement of XRD pattern shows that the sample adopts a rhom-bohedral system with R3c space group. Critical exponents obtained by the modified Arrott plot technique, Kouvel-Fisher method, and critical isothermal analysis are close to the theoretical prediction of 3D Heisenberg model values, revealing the characteristic of short-range ferromagnetic interactions. With these values, the M(T,µ_0H) relations below and above the curie temperature collapse into two universal branches in the asymptotic critical region following the scaling equation. Moreover, the experimental magnetic entropy changes measured for various fields collapse onto a master curve, confirming the universal behavior of the magnetocaloric effect in this system. Particularly, its magnetic-field dependence obeys a power-law fitting, where the exponent n = 0.98 is quite far from the value calculated at Curie temperature from the critical exponents. This difference is related to the magnetic inhomogeneity in the sample.