Bias Voltage Dependence of GMR in Insulating Granular Thin Films

Abstract

The bias voltage (V_b) dependence of tunnel-type GMR was investigated in Co-Al-O insulating granular thin films. The electrical resistivity (ρ) and MR were measured in the current-perpendicular-to-plane (CPP) geometry for 1-μm-thick Co-Al-O films sandwiched between Au-Cr or Nb-Ti electrodes. The MR was found to remain constant until V_b reached a threshold voltage, whereas ρ decreased rapidly with V_b. The MR started to decrease when V_b exceeded the threshold voltage. This behavior is discussed in terms of the inelastic tunneling process with magnon excitations, which causes the decrease in MR.