Spin-polarized electron transport in diluted magnetic semiconductors (DMS) in
the paramagnetic phase is described within the thermoballistic transport model.
In this (semiclassical) model, the ballistic and diffusive transport mechanisms
are unified in terms of a thermoballistic current in which electrons move
ballistically across intervals enclosed between arbitrarily distributed points
of local thermal equilibrium. The contribution of each interval to the current
is governed by the momentum relaxation length. Spin relaxation is assumed to
take place during the ballistic electron motion. In paramagnetic DMS exposed to
an external magnetic field, the conduction band is spin-split due to the giant
Zeeman effect. In order to deal with this situation, we extend our previous
formulation of thermoballistic spin-polarized transport so as to take into
account an arbitrary (position-dependent) spin splitting of the conduction
band. The current and density spin polarizations as well as the
magnetoresistance are each obtained as the sum of an equilibrium term
determined by the spin-relaxed chemical potential, and an off-equilibrium
contribution expressed in terms of a spin transport function that is related to
the splitting of the spin-resolved chemical potentials. The procedures for the
calculation of the spin-relaxed chemical potential and of the spin transport
function are outlined. As an illustrative example, we apply the thermoballistic
description to spin-polarized transport in DMS/NMS/DMS heterostructures formed
of a nonmagnetic semiconducting sample (NMS) sandwiched between two DMS layers.
We evaluate the current spin polarization and the magnetoresistance for this
case and, in the limit of small momentum relaxation length, find our results to
agree with those of the standard drift-diffusion approch to electron transport.Comment: Minor corrections; 3 references added; changed to single-column
forma