Structure, phase transitions, 55Mn NMR and magnetoresistive properties of Pr0.6-x NdxSr0.3Mn1.1O3-δ (x=0-0.6)

Ceramic samples of Pr0.6-xNdxSr0.3Mn1.1O3-delta (x = 0-0.6) were studied by x-ray diffraction, resistive, magnetic (chi(ac) and Mn-55 NMR), magnetoresistive and electron microscopy methods. It was shown that with increasing the concentration x, the type of unit cell distortion changes from orthorhombic (x = 0-0.2) to pseudo-cubic (x = 0.4-0.6), and the imperfection of the structure, which contains anion and cation vacancies, is increased. A decrease in the temperatures of metal semiconductor (T-ms) and ferromagnetic paramagnetic (T-C) phase transitions and an increase in the resistivity and activation energy with increasing x was explained by an increase in the concentration of vacancies, which weakens high-frequency electronic double-exchange Mn3+ <-> Mn4+. It was found that the compositions with a higher content of neodymium exhibit a transition to the antiferromagnetic state at temperatures below 130K, Two types of magnetoresistive effects were observed. The magnitude of the first effect, which occurs near the phase transition temperatures T-ms and T-C, increases with concentration x. The magnitude of the second effect, which was observed at low temperatures, exceeds that of the first one. The magnetic phase diagrams which describe strong correlations between the composition, structure defects, phase transitions, and functional characteristics, including magnetoresistive effect, were constructed. (C) 2014 AIP Publishing LLC.