Spintronics in Nitrides
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Spintronics in Nitrides
Tomasz Dietl Laboratory for Cryogenic and Spintronic Research, Institute of Physics, Polish Academy of Sciences and ERATO Semiconductor Spintronics JST Project, al. Lotników 32/46, PL 02-668 Warszawa, Poland; also Chair of Condensed Matter Physics, Institute of Theoretical Physics, Warsaw University, ul. Hoża 69, PL 00 581 Warszawa, Poland. ABSTRACT The report of progress in studies of magnetism in the group III nitrides doped with transition metals and rare earth elements is described taking into account conclusions stemming from the recent advances in understanding of Ga1-xMnxAs, GaAs:MnAs, and related systems. The actual position of magnetic impurities in the host lattice as well as a possible role of structural, atomic, and electronic phase separation is described. The question whether the hole introduced by the Mn impurities is localized tightly on the Mn d-levels or rather on the hybridized p-d bonding states is addressed. The nature of spin-spin interactions and magnetic phases, as provided by theoretical and experimental findings, is outlined, and possible origins of high and low temperature ferromagnetism observed in these systems is discussed. Finally, the suitability of nitrides for single spin manipulation is analyzed considering linear in k spin splitting. INTRODUCTION In addition to active studies of electronic, optical, and ferroelectric properties of wide-bandgap semiconductors, over the last five years or so a rather considerable effort has been devoted to examine spin properties of these compounds with the hope to develop materials exhibiting multifunctional properties. Among relevant spintronics systems [1] one can list non-magnetic semiconductors, in which Coulomb exchange, spin-orbit couplings, and/or hyperfine interactions can be exploited to manipulate electronic and nuclear spin subsystems. Furthermore, either hybrid ferromagnetic/semiconductor structures or ferromagnetic semiconductors by combining resources of ferromagnets and semiconductors could exhibit novel functionalities [1,2]. Indeed, in addition to anisotropic, giant, and tunneling magnetoresistaces, known from earlier studies of ferromagnetic metal multilayers, a number of novel effects, including magnetization manipulations by light and electric field have been demonstrated for quantum structures of diluted ferromagnetic semiconductors, such as (In,Mn)As and p-type (Cd,Mn)Te [2]. Disappointingly, however, the application of these effects in devices is hampered by relatively low Curie temperature TC exhibiting by these systems, the highest reported TC for, e.g., (Ga,Mn)As being only about 173 K [3]. In view of potential for novel devices and system architectures two strategies were proposed to develop ferromagnetic semiconductors, in which TC would comfortably exceed the room temperature [4]. First was to increase the Mn content x and the hole concentration p in the established carrier-controlled ferromagnets, such as (Ga,Mn)As. Second was to develop new
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DMSs characterized by strong p-d hy
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