Multifaceted Roles of Ag⁺ Ions within and outside La-Ca-MnO₃ Perovskite Manganites: Unveiling the Room Temperature Magnetocaloric Effect

The primary objective of this study is to unravel the role of Ag⁺ ions in A-site substitutions and to explore their potential in achieving room-temperature magnetocaloric response. The investigation is structured around three distinct scenarios: direct Ag⁺ substitution, Ag⁺ introduction as a composite, and the absence of Ag⁺ as an A-site deficient system. Through these approaches, the study seeks to elucidate the multifaceted roles played by Ag⁺ ions, providing valuable insights into their influence on structural and magnetic properties. In the case of Ag⁺ substitution at the A-site, temperature-dependent magnetization reveals a two-step dependence with distinctive inflection points, attributed to the Curie points of the Pnma and R3̅c phases, respectively. As a consequence, the maximum value of the isothermal magnetic entropy change (-ΔS_M) for the lower substitution (x = 0.05) is found to be 4.5 J/kg K, achieved at 273.5 K for ΔH = 20 kOe, while the same is retained at about 4.25 J/kg K for higher substitution (x = 0.2). Remarkably, −ΔS_M peaks at room temperature of 306.5 K in case of x = 0.2. Furthermore, an effective screening is undertaken, evaluating the figure-of-merit to elucidate the suitability and efficacy of the material. The temperature-averaged entropy change (TEC) values, TEC (ΔT_H-C = 3 K) and TEC (ΔT_H-C = 5 K), reached 4.15 and 4.09 J/kg K, respectively, under a low magnetic field change of 20 kOe. Overall, the tuning of the phase transition without compromising the low-field magnetocaloric response was achieved solely through substitution, highlighting its pivotal role over composite and deficient systems.