The spin-dependent electron transport has been studied in magnetic semiconductor waveguides (nanowires) in the helical magnetic field. We have shown that -- apart from the known conductance dip located at the magnetic field equal to the helical-field
amplitude $B_h$ -- the additional conductance dips (with zero conductance) appear at magnetic field different from $B_h$. This effect occuring in the non-adiabatic regime is explained as resulting from the resonant Landau-Zener transitions between the spin-splitted subbands.
A proposal of a spin separator based on the spin Zeeman effect in Y-shaped nanostructure with a quantum point contact is presented. Our calculations show that the appropriate tuning of the quantum point contact potential and the external magnetic fie
ld leads to the spin separation of the current: electrons with opposite spins flow through the different output branches. We demonstrate that this effect is robust against the scattering on impurities. The proposed device can also operate as a spin detector, in which -- depending on the electron spin -- the current flows through one of the output branches.
