Effect of pinholes in magnetic tunnel junctions

The electron transport in magnetic tunnel junction containing pinholes is studied, where ferromagnetic layers make direct contact through narrow conducting channels. The transport is treated within the Landauer formalism using a tight-binding Hamiltonian. It is found that a narrow pinhole induces a resonant tunneling behavior causing a magnetoresistance that oscillates with the bias voltage. After averaging over pinholes of various shapes, the oscillation and magnitude of magnetoresistance (MR) are reduced, which can explain how barrier roughness diminishes the MR. For a pinhole of a large radius, where the number of atoms inside is much larger than 1, an enhanced MR is obtained whose value is similar to an all-metal giant magnetoresistance spin valve.