Low-temperature resistivity anomalies and magnetic field-induced transitions in neodymium-based manganites

Abstract

To investigate the magnetotransport behaviour of Nd0.67A0.33MnO3 (where A=Ca, Sr, Pb and Ba) materials, samples were prepared by the sol–gel route. The materials were characterized by x-ray diffraction (XRD) and it was found that all the samples have orthorhombic structure with pnma space group. All the samples except Nd0.67Ca0.33MnO3 (NCMO) were found to exhibit a clear metal-to-insulator (M–I) transition. Nd0.67Ca0.33MnO3, however, was found to exhibit an M–I transition on applying a magnetic field of 5 T and this transition was strengthened when the field was enhanced to 8 T. The field-induced transition in NCMO may be attributed to the presence of ferromagnetic clusters in an antiferromagnetic matrix. Further, all the samples were found to show an upturn in resistivity at about 30 K, and the observed behaviour can be explained based on theory that it is a combined effect of weak localization, the Kondo effect and electron–electron and electron–phonon scattering. Finally, the magnetoresistance (MR) of NCMO is found to be as high as 99%, indicating that it may be exploited for some devices.

Metal–Insulator Transition Induced by Spin Reorientation in Fe7Se8 Grain Boundaries

“…The magnetic field dependence of the resistivity provides more evidence for the validity of the above model. Our results are different from the previously reported resistivity minima, where a significant change in the resistivity can be obtained with different applied fields (up to 42% with a field of 8 T in neodymium-based manganites, 25 and 200% at 5 T in manganese perovskites 26 ). In our case, the resistivity only decreases by 0.5% in a field of 4 T. Aleiner et al 27 considered a quantum correction to the electrical conductivity due to the influence of an external magnetic field.…”