Electric-Field—Dependent Magnetoresistance in Ferromagnetic Semiconductors

Changes in the sign of the longitudinal magnetoresistance as a function of applied magnetic and electric fields are observed in single crystals of $p$-type Cd${\mathrm{Cr}}_{2}$${\mathrm{Se}}_{4}$. A phenomenological theory for the non-Ohmic behavior associated with spin-wave-carrier interaction is developed, and its comparison with the experimental results indicates the existence of spin-wave amplification by the drifting carriers. All the experimental results can be explained in terms of spin-wave-carrier interaction and spin-disorder scattering.