Magnetocaloric Effect and Ferromagnetic–Paramagnetic Phase Transition Study of La_0.65Ca_0.3Gd_0.05MnO₃

In this paper, the magnetocaloric properties and magnetic phase transition of the (La–Ca) MnO₃ system after secondary doping with the large magnetic moment rare earth element Gd are investigated. Analysis reveals that the polycrystalline material La_0.65Ca_0.3Gd_0.05MnO₃ exhibits a magnetocaloric effect superior to both the un-secondary doped and similar types of materials at the critical point of the ferromagnetic–paramagnetic phase transition (T_C = 173 K). Under 7 T magnetic field, the maximum magnetic entropy change |∆S_M^max|, refrigerant capacity RC, and relative cooling capacity RCP are 8.10 J kg⁻¹ K⁻¹, 350.54 J kg⁻¹, and 422.17 J kg⁻¹, respectively. The high overlap between TEC (4 K) and |∆S_M^max| at the same magnetic field indicates its good utility. Landau theory yields a negative slope of the Arrott plot at T_C, and the fit of Landau coefficients b (T_C) obtains negative values verifying the ferromagnetic–paramagnetic first-order phase transition. Further calculation of the n value and the universal curve plot using the magnetocaloric effect confirmed this type of magnetic phase transition and revealed the origin of the large magnetocaloric effect. The material provides new ideas for applications incryogenic magnetic refrigeration.