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Enhanced Magnetocaloric Effect Driven by Hydrostatic Pressure in Na-Doped LaMnO₃

Das, Rajasree, Midya, Arindam, Kumari, Mukesh, Chaudhuri, Anindita, Yu, Xiaojiang, Rusydi, Andrivo, Mahendiran, Ramanathan
Journal of physical chemistry 2019 v.123 no.6 pp. 3750-3757
X-ray absorption spectroscopy, ambient pressure, entropy, hydrostatic pressure, magnetic fields, manganese, physical chemistry, specific heat, spectral analysis, temperature, thermal expansion
We compare the impact of hydrostatic pressure on the magnetic and magnetocaloric properties in monovalent alkali earth ion-doped polycrystalline La₁–ₓNaₓMnO₃ (x = 0.05, 0.10). X-ray absorption spectra of Mn L₃,₂ edges reveal the presence of Mn⁴⁺ in these doped ferromagnetic samples. Ferromagnetic Curie temperature (TC) obtained from the temperature dependence of magnetization is 249.7 K for the x = 0.05 and 269.6 K for x = 0.1 samples in ambient pressure. A magnetic field change of 3T causes an adiabatic temperature change of ΔTₐd = 2.8 and 2.0 K for x = 0.05 and 0.1, respectively, at their respective TCs. On the other hand, application of 1.1 GPa hydrostatic pressure not only causes a huge shift in TC toward higher temperature (ΔTC ≈ 17.9 and 16.3 K for x = 0.05 and x = 0.1, respectively) but also enhances total entropy change (ΔS) for x = 0.1, while not affecting ΔS for x = 0.05. Specific heat and linear thermal expansion coefficient measurements suggest a possibility of structural transition below the paramagnetic–ferromagnetic transition in x = 0.1, which is absent in x = 0.05. Pressure-driven enhancement of structural transition temperature could be a possible origin of the enhanced magnetocaloric effect in x = 0.1.