Perpendicular transport in Fe/Ge model heterostructures (original) (raw)

Based on the Kubo-Greenwood equation as formulated for layered systems, an approach is discussed that allows us to separate the resistance of the current leads from that of the region whose resistance we wish to calculate for current perpendicular to the plane of the layers. By applying this approach to Fe/Ge/Fe model structures related to the parent lattice of bcc Fe we find that at least nine layers of the magnetic electrodes should be considered as being part of the calculation in order to perform such a separation. With different structures in the Ge spacer, we find that the concentration of vacancies plays a crucial role for the existence of a sizeable magnetoresistance ͑MR͒, while the actual structure in the spacer seems to be of less importance. Depending on the type of structure and the number of spacer layers ͑in a typical regime of 6-21 layers͒ the MR for ordered structure varies between 35% and 45%. Vacancy concentrations of more than 10%, however, wipe out the MR completely. Interdiffusion at the Fe/Ge interfaces produces very similar effects.