Large Magnetocaloric Effect in Cu-Doped La_0.7Ca_0.3MnO₃ Compounds

Abstract

The structural characterization, and the electronic, magnetic and magnetocaloric properties of polycrystalline samples of La_0.7Ca_0.3Mn_1−xCu_xO₃ (x = 0, 0.04, 0.06, 0.08) have been investigated. X-ray powder diffraction analysis indicates all samples having an orthorhombic structure, belonging to the Pbnm space group. X-ray absorption fine structure spectra reveal that Mn is in the mixed state of Mn³⁺ and Mn⁴⁺ while Cu has divalent state (Cu²⁺). With the substitution of Cu²⁺ for Mn, the Curie temperature, T_C, decreases monotonically from 248 K for x = 0 to 156 K for x = 0.08, which is due to weakened exchange interactions. The downturn in the temperature dependencies of the inverse magnetic susceptibility, χ⁻¹(T), curves observed above T_C for x = 0 and 0.08 is characteristic of the Griffiths-like phase. The analysis of isothermal magnetization data M(T, H) based on the Banerjee’s criteria has indicated x = 0, 0.04, and 0.06 samples undergoing a first-order magnetic phase transition. However, the x = 0.08 sample, the coexistences of second-order magnetic phase transition at low magnetic fields below 8 kOe and first-order magnetic phase transition at high magnetic fields were observed. The maximum magnetic entropy change measured at a magnetic field span of 50 kOe occurring near the T_C decreases from 10.3 to 4.8 J/kg.K with increasing x from 0 to 0.08. However, the relative cooling power (RCP) tends to increase, in which a maximum RCP of 360 J/kg for x = 0.08 that is about 1.3 times greater than that observed for the parent sample (x = 0).