Bulk contributions to tunnel magnetoresistance in magnetic tunnel junctions -: art. no. 094423

We have carefully designed an experiment to elucidate the interface and bulk contributions to spin-polarized transport in CoFe-based magnetic tunnel junctions (MTJ's). We demonstrated that the bulklike contribution to tunneling magnetoresistance (TMR) exists in the magnetic tunneling process, which is determined by the tunneling characteristic length of the ferromagnetic electrodes. This characteristic length in MTJ's is different from the spin diffusion length in metallic based spin valves or magnetic multilayers due to the fundamental different transport behaviors in two structures. The experiment designed with a wedge-shaped CoFe layer inserted at the interface between the insulating barrier and reference electrode offers a unique and simple way to determine this characteristic length, which is about 0.8 nm for the CoFe electrode. For interfacial contributions to dominate TMR, the magnetic electrodes should have a very short tunneling characteristic length of atomic scale.