Tuning the magnetocaloric properties of lanthanum–strontium manganite by rare-earth Nd³⁺ doping

This study investigated the effect of neodymium (Nd) on the crystal structure and magnetocaloric properties of lanthanum–strontium manganites (La_0.7−xNd_xSr_0.3MnO_3, 0 ≤ x ≤ 0.4), synthesized by assisted high-energy ball milling. Rietveld analysis from X-ray diffraction disclosed that Nd³⁺ did not promote crystallographic phase transitions. The rhombohedral crystal structure remained in the R-3c space group for all the compositions, with slight changes in lattice parameters. The defect model allowed the quantification of the Mn⁴⁺ occupancy, which is in the range from 0.20 to 0.26 mol, for 0.1 and 0.4 mol of Nd³⁺, respectively. The presence of Mn⁴⁺ promoted further ferromagnetic interactions, increasing systematically the saturation magnetization, from 65 A·m²·kg⁻¹ to 73 A·m²·kg⁻¹, and a diminution in the Curie temperature from 364 to 255 K, for 0 and 0.4 mol of Nd³⁺, respectively, obtained by temperature-dependent magnetization measurements. The doped manganite with 0.35 mol of Nd³⁺ showed a maximum of entropy change of 3.73 Jkg⁻¹ K⁻¹ at 1.8 T near room temperature, with a relative cooling power of 82 Jkg⁻¹ and temperature-averaged entropy change, TEC(3) and TEC(10), of 3.53 and 3.06 Jkg⁻¹ K⁻¹, respectively. It is demonstrated that the presence of Nd³⁺ modulates the Curie temperature near room temperature and enhances the magnetocaloric properties at low magnetic fields, making these manganites a promising material for magnetocaloric applications.