  Magnetoelectronics is mainly digital, i.e. governed by up and down
magnetizations. In contrast, analogue magnetoelectronics makes use of phenomena
occuring for non-collinear magnetization configurations. Here we review
theories which have recently been applied to the transport in non-collinear
magnetic nanostructures in two and multiterminal structures, viz. random matrix
and circuit theory. Both are not valid for highly transparent systems in a
resistive environment like perpendicular metallic spin valves. The solution to
this problem is a renormalization of the conventional and spin-mixing
conductance parameters.
