Nonlinear conductivity in weakly insulating La0.7Sr0.3Mn1-yFeyO3 (y=0.16-0.18) governed by inelastic tunneling across weak links -: art. no. 064403

Substitution of Mn by Fe in La0.7Sr0.3Mn1-yFeyO3 induces a gradual transition from a metallic ferromagnet with a high Curie temperature (T-c similar to 370 K) for y = 0, to a ferromagnetic insulator with low T-c and saturation magnetization, for y less than or similar to0.25. For an intermediate range of compositions, and at temperatures below T-c, 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.