Space charge enhanced tunneling currents in manganites

Current–voltage characteristics I(V) with a tunneling character have been observed in selected (“electroresistive”) ceramic manganites R1−xAxMnO3 (R=La, Y; A=Ca, Ba). In this contribution, an I(V) model calculation based on spin-dependent transfer and a bipolar serial array of grains containing deGennes magnetic states are presented. The basic elements of the characteristic are so recovered, including its magnetic field (H) dependence, which in turn allows one to identify this array with a series of spin-dependent tunneling diodes connected in opposition. Besides, we find that the tunneling currents are only significant under space charge bending of the bands near the boundaries, that the electrochemical potential becomes H-field sensitive because of the spin-dependent electron state bandwidth b cos(q(H)/2) and that any slight randomness in the magnetic system will lead to hysteresis effects in the tunneling characteristic.