The effect of Jahn–Teller distortion on the magnetic and magnetocaloric effect in La-doped gadolinium barium manganite

Disorder in the mixed valence perovskites Gd_0.7-xLa_xBa_0.3MnO₃ (where x = 0, 0.1, 0.2, and 0.4) was observed due to the chemical inhomogeneity resulting to the Jahn–Teller (JT) distortions, which is primarily attributed to the differences in cationic size and the ratio between JT active and non-JT active ions. Magnetocaloric effect of Gd_0.7Ba_0.3MnO₃ remains unexplored. The completely different electronic structure of La³⁺, if it is substituted for Gd³⁺ can lead to interesting results. The powder x-ray diffraction (P-XRD) and Rietveld refinement analysis showed the effect of La³⁺ doping in Gd³⁺ sites on distortion caused by electron density imbalance. The JT parameter (σ_JT) shows the change in the JT distortion due to La doping is initially diminished by increases as a function of increase in La doping. Surface morphology of samples was analyzed and particles size around 1–2 µm was measured with no agglomeration. Elemental mappaing and elemental composition from the energy dispersive x-ray spectroscopy (EDX) confirm the stoichiometry and homogenity of the synthesized samples. X-ray photoelectron spectroscopy (XPS) authenticates the mixed oxidatation states, which is futher corrobated with the bond valance calculation. As a result, double exchange interaction in the system is enhanced and have a greater influence on the magnetocaloric effect in addition to Griffiths phase of the perovskite structure in all the samples which can be identified from the temperature vs inverse susceptibility graphs. From the results we can see that the Neel temperature increases as a function of σ_JT. The change in the magnetic entropy of Gd_0.7-xLa_xBa_0.3MnO₃ (x = 0, 0.1, 0.2, and 0.4) was observed as negative (− ΔS_M = 0.7, 0.35, 0.65, and 0.8 J/kg K) and magnetic phase transition moved towards room temperature that is favourable for magnetic refrigeration.