Nonequilibrium order parameter dynamics in spin and pseudospin ferromagnets

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Title: Nonequilibrium order parameter dynamics in spin and pseudospin ferromagnets
Author: Garate, Ion
Abstract: 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 .
URI: http : / /hdl .handle .net /2152 /6579
Date: 2009-10-20


Nonequilibrium order parameter dynamics in spin and pseudospin ferromagnets. Doctoral dissertation, The University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /6579 .

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