Spin filtering effect at inserted interfaces in perpendicular spin valves

Giant magnetoresistance can be enhanced by insertion of a nonmagnetic spacer in the ferromagnetic free layer of perpendicular spin valves. The enhancement and its independence of the inserted spacer thickness are argued in terms of the two-current series-resistor model, and interpreted in a simple picture that the interfaces between the inserted spacer and the parallel ferromagnetic layers act as spin filters. Magnetization of the laminated free layers behaves similarly to that of the single one; it indicates its applicability to the magnetic read head.