Alvaro S. Núñez
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Previous Organizations / Institutes
The organizations / institutes from the scholar's other articles in the past ten years
Research Subjects
Alvaro S. Núñez has a total of 8 co-authors. Here are the top co-authors by number of shared publications:
- R. A. Duine
Institute for Theoretical Physics, Utrecht University, Leuvenlaan 4, 3584 CE Utrecht, The Netherlands
10 shared publications - Allan H. MacDonald
Department of Physics, University of Texas at Austin, Austin, USA
8 shared publications - P. M. Haney
Department of Physics, The University of Texas at Austin, 1 University Station C1600, Austin, Texas 78712-0264, USA
6 shared publications - D. Waldron
Centre for the Physics of Materials and Department of Physics, McGill University, Montreal, Quebec, Canada H3A 2T8
3 shared publications - Hong Guo
College of Physics and Energy, Shenzhen University, Shenzhen 518060, China
3 shared publications - Jairo Sinova
Institut für Physik, Johannes Gutenberg Universität Mainz, Mainz, Germany
2 shared publications
Latest Publications
- Open Access
Effective temperature and Gilbert damping of a current-driven localized spin
Starting from a model that consists of a semiclassical spin coupled to two leads we present a microscopic derivation of the Langevin equation for the direction of the spin. For slowly-changing direction it takes on the form of the stochastic Landau-Lifschitz-Gilbert equation. We give expressions for the Gilbert damping parameter and the strength of the fluctuations, including their bias-voltage dependence. At nonzero bias-voltage the fluctuations and damping are not related by the fluctuation-dissipation theorem. We find, however, that in the low-frequency limit it is possible to introduce a voltage-dependent effective temperature that characterizes the fluctuations in the direction of the spin, and its transport-steady-state probability distribution function.
Open AccessEffective temperature and Gilbert damping of a current-driven localized spin
Starting from a model that consists of a semiclassical spin coupled to two leads we present a microscopic derivation of the Langevin equation for the direction of the spin. For slowly-changing direction it takes on the form of the stochastic Landau-Lifschitz-Gilbert equation. We give expressions for the Gilbert damping parameter and the strength of the fluctuations, including their bias-voltage dependence. At nonzero bias-voltage the fluctuations and damping are not related by the fluctuation-dissipation theorem. We find, however, that in the low-frequency limit it is possible to introduce a voltage-dependent effective temperature that characterizes the fluctuations in the direction of the spin, and its transport-steady-state probability distribution function.
- 1 February 2008
- Published by American Physical Society (APS) in Physical Review B
- Vol. 77 (5) , 054401
Effective temperature and Gilbert damping of a current-driven localized spin
Starting from a model that consists of a semiclassical spin coupled to two leads, we present a microscopic derivation of the Langevin equation for the direction of the spin. For slowly changing direction, it takes on the form of the stochastic Landau-Lifschitz-Gilbert equation. We give expressions for the Gilbert damping parameter and the strength of the fluctuations, including their bias-voltage dependence. At nonzero bias voltage, the fluctuations and damping are not related by the fluctuation-dissipation theorem. We find, however, that in the low-frequency limit, it is possible to introduce a voltage-dependent effective temperature that characterizes the fluctuations in the direction of the spin, and its transport-steady-state probability distribution function.
- 1 February 2008
- Published by American Physical Society (APS) in Physical Review B
- Vol. 77 (5) , 054401
Effective temperature and Gilbert damping of a current-driven localized spin
Starting from a model that consists of a semiclassical spin coupled to two leads, we present a microscopic derivation of the Langevin equation for the direction of the spin. For slowly changing direction, it takes on the form of the stochastic Landau-Lifschitz-Gilbert equation. We give expressions for the Gilbert damping parameter and the strength of the fluctuations, including their bias-voltage dependence. At nonzero bias voltage, the fluctuations and damping are not related by the fluctuation-dissipation theorem. We find, however, that in the low-frequency limit, it is possible to introduce a voltage-dependent effective temperature that characterizes the fluctuations in the direction of the spin, and its transport-steady-state probability distribution function.
