We have investigated theoretically the spin-polarised tunnelling current th
rough a triple-barrier structure based on semimagnetic semiconductors. In t
his device the resonant tunnelling for each spin state is achieved at diffe
rent bias, yielding well defined peaks in the I-V curve that have high degr
ee of spin polarisation. Spin-flip scattering gives rise to additional peak
s in the I-V curve when the alignments of the levels with opposite spins oc
cur. We have used perturbation theory to treat the spin-dependent scatterin
g mechanism, which in our model is driven by the thermal fluctuation of the
ion magnetic moments. A double-barrier-tunnelling device has also been inv
estigated, in which we found current with high degree of spin polarisation,
even when the aforementioned spin-flip mechanism is considered. This devic
e has potential applications as a spin filter. (C) 2000 Elsevier Science B.
V. All rights reserved.