Low-temperature resistivity minimum in ceramic manganites

Abstract

Measurements of magnetoresistance and magnetization were carried out on ceramic samples of La0.5Pb0.5MnO3 and La0.5Pb0.5MnO3, containing 10 at. % Ag in a dispersed form. The results obtained for the resistivity at zero applied magnetic field exhibit a shallow minimum at the temperature T∼25–30 K which shifts towards lower temperatures upon applying a magnetic field and disappears at a certain field Hcr. Also the resistivity at helium temperature decreases upon applying magnetic fields. It is shown that the model of charge carriers tunneling between antiferromagnetically coupled grains may account for the results observed.

Disorder effects at low temperatures in La0.7−xYxCa0.3MnO3 manganites

“…A similar low-temperature minimum of the resistivity was also observed in manganite thin films [23], and its origin has been discussed in detail by Rozenberg et al [24]. They argue against an interpretation in terms of weaklocalization effects, in which case the field dependence would be much weaker, and interpret the resistivity behavior as due to spin-polarized inter-grain tunneling conduction.…”

“…With such a model, the following expression for the low-temperature resistivity is proposed in Ref. [24]:…”

Intrinsic and precipitate-induced quantum corrections to conductivity in La2/3Sr1/3MnOGao1, Cao2, Zhang3 et al. 2012Phys. Rev. B

“…[12][13][14][15] Extensive experimental and theoretical work has been performed, and several mechanisms have been discussed to interpret these resistivity minima. Amongst them are mechanisms based on spin-polarized tunnelling via grain boundaries, 16 Kondo-like effects ( magnetic-and charge-type), [17][18][19] and quantum interference effects (QIE) arising from electron-electron interactions and weak localization, 1,12 just to name a few. However, a clear picture has not yet emerged and is still under discussion 9,20 impeding our understanding of the physics of correlated electron systems.…”

Large negative magnetoresistance in reactive sputtered polycrystalline GdNx films

“…The resistivity reaches a minimum at 15 K and then increases as temperature further decreases, which can be attributed to the charge carriers tunneling between grains. 27 MRÀH curves of GdN x films are shown in Figs. 2(a)-2(d), where the magnetic field is perpendicular to the film plane.…”

“…27 The question is why only the film fabricated at f N2 ¼ 20 sccm shows the significantly enhanced MR at low fields, which should be caused by the different spin polarization in the films with different N vacancies. For clarifying this point, Figures 4(a)-4(d) show the electronic band structure of a GdN 2 Â 2 Â 2 supercell without and with N vacancies.…”