- Open Access
Functional Keldysh Theory of Spin Torques
We present a microscopic treatment of current-induced torques and thermal fluctuations in itinerant ferromagnets based on a functional formulation of the Keldysh formalism. We find that the nonequilibrium magnetization dynamics is governed by a stochastic Landau-Lifschitz-Gilbert equation with spin transfer torques. We calculate the Gilbert damping parameter $\alpha$ and the non-adiabatic spin transfer torque parameter $\beta$ for a model ferromagnet. We find that $\beta \neq \alpha$, in agreement with the results obtained using imaginary-time methods of Kohno, Tatara and Shibata [J. Phys. Soc. Japan 75, 113706 (2006)]. We comment on the relationship between $s-d$ and isotropic-Stoner toy models of ferromagnetism and more realistic density-functional-theory models, and on the implications of these relationships for predictions of the $\beta/\alpha$ ratio which plays a central role in domain wall motion. Only for a single-parabolic-band isotropic-Stoner model with an exchange splitting that is small compared to the Fermi energy does $\beta/\alpha$ approach one. In addition, our microscopic formalism incorporates naturally the fluctuations needed in a nonzero-temperature description of the magnetization. We find that to first order in the applied electric field, the usual form of thermal fluctuations via a phenomenological stochastic magnetic field holds.Open AccessFunctional Keldysh Theory of Spin Torques
We present a microscopic treatment of current-induced torques and thermal fluctuations in itinerant ferromagnets based on a functional formulation of the Keldysh formalism. We find that the nonequilibrium magnetization dynamics is governed by a stochastic Landau-Lifschitz-Gilbert equation with spin transfer torques. We calculate the Gilbert damping parameter $\alpha$ and the non-adiabatic spin transfer torque parameter $\beta$ for a model ferromagnet. We find that $\beta \neq \alpha$, in agreement with the results obtained using imaginary-time methods of Kohno, Tatara and Shibata [J. Phys. Soc. Japan 75, 113706 (2006)]. We comment on the relationship between $s-d$ and isotropic-Stoner toy models of ferromagnetism and more realistic density-functional-theory models, and on the implications of these relationships for predictions of the $\beta/\alpha$ ratio which plays a central role in domain wall motion. Only for a single-parabolic-band isotropic-Stoner model with an exchange splitting that is small compared to the Fermi energy does $\beta/\alpha$ approach one. In addition, our microscopic formalism incorporates naturally the fluctuations needed in a nonzero-temperature description of the magnetization. We find that to first order in the applied electric field, the usual form of thermal fluctuations via a phenomenological stochastic magnetic field holds. - 5 July 2007
- Published by American Physical Society (APS) in Physical Review B
- Vol. 76 (2) , 024404
Current-induced order parameter dynamics: Microscopic theory applied tospin valvesTransport currents can alter order parameter dynamics and change steady states in superconductors, in ferromagnets, and in hybrid systems. In this paper, we present a scheme for fully microscopic evaluation of order parameter dynamics that is intended for application to nanoscale systems. The approach relies on time-dependent mean-field theory, on an adiabatic approximation, and on the use of nonequilibrium Green’s function theory to calculate the influence of a bias voltage across a system on its steady-state density matrix. We apply this scheme to examine the spin-transfer torques which drive magnetization dynamics in spin-valve structures. Our microscopic torques are peaked near interfaces, in agreement with most previous pictures, but surprisingly act mainly on Co transition metal orbitals rather than on orbitals as generally supposed.- 5 July 2007
- Published by American Physical Society (APS) in Physical Review B
- Vol. 76 (2) , 024404
Current-induced order parameter dynamics: Microscopic theory applied tospin valvesTransport currents can alter order parameter dynamics and change steady states in superconductors, in ferromagnets, and in hybrid systems. In this paper, we present a scheme for fully microscopic evaluation of order parameter dynamics that is intended for application to nanoscale systems. The approach relies on time-dependent mean-field theory, on an adiabatic approximation, and on the use of nonequilibrium Green’s function theory to calculate the influence of a bias voltage across a system on its steady-state density matrix. We apply this scheme to examine the spin-transfer torques which drive magnetization dynamics in spin-valve structures. Our microscopic torques are peaked near interfaces, in agreement with most previous pictures, but surprisingly act mainly on Co transition metal orbitals rather than on orbitals as generally supposed.- 18 June 2007
- Published by American Physical Society (APS) in Physical Review B
- Vol. 75 (21) , 214420
Functional Keldysh theory of spin torques
We present a microscopic treatment of current-induced torques and thermal fluctuations in itinerant ferromagnets based on a functional formulation of the Keldysh formalism. We find that the nonequilibrium magnetization dynamics is governed by a stochastic Landau-Lifschitz-Gilbert equation with spin-transfer torques. We calculate the Gilbert damping parameter and the nonadiabatic spin transfer torque parameter for a model ferromagnet. We find that , in agreement with the results obtained using imaginary-time methods of Kohno et al. [J. Phys. Soc. Jpn. 75, 113706 (2006)]. We comment on the relationship between and isotropic-Stoner toy models of ferromagnetism and more realistic density-functional-theory models, and on the implications of these relationships for predictions of the ratio which plays a central role in domain-wall motion. Only for a single-parabolic-band isotropic-Stoner model with an exchange splitting that is small compared to the Fermi energy does approach 1. In addition, our microscopic formalism naturally incorporates the fluctuations needed in a nonzero-temperature description of the magnetization. We find that to first order in the applied electric field, the usual form of thermal fluctuations via a phenomenological stochastic magnetic field holds.- 18 June 2007
