Structural, magnetic and transport study of monovalent Na-doped manganite Pr0.55Na0.05Sr0.4MnO3

The manganite Pr0.55Na0.05Sr0.4MnO3 prepared by solid state reaction has the orthorhombic structure and mean crystallite size of 51 nm. Scanning electron microscopy (SEM) shows that the grains are irregularly spherical like shaped with sizes 400 to 700 nm. In vicinity of Curie temperature equal to 289 K the magnetic entropy change |ΔSMmax| attains 1.75 J kg−1 K−1 under an applied magnetic field of 2 T which corresponds to relative cooling power of 93 J/kg. Electrical resistivity measurements reveal a transition from metallic to semiconductor phase. Temperature variation of electrical resistivity was fitted by the small polaron hopping (SPH) and Mott’s Variable range Hopping (VRH) models. The activation energy and Mott temperature are found to decrease and N(EF) to increase in magnetic field varying from zero to 1 T. The phonon contribution dominates in thermal conductivity.

► Characterization of new monovalent doped manganite Pr0.55Na0.05Sr0.4MnO3 with crystallite size of 51 nm.
► Maximum magnetic entropy change achieves 1.75 J/kg K and large RCP about 93 J/kg for the applied magnetic field of 2 T.
► Magnetoresistance reaches −13% at 25 K and gradually decaying with increasing temperature is related to grain boundaries.
► Combined analyses of thermal and electrical conductivities show that phonons play the overwhelming role in heat transport.
► Manganite is suitable for magnetic refrigeration technology at room temperature.