Multifaceted Roles of Ag<sup>+</sup> Ions within and outside La–Ca–MnO<sub>3</sub> Perovskite Manganites: Unveiling the Room Temperature Magnetocaloric Effect
Pramod R. Nadig, Olivier Toulemonde, A. Perumal, M.S. Murari, Mamatha D. Daivajna
Abstract
High Resolution Image Download MS PowerPoint Slide 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 (–Δ S M ) for the lower substitution ( x = 0.05) is found to be 4.5 J/kg K, achieved at 273.5 K for Δ H = 20 kOe, while the same is retained at about 4.25 J/kg K for higher substitution ( x = 0.2). Remarkably, −Δ S 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 (Δ T H–C = 3 K) and TEC (Δ T 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.