Impact of Gd Substitution on the Structure, Magnetic Ordering, and Magnetocaloric Response of La0.67Ca0.33MnO3

Abstract

A comprehensive investigation of the structural, magnetic, and magnetocaloric properties of polycrystalline La_0.67−xGd_xCa_0.33MnO₃ (x = 0, 0.05, 0.1, 0.15, and 0.2), synthesized by the solid-state method, has been carried out. X-ray diffraction confirmed that all compositions crystallize in a single-phase orthorhombic Pbnm structure. A systematic decrease in the Curie temperature, from 257 K (x = 0) to 61 K (x = 0.2), was observed and attributed to the suppression of double-exchange interactions and the emergence of magnetic inhomogeneity. Most notably, the substitution of Gd led to a pronounced enhancement in the magnetic entropy change (|ΔS_M|), reaching a maximum of 11.24 J/kg K under a 5 T field for the x = 0.2 composition, which stands as one of the highest values reported for manganites. In addition, a secondary anomaly in the entropy change curves, particularly at elevated fields, was associated with a field-induced metamagnetic transition arising from the coexistence of paramagnetic and antiferromagnetic states above T_C. Critical behavior analysis based on Arrott plots further revealed that all samples exhibit a first-order magnetic phase transition. These simultaneous observations of exceptionally large ΔS_M values and metamagnetic features highlight the potential of these rare-earth-modified manganites for high-performance magnetocaloric applications.