Spin conservation in circuits with a spin filter If we have a circuit made of a battery and a resistor the number of electrons with spin up will be equal to the electrons with spin down. If we put the resistor in series with a piece of ferromagnetic material which is magnetize either up or down, let's say it is magnetized up will it produce a spin polarized current? (spin down electrons wouldn't now flow in the circuit). And if current becomes spin polarized happens wouldn't  it increase electric resistance?
 A: Since you want to influence the spin of the electrons by a magnetic field, why don't we talk about the magnetic dipole of the electrons instead of their spin. At least both are connected by their alignment; under the influence of a magnetic field they get aligned with this field.
The next effect is the acting Lorentz force, in your case better called the Hall effect. The difference lies in the movement of the conductor with its electrons (Lorentz force) against the displacement of the electrons within an immovable conductor. However, in regions behind the magnetic field the forced alignment is lost immediately.
I can only think of one exception. The conductor behind the magnetic conductor is influenced by the incoming spin-polarised electrons to such an extent that its electrons align themselves with the incoming electrons and the magnetic field generated increases to such an extent that self-inductance (self-maintaining of the field) occurs. We obtain a magnetised material. Then the electrical resistance actually increases.
