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

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.

Automated summary

In this study, the structural characterization, electronic structure, magnetic, and magnetocaloric properties of polycrystalline La0.7Ca0.3Mn0.9Cu0.1O3 were investigated. The sample was found to be orthorhombic single phase, and the valence state of Mn ions was confirmed to be a mixture of Mn3+ and Mn4+ based on X-ray absorption fine structure spectra. The coexistence of ferromagnetic, antiferromagnetic, and paramagnetic phases above the Curie temperature Tc was observed. The study also revealed the coexistence of first- and second-order magnetic phase transitions in the La0.7Ca0.3Mn0.9Cu0.1O3 compound.