Low-temperature magnetotransport effects and magnetic inhomogeneity in FePt-based ferromagnetic thin films

Magnetoresistance (MR) measurements were done on a set of ferromagnetic thin films and multilayers containing different amounts of FePt alloy produced by rf sputtering. From high to intermediate temperatures (above about 10 K) the MR is explained in terms of standard mechanisms related to the granularity of samples. At lower temperatures, where R is almost independent of T , a drop in the resistance is measured, whose magnitude and position depend on the applied field. Below the drop temperature, a region of positive MR is observed around H = 0 in measurements done with the magnetic field applied either parallel or perpendicular to the film plane. The two anomalies are not explained by standard MR mechanisms; it is suggested that they can be interpreted in terms of weak localization of conduction electrons inhibited by the inner stray fields related to magnetic inhomogeneity present in all samples on the nanometre scale.