Role of Gd³⁺ on the magnetocaloric properties of lanthanum-strontium manganite

In this work, the role of magnetic ion Gd³⁺ in the crystal structure, magnetic and magnetocaloric properties of doped lanthanum-strontium manganite (La_0.7-xGd_xSr_0.3MnO₃ varying x from 0 to 0.2) synthesized by high-energy ball milling assisted with annealing, is discussed. Furthermore, the interplay between the magnetic and crystal structure in co-doped manganites is proposed. The X-ray diffraction patterns confirm the complete formation of lanthanum manganite showing different crystal structures regarding the gadolinium content. The Sr²⁺/Gd³⁺ doped lanthanum manganites with Gd³⁺ concentration lower than 0.1 mol show rhombohedral crystal structure (R-3cH). Higher gadolinium concentrations promote a phase transition from rhombohedral to orthorhombic crystal structure. The Curie temperature of the manganites decreases with an increase in Gd³⁺ content, from 376 K to 257 K, for un-doped and x = 0.2 Gd³⁺, respectively, attributed to a weakening in the double exchange interaction. Close interaction of the lattice parameters such as bond distances, bond angles, and symmetry-related with the mixed magnetic interactions was observed. The maximum magnetocaloric effect (MCE) calculated using Maxwelĺs ratio was observed around the paramagnetic to ferromagnetic ordering, at 311 K, for gadolinium content of 0.15 mol, measured through the entropy change. The Sr²⁺/Gd³⁺ doped lanthanum manganite shows a magnetically induced entropy change (|ΔSM|) in the range from 2.4 to 3.69 Jkg^-1K⁻¹ under 18 kOe, for 0.10 and 0.15, respectively, doing this manganite a suitable material for refrigeration applications at room temperature.