Electronic Structure, Griffiths Phase, and Magnetocaloric Effect in La0.7Ca0.3Mn1-xCuxO3 (x=0.1) showing first- and second-order characters

Abstract

We investigate the structural characterization, electronic structure, magnetic, and magnetocaloric properties of polycrystal-line La0.7Ca0.3Mn0.9Cu0.1O3 fabricated by a solid-state reaction method. XRD analysis indicates the orthorhombic single phase of the sample. The X-ray absorption fine structure spectra of Mn K-edge prove that the valence state of Mn ions is in mixed states of Mn3+ and Mn4+. The inverse of magnetic susceptibility chi(-1) as a function of temperature indicates coexistence of ferromagnetic, anti-ferromagnetic, and paramagnetic phase above Curie temperature T-C. Based on M(H) isotherms, the temperature dependences of magnetic entropy change (Delta S-m) under different magnetic field changes (Delta H=0-50 kOe) have been estimated. For Delta H= 50 kOe, the maximum value of Delta S-m (vertical bar Delta S-max vertical bar) is found to be about 2.0 J kg(-1) K-1, corresponding to the relative cooling power (RCP) of 240 J/kg. Interestingly, the H/M versus M-2 curves at temperature around T-C exhibit a positive slope under applied fields below 20 kOe, whereas they exhibit a negative slope at higher applied fields 20 kOe. Additionally, all Delta S-m (T) data under Delta H=0-15 kOe collapse into a universal curve of normalized entropy change (Delta S-m/Delta S-max) versus resealed temperature (theta), with theta=(T - T-C)/(T-r - T-C) and T-r is the reference temperature. In contrast, Delta S-m (T) data under Delta H= 20-50 kOe do not obey the universal curve of Delta S-m/Delta S-max. versus theta. These behaviors suggest a coexistence of the first- and second-order magnetic phase transition in La0.7Ca0.3Mn0.9Cu0.1O3 compound.