Anomalous Tunneling in Normal Metal Junctions using Ferromagnetic Films

Abstract
Measurements of tunnel current flow through normal metal junctions made with the ferromagnetic metals Fe, Ni, and Co have been carried out in the range 1°–300°K. The insulating layer has been an oxide of the above metals or aluminum oxide and the second metal either aluminum or silver. In the case of FeFeOxAl a giant zero‐bias anomaly corresponding to a resistance maximum has been observed at helium temperatures and this persists up to room temperature. CoCoOxAl also shows a similar but smaller anomaly while NiNiOxAl shows an anomalous behavior of reverse sign. Data on the dynamic resistance as a function of voltage and temperature are presented in this paper. The effects of magnetic fields up to 50 kOe have also been studied.