Physica E 13 (2002) 525–528 www.elsevier.com/locate/physe Non-linear spin transport in magnetic semiconductor multiple quantum wells David S anchez a; b; c ; * , A.H. MacDonald b; c , Gloria Platero a a Instituto de Ciencia de Materiales de Madrid (CSIC), Cantoblanco, 28049 Madrid, Spain b Department of Physics, Indiana University, Bloomington, IN 47405, USA c Department of Physics, The University of Texas at Austin, Austin, TX 78712, USA Abstract We present a theoretical model for vertical transport in DC-biased magnetically-doped II–VI semiconductor multiple quantum wells. Non-, partly- and fully-polarized spin distributions are taking into account within a self-consistent scheme. We investigate the formation of electric eld domains under the combined inuence of band electron interactions with polarized local moments and spin relaxation processes. ? 2002 Elsevier Science B.V. All rights reserved. PACS: 72.25.Dc; 72.25.Mk; 73.21.Cd; 75.50.Pp Keywords: Magnetic semiconductors; Spin transport; Multiple quantum wells Novel physical properties and promising tech- nological devices have emerged from the interplay between quantum connement and spin-polarized transport [1]. Of special interest are magnetic semi- conductor (MS) heterostructures as engineered sys- tems for the manipulation of both the electron charge and the spin [2]. In particular, Mn doped II–VI semiconductor compounds can be manipulated to give rise to strongly spin-polarized electronic sys- tems [3]. The heteroepitaxy of modulation-doped wide-gap II–VI MS quantum wells (QWs) [4] and ZnSe= (Zn,Cd,Mn)Se superlattices [5] results in the fabrication of two-dimensional electron gas (2DEG) systems ferromagnetically coupled to Mn +2 magnetic ions. In DC-biased non-magnetic multiple quantum wells (MQWs) the competition between charge ac- cumulation and resonant tunneling eects results in * Corresponding author. Tel.: +34-913349000; fax: +34- 913720623. E-mail address: dsanchez@icmm.csic.es (David S anchez). the formation of electric eld domains (EFDs) [6]. As a result, the current voltage (I –V ) characteristics presents sawtooth-like branches in the negative dier- ential conductance (NDC) region. Along each branch two nearly uniform electric elds regions develop, separated by a domain wall (DW) of accumulated electrons. Including the spin degree of freedom in the study of vertical (i.e., in the growth direction) trans- port is expected to supply new features to the physics of EFD formation. Here we deal with the formation of EFDs in weakly coupled II–VI MQWs with one magnetic QW. We nd rich behavior due to the strong non-linearity of the system and because of the space dependence of the band electron spin polarizations. In II–VI MQWs the conduction electrons and the Mn local moments are coupled by means of an ex- change interaction which favors the alignment of the Mn and the band electron spins. Within the mean-eld and virtual crystal approximation [7] the eect of this interaction is to make the jth subband energy of the 1386-9477/02/$ - see front matter ? 2002 Elsevier Science B.V. All rights reserved. PII:S1386-9477(02)00186-8