Magnetoresistance of ferromagnetic point junctions from tunneling to direct contact regimes

The behavior of magnetoresistance in NiFe (permalloy) point junctions was investigated using an STM set-up, where the junction resistance was continuously varied from 10⁸ Ω-10³ Ω. Our results reveal an enhancement of magnetoresistance of more than 80% at one conductance quantum, and the decaying magnetoresistance as one moves away from 12.9 kΩ to either the diffusive regime or the tunneling regime, as supported by independent theories on spin-dependent transport. The suppression of magnetoresistance with incorporation of a 35-nm-thick Au barrier was observed, as well as the dependence of magnetoresistance on the relative orientations of the electrodes.