An Enhancement in the Magnetocaloric Effect in a Composite Powder Based on Lanthanum Manganites

This study presents a dual-phase lanthanum manganite ceramic composite based on a mixture of equal weight ratios of La0.7Ca0.2Sr0.1MnO3 and La0.7Ca0.25Sr0.05MnO3 designed to enhance the magnetocaloric effect (MCE) of individual compounds, under a low magnetic field (≤18 kOe). X-ray diffraction (XRD) analysis revealed the coexistence of two orthorhombic manganite phases corresponding to the individual compounds, with no secondary phases detected. Temperature-dependent magnetization measurements in the composite evidenced two Curie temperatures at 286.8 K and 307.6 K, reflecting the effect of Ca2+ and Sr2+ concentrations. Arrott plots and β parameters confirmed that the phase transition is of second order. Although the maximum magnetic entropy change (ΔSM) of the composite is slightly lower than that of the individual manganite phases, its relative cooling power (RCP) reaches 188.82 J·kg−1, with an extended operational temperature window (OTW) of approximately 85 K, spanning from around 243 K to 328 K. This broad OTW enables efficient operation over a wider temperature range compared to similar materials, such as the individual La0.7Ca0.2Sr0.1MnO3 and La0.7Ca0.25Sr0.05MnO3 compounds, which exhibit an RCP of 55.24 and 65.12 J·kg−1, respectively, under a comparable magnetic field (~18 kOe). The improved magnetocaloric performance is attributed to interfacial exchange coupling and strain-mediated effects that broaden the ΔSM response and generate a non-additive RCP. These results demonstrate that interphase coupling and microstructural tuning effectively broaden the operating temperature range for magnetic refrigeration under moderate fields, making this composite a strong candidate for practical cooling applications.