Spin-polarized electron transport in diluted magnetic semiconductors (DMS) inthe paramagnetic phase is described within the thermoballistic transport model.In this (semiclassical) model, the ballistic and diffusive transport mechanismsare unified in terms of a thermoballistic current in which electrons moveballistically across intervals enclosed between arbitrarily distributed pointsof local thermal equilibrium. The contribution of each interval to the currentis governed by the momentum relaxation length. Spin relaxation is assumed totake place during the ballistic electron motion. In paramagnetic DMS exposed toan external magnetic field, the conduction band is spin-split due to the giantZeeman effect. In order to deal with this situation, we extend our previousformulation of thermoballistic spin-polarized transport so as to take intoaccount an arbitrary (position-dependent) spin splitting of the conductionband. The current and density spin polarizations as well as themagnetoresistance are each obtained as the sum of an equilibrium termdetermined by the spin-relaxed chemical potential, and an off-equilibriumcontribution expressed in terms of a spin transport function that is related tothe splitting of the spin-resolved chemical potentials. The procedures for thecalculation of the spin-relaxed chemical potential and of the spin transportfunction are outlined. As an illustrative example, we apply the thermoballisticdescription to spin-polarized transport in DMS/NMS/DMS heterostructures formedof a nonmagnetic semiconducting sample (NMS) sandwiched between two DMS layers.We evaluate the current spin polarization and the magnetoresistance for thiscase and, in the limit of small momentum relaxation length, find our results toagree with those of the standard drift-diffusion approch to electron transport.
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