Specularity in GMR spin valves and in situ electrical and magnetotransport measurements

An experimental four-point probe for in situ electrical and magnetotransport measurements during film growth is described. This method is unique in that it can capture thickness-dependent evolution of not only conductance but also magnetoresistance in a UHV deposition chamber. It has been used to monitor the growth of single layer, spin valve and multilayer structures and to measure specularity and interface scattering, both spin-independent and spin-dependent. Addition of ~1 monolayer of Co to Cu surface causes the net film conductance to decrease sharply, but the reverse case of Cu on Co shows a strong positive curvature of the thickness-dependent conductance. Most of the observed interface scattering may be intrinsic, arising from a high density of empty d-states at Cu boundaries that result in increased electron scattering. It is confirmed that exposing a spin valve or metal thin film to oxygen for an appropriate time may lead to an appreciable enhancement of specularity of its top surface. This leads to an increase in the sheet conductance, much more so when the free layer and pinned layer magnetizations are parallel than antiparallel. In contrast, previously reported specularity enhancement due to noble metal overlayers has not been observed by the in situ experiments