Dopant-dependent spin–lattice coupling in La0.7Ca0.15Sr0.15MnO3: Fe/Co/Ni effects on magnetocaloric properties

In this paper, La_0.7Sr_0.15Ca_0.15Mn_0.95A_0.05O₃ (A = Fe, Co and Ni) were fabricated via the sol–gel (S-G) approach. The samples are all rhombohedral structure shapes and belong to the trigonal space group R-3c, as shown by XRD. ZEISS Gemini SEM 300 scans showed irregular sub-micron particles with decreasing particle size for La_0.7Sr_0.15Ca_0.15Mn_0.95A_0.05O₃ (A = Fe, Co and Ni). The magnetic properties were characterized utilizing an MPMS, and the magnetocaloric effects (MCE) were further investigated. The investigations of La_0.7Sr_0.15Ca_0.15Mn_0.95A_0.05O₃ (A = Fe, Co and Ni) found that their Curie temperatures (Tc) were 289.5 K, 290.2 K, and 300 K, respectively. The maximum magnetic entropy change (\(-\Delta {S}_{M}^{max}\)) for La_0.7Sr_0.15Ca_0.15Mn_0.95A_0.05O₃ (A = Fe, Co and Ni) at 5 T is 5.107 J/(kg∙K), 4.177 J/(kg∙K) and 3.852 J/(kg∙K), and the relative cooling power (RCP) is 264.819 J/kg, 275.3409 J/kg and 288.7435 J/kg. The Arrott curve, normalization and Curie–Weiss law (CW) fit together to determine that the second-order ferromagnetic-to-paramagnetic (FM-to-PM) transition is observed in the three samples, along with a small magnetic hysteresis and thermal hysteresis, the super-exchange interactions (SE) and the double-exchange interactions (DE) competed with each other to increase half peak width and RCP, with La_0.7Sr_0.15Ca_0.15Mn_0.95A_0.05O₃ (A = Ni) having the largest RCP. While conventional low-temperature magnetic materials need to work in a liquid helium environment, room-temperature magnetic materials do not need to rely on extreme cooling conditions, which greatly reduces the cost of refrigeration equipment, and thus room-temperature magnetically cooled materials have a greater potential for research and development. In this paper, Ni is used as the doping element, and its RCP can reach 288.7435 J/kg, and its Tc is close to room temperature, so it is possible to be used as a room-temperature magnetic cooling material.