We investigate spin-polarized transport through semimagnetic semiconductor heterostructures under the influence of both an external electric field and a magnetic field. The structural symmetric and asymmetric effects as well as the electric-field effect are stressed. The results indicate that (1) transmission resonances are drastically suppressed for spin electrons tunneling through the symmetric heterostructure under an applied bias; and (2) transmission resonances can be enhanced to optimal resonances for spin-up electrons tunneling through the asymmetric structure with double paramagnetic layers under a certain positive bias, while for spin-down ones tunneling through the same structure, resonances can also be enhanced to optimal resonances under a certain negative bias. Transmission suppression and enhancement originate from magnetic- and electric-field-induced and structure-tuned potentials. Spin-dependent resonant enhancement and negative differential resistances can be clearly seen in the current density. The results shown in this work might shed light on design and applications of spintronic devices.

• Received 6 February 2001

DOI:https://doi.org/10.1103/PhysRevB.63.214415