2 research outputs found
Anisotropic tunneling magnetoresistance and tunneling anisotropic magnetoresistance: spin-orbit coupling in magnetic tunnel junctions
The effects of the spin-orbit interaction on the tunneling magnetoresistance
of ferromagnet/semiconductor/normal metal tunnel junctions are investigated.
Analytical expressions for the tunneling anisotropic magnetoresistance (TAMR)
are derived within an approximation in which the dependence of the
magnetoresistance on the magnetization orientation in the ferromagnet
originates from the interference between Bychkov-Rashba and Dresselhaus
spin-orbit couplings that appear at junction interfaces and in the tunneling
region. We also investigate the transport properties of
ferromagnet/semiconductor/ferromagnet tunnel junctions and show that in such
structures the spin-orbit interaction leads not only to the TAMR effect but
also to the anisotropy of the conventional tunneling magnetoresistance (TMR).
The resulting anisotropic tunneling magnetoresistance (ATMR) depends on the
absolute magnetization directions in the ferromagnets. Within the proposed
model, depending on the magnetization directions in the ferromagnets, the
interplay of Bychkov-Rashba and Dresselhaus spin-orbit couplings produces
differences between the rates of transmitted and reflected spins at the
ferromagnet/seminconductor interfaces, which results in an anisotropic local
density of states at the Fermi surface and in the TAMR and ATMR effects. Model
calculations for Fe/GaAs/Fe tunnel junctions are presented. Furthermore, based
on rather general symmetry considerations, we deduce the form of the
magnetoresistance dependence on the absolute orientations of the magnetizations
in the ferromagnets.Comment: 17 pages, 10 figure
Semiconductor Spintronics
Spintronics refers commonly to phenomena in which the spin of electrons in a
solid state environment plays the determining role. In a more narrow sense
spintronics is an emerging research field of electronics: spintronics devices
are based on a spin control of electronics, or on an electrical and optical
control of spin or magnetism. This review presents selected themes of
semiconductor spintronics, introducing important concepts in spin transport,
spin injection, Silsbee-Johnson spin-charge coupling, and spindependent
tunneling, as well as spin relaxation and spin dynamics. The most fundamental
spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling.
Depending on the crystal symmetries of the material, as well as on the
structural properties of semiconductor based heterostructures, the spin-orbit
coupling takes on different functional forms, giving a nice playground of
effective spin-orbit Hamiltonians. The effective Hamiltonians for the most
relevant classes of materials and heterostructures are derived here from
realistic electronic band structure descriptions. Most semiconductor device
systems are still theoretical concepts, waiting for experimental
demonstrations. A review of selected proposed, and a few demonstrated devices
is presented, with detailed description of two important classes: magnetic
resonant tunnel structures and bipolar magnetic diodes and transistors. In most
cases the presentation is of tutorial style, introducing the essential
theoretical formalism at an accessible level, with case-study-like
illustrations of actual experimental results, as well as with brief reviews of
relevant recent achievements in the field.Comment: tutorial review; 342 pages, 132 figure