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

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 L-3,L-2 edges reveal the presence of Mn4+ in these doped ferromagnetic samples. Ferromagnetic Curie temperature (T-C) 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 Delta T-ad = 2.8 and 2.0 K for x = 0.05 and 0.1, respectively, at their respective T(C)s. On the other hand, application of 1.1 GPa hydrostatic pressure not only causes a huge shift in Tc toward higher temperature (Delta T-C approximate to 17.9 and 16.3 K for x = 0.05 and x = 0.1, respectively) but also enhances total entropy change (Delta S) for x = 0.1, while not affecting Delta S 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 possible origin of the enhanced magnetocaloric effect in x = 0.1.