Magnetic and Magnetocaloric Effects and Phase Transition Critical Behavior of Dy-Doped La0.7Ca0.3MnO3

In this study, polycrystalline samples of La_0.7Ca_0.3-xDy_xMnO₃ (x = 0, 0.15) were synthesized via the solid-state reaction method. Their structures, magnetic properties, magnetocaloric effects, and critical behaviors associated with phase transitions were systematically investigated. All samples exhibited structures belonging to the Pbnm space group, characterized by precise compositions and good single-phase. The samples underwent paramagnetic-ferromagnetic (PM-FM) phase transitions at Curie temperatures (T_C) of approximately 244 K for x = 0 and 132 K for x = 0.15. The incorporation of Dy significantly broadened the half height wide temperature range (ΔT_FWHM) from 39.36 K (x = 0) to 121.92 K (x = 0.15). Consequently, the relative cooling capacity (RCP) of the samples was markedly increased, rising from 369.76 J·kg⁻¹ (x = 0) to 721.09 J·kg⁻¹ (x = 0.15). Furthermore, upon doping with x = 0.15, the phase transition type shifted from the first-order phase transition (FOPT) of the parent phase to a second-order phase transition (SOPT). This shift is attributed to the substitution of some Ca²⁺ ions by Dy³⁺, which weakened the double-exchange interaction and altered the phase transition type. Analysis of the critical behavior using the Kouvel-Fisher (K-F) and Modified Arrott plot (MAP) methods revealed that the critical features of the phase transition in La_0.7Ca_0.15Dy_0.15MnO₃ are better described by a Mean-Field Model with long-range ordering. Therefore, this study not only enriches our understanding of the physical properties of this class of materials but also enhances their potential for magnetic refrigeration (MR) applications.