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 polycrystalline 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 휒−1 as a function of temperature indicates coexistence of ferromagnetic, anti-ferromagnetic, and paramagnetic phase above Curie temperature TC. Based on M(H) isotherms, the temperature dependences of magnetic entropy change (ΔSm) under different magnetic field changes (ΔH=0–50 kOe) have been estimated. For ΔH=50 kOe, the maximum value of ΔSm (|ΔSmax|) 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 M2 curves at temperature around TC exhibit a positive slope under applied fields below 20 kOe, whereas they exhibit a negative slope at higher applied fields 20 kOe. Additionally, all ΔSm(T) data under ΔH =0–15 kOe collapse into a universal curve of normalized entropy change (ΔSm/ΔSmax) versus rescaled temperature (θ), with θ=(T−TC)/(Tr−TC) and Tr is the reference temperature. In contrast, ΔSm(T) data under ΔH=20–50 kOe do not obey the universal curve of ΔSm/ΔSmax versus θ. These behaviors suggest a coexistence of the first- and second-order magnetic phase transition in La0.7Ca0.3Mn0.9Cu0.1O3 compound.