Research on spintronics has galvanized the design of new devices that
exploit the electronic spin in order to augment the performance of current
microelectronic technologies. The sucessful implementation of these devices
is largely contingent on a quantitative understanding of nonequilibrium magnetism
in conducting ferromagnets. This thesis is largely devoted to expanding
the microscopic theory of magnetization relaxation and current-induced spin
torques in transition metals ferromagnets as well as in (III,Mn)V dilute magnetic
semiconductors.
We start with two theoretical studies of the Gilbert damping in electric
equilibrium, which treat disorder exactly and include atomic-scale spatial
inhomogeneities of the exchange field. These studies enable us to critically review
the accuracy of the conventional expressions used to evaluate the Gilbert
damping in transition metals. We follow by generalizing the calculation of the Gilbert damping to
current-carrying steady states. We find that the magnetization relaxation
changes in presence of an electric current. We connect this change with the
non-adiabatic spin transfer torque parameter, which is an elusive yet potentially
important quantity of nonequilibrium magnetism. This connection culminates
in a concise analytical expression that will lead to the first ab initio
estimates of the non-adiabatic spin transfer torque in real materials.
Subsequently we predict that in gyrotropic ferromagnets the magnetic
anisotropy can be altered by a dc current. In these systems spin-orbit coupling,
broken inversion symmetry and chirality conspire to yield current-induced spin
torques even for uniform magnetic textures. We thus demonstrate that a
transport current can switch the magnetization of strained (Ga,Mn)As.
This thesis concludes with the transfer of some fundamental ideas from
nonequilibrium magnetism into the realm of superconductors, which may be
viewed as easy-plane ferromagnets in the particle-hole space. We emphasize
on the analogies between nonequilibrium magnetism and superconductivity,
which have thus far been studied as completely separate disciplines. Our
approach foreshadows potentially new effects in superconductors. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/6579 |
| Date | 20 October 2009 |
| Creators | Garate, Ion |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Format | electronic |
| Rights | Copyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works. |
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