Specularity in GMR spin valves and in situ electrical and magnetotransportmeasurements

An experimental four-point probe For in situ electrical and magnetotranspor t transport measurements during film growth is described. This method is un ique in that it can capture thickness-dependent evolution of not only condu ctance but also magnetoresistance in a UHV deposition chamber. It has been used to monitor the growth of single layer, spin valve and multilayer struc tures and to measure specularity and interface scattering, both spin-indepe ndent and spin-dependent. Addition of similar to1 monolayer of Co to Cu sur face causes the net film conductance to decrease sharply, but the reverse c ase of Cu on Co shows a strong positive curvature of the thickness-dependen t 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 valv e or metal thin film to oxygen for an appropriate time may lead to an appre ciable enhancement of specularity of its top surface. This leads to an incr ease in the sheet conductance, much more so when the free layer and pinned layer magnetizations are parallel than antiparallel, In contrast, previousl y reported specularity enhancement due to noble metal overlayers has not be en observed by the in situ experiments.