Modulation of Microstructure, Magnetic, and Magnetocaloric Properties in La0.80Ag0.20MnO3 via Eu/Pb Co-Doping

Four perovskite manganite samples, La0.80Ag0.20MnO3 (LA), La0.78Eu0.02Ag0.20MnO3 (LEA), La0.80Pb0.05Ag0.15MnO3 (LPA), and La0.77Eu0.03Pb0.05Ag0.15MnO3 (LEPA), were prepared by the Pechini sol–gel method. The samples were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and a magnetic property measurement system. A systematic investigation was conducted into the individual effects of Eu and Pb doping, as well as their co-doping, on the microstructural, magnetic and magnetocaloric properties of the materials. The results show that all samples are mainly composed of a rhombohedral perovskite phase with the R3¯c space group, accompanied by a trace amount of Ag. Addition of Eu3+ and Pb2+ induces lattice contraction and expansion, respectively. Under the same processing conditions, the average crystallite and particle sizes of the LEA sample (45.3 nm and 0.18 μm) are smaller than those of the other three samples (69.6~80.6 nm and 0.38~0.44 μm), indicating that the introduction of Eu alone suppresses crystallization ability, which can be avoided through Eu/Pb co-doping. All samples undergo a second-order ferromagnetic–paramagnetic transition, and the Curie temperature TC shifts to either lower or higher temperatures upon the introduction of Eu or Pb alone (from 310.8 K to 298.0 K or 318.0 K, respectively), which is attributed to the variation of the Mn3+/Mn4+ double-exchange (DE) interaction resulting from the ionic size mismatch and lattice distortion. In the LPA sample, an additional contribution arises from the altered Mn3+/Mn4+ ratio and enhanced DE interaction caused by the substitution of Pb2+ for Ag+. By modifying the Eu/Pb ratio, the TC of the LEPA sample was tuned to 299.3 K, and its maximum magnetic entropy change was enhanced to 3.90 J·kg−1·K−1 (∆H = 2 T). These results indicate that multicomponent synergistic regulation can improve the magnetocaloric performance of La-based perovskite manganites, providing a useful strategy for the development of room-temperature magnetic refrigeration materials.