  The electrical resistance of ferromagnetic/normal-metal (F/N)
heterostructures depends on the nature of the junctions which may be tunnel
barriers, point contacts, or intermetallic interfaces. For all junction types,
the resistance of disordered F/N/F perpendicular spin valves as a function of
the angle between magnetization vectors is shown to obey a simple universal
law. The spin-current induced magnetization torque can be measured by the
angular magnetoresistance of these spin valves. The results are generalized to
arbitrary magnetoelectronic circuits.
