Tunnel-type GMR in metal-nonmetal granular alloy thin films

Previously, a tunnel type of giant magnetoresistance (GMR) was discovered in a sputtered Co-base CoAlO granular alloy thin film, which was characteristic in exhibiting GMR of about 8% accompanying a large specific electrical resistivity of the order of 104 μΩ cm, due to a weak tunnel conductance in the metal-nonmetal granular structure of this alloy. In this paper, it has been found that GMR changes depending on O content and appears with a maximum near the percolation threshold point from metallic conductance to tunnel conductance in CoAlO granular alloy thin films. In addition, superparamagnetic behavior in the magnetic field and temperature dependencies of magnetization have been found for the GMR alloy films. The observations support the spin-dependent tunneling effect for this new GMR.