Giant magnetoreistance in evaporated nanometer scale Fe/W and Co/W multilayers

Giant magnetoresistance (GMR) is often studied in multilayers (MLs) composed of mutually immiscible pairs of metals. Low miscibility is expected also in Fe/W and Co/W couples where the heat of compound formation is ΔH ≈ 0. Therefore, the GMR in these types of MLs was studied in this work. The MLs were UHV e-beam deposited onto Si, number of periods being 5 or 10. The substrate temperature was kept between 70 and 200°C. The layer thicknesses of Fe, Co and W were between 1 and 7nm, resulting in different designs. The samples were analyzed by the X-ray diffraction, X-ray reflectivity and grazing incidence X-ray diffuse scattering. The GMR was measured in the field ≤5T. In RT deposited samples, the GMR ratio was ≤0.6% even at 4.2K. It could be increased by a KrF laser irradiation. A GMR enhancement was achieved by the deposition of Fe/W MLs at 190°C. Here, the GMR ratio was 2% already at RT. At 190°C, a structural coherency and strong lateral and vertical interface roughness correlations in the MLs were found. The increase of the GMR is explained by different factors including also the elimination of magnetic shortcuts due to well-replicated and slowly varying interface profiles.