Giant magnetoresistance in helimagnets

Magnetoresistance and ordinary Hall effects are studied depending on magnetic field, temperature, electron concentration, and the orientation between the an electric field, magnetic field, and the spin spiral propagation direction. The magnetic field is assumed to be lower than the pinning value ${B}_{\mathrm{pin}}$. Solving the Boltzmann equation for a nonequilibrium distribution function, we find the giant magnetoresistance in helimagnets by more than one order of magnitude higher than in a ferromagnetic phase. The giant magnetoresistance is only observed along the spin spiral propagation axis with a magnetic field directed perpendicular to this axis. The explanation of this effect is given in terms of the spin separation of electrons along the spiral axis specific to a helical state. We study ordinary Hall effect and find that the Hall constant remains almost unchanged compared to the free electron model at the same electron concentration in low and high magnetic fields. We also observe the dramatic increase in anisotropy in the longitudinal conductivity with an applied magnetic field. The temperature dependence reveals the increase or decrease of magnetoresistance depending on electron concentration. We provide the explanations of the found effects using the simple models.