Nonlinear conductivity in weakly insulating La0.7Sr0.3Mn1-yFeyO3(y = 0.16 - 0.18) governed by inelastic tunneling across weak links

Abstract

Substitution of Mn by Fe in La0.7Sr0.3Mn1-yFeyO3 induces a gradual transition from a metallic ferromagnet with a high Curie temperature (Tc∼370 K) for y = 0, to a ferromagnetic insulator with low Tc and saturation magnetization, for y ≲0.25. For an intermediate range of compositions, and at temperatures below Tc, the Ohmic resistivity and thermopower are consistent with electronic transport through percolating paths, embedded in an insulating medium and disrupted by weak links. Pulsed I - V measurements show that in the nonlinear regime, the excess current density obeys a power-law dependence on the electric field over 2-5 orders of magnitude (of current density). The results indicate that the major contribution to the excess current is due to inelastic tunneling via pairs of states localized in the weak links. © 2001 The American Physical Society.