- Published by American Physical Society (APS) in Physical Review B
- Vol. 75 (21) , 214420
Functional Keldysh theory of spin torques
We present a microscopic treatment of current-induced torques and thermal fluctuations in itinerant ferromagnets based on a functional formulation of the Keldysh formalism. We find that the nonequilibrium magnetization dynamics is governed by a stochastic Landau-Lifschitz-Gilbert equation with spin-transfer torques. We calculate the Gilbert damping parameter and the nonadiabatic spin transfer torque parameter for a model ferromagnet. We find that , in agreement with the results obtained using imaginary-time methods of Kohno et al. [J. Phys. Soc. Jpn. 75, 113706 (2006)]. We comment on the relationship between and isotropic-Stoner toy models of ferromagnetism and more realistic density-functional-theory models, and on the implications of these relationships for predictions of the ratio which plays a central role in domain-wall motion. Only for a single-parabolic-band isotropic-Stoner model with an exchange splitting that is small compared to the Fermi energy does approach 1. In addition, our microscopic formalism naturally incorporates the fluctuations needed in a nonzero-temperature description of the magnetization. We find that to first order in the applied electric field, the usual form of thermal fluctuations via a phenomenological stochastic magnetic field holds.- 21 May 2007
- Published by American Physical Society (APS) in Physical Review B
- Vol. 75 (17)
Ab initiogiant magnetoresistance and current-induced torques inmultilayersWe report on an ab initio study of giant magnetoresistance (GMR) and current-induced torques (CITs) in trilayers that is based on nonequilibrium Green’s functions and spin-density functional theory. We find substantial GMR due primarily to a spin-dependent resonance centered at the interface and predict that the CITs are strong enough to switch the antiferromagnetic order parameter at current densities times smaller than switching current densities in ferromagnetic metal circuits. DOI: http://dx.doi.org/10.1103/PhysRevB.75.174428 © 2007 The American Physical Society- 21 May 2007
- Published by American Physical Society (APS) in Physical Review B
- Vol. 75 (17)
Ab initiogiant magnetoresistance and current-induced torques inmultilayersWe report on an ab initio study of giant magnetoresistance (GMR) and current-induced torques (CITs) in trilayers that is based on nonequilibrium Green’s functions and spin-density functional theory. We find substantial GMR due primarily to a spin-dependent resonance centered at the interface and predict that the CITs are strong enough to switch the antiferromagnetic order parameter at current densities times smaller than switching current densities in ferromagnetic metal circuits. DOI: http://dx.doi.org/10.1103/PhysRevB.75.174428 © 2007 The American Physical Society- 25 January 2007
- Published by American Physical Society (APS) in Physical Review B
- Vol. 75 (1) , 014433
Inelastic scattering in ferromagnetic and antiferromagnetic spin valves
We use a ferromagnetic voltage probe model to study the influence of inelastic scattering on giant magnetoresistance and current-induced torques in ferromagnetic and antiferromagnetic metal spin valves. The model is based on the Green’s function formulation of transport theory and represents spin-dependent and spin-independent inelastic scatterers by interior voltage probes that are constrained to carry respectively no charge current and no spin or charge current. We find that giant magnetoresistance and spin transfer torques in ferromagnetic metal spin valve structures survive arbitrarily strong spin-independent inelastic scattering, while the recently predicted analogous phenomena in antiferromagnetic metal spin valves are partially suppressed. We use toy-model numerical calculations to estimate spacer layer thickness requirements for room temperature operation of antiferromagnetic metal spin valves.
- 25 January 2007
- Published by American Physical Society (APS) in Physical Review B
- Vol. 75 (1) , 014433
Inelastic scattering in ferromagnetic and antiferromagnetic spin valves
We use a ferromagnetic voltage probe model to study the influence of inelastic scattering on giant magnetoresistance and current-induced torques in ferromagnetic and antiferromagnetic metal spin valves. The model is based on the Green’s function formulation of transport theory and represents spin-dependent and spin-independent inelastic scatterers by interior voltage probes that are constrained to carry respectively no charge current and no spin or charge current. We find that giant magnetoresistance and spin transfer torques in ferromagnetic metal spin valve structures survive arbitrarily strong spin-independent inelastic scattering, while the recently predicted analogous phenomena in antiferromagnetic metal spin valves are partially suppressed. We use toy-model numerical calculations to estimate spacer layer thickness requirements for room temperature operation of antiferromagnetic metal spin valves.
- Open Access
Ab-initio GMR and current-induced torques in Au/Cr multilayers
We report on an {\em ab-initio} study of giant magnetoresistance (GMR) and current-induced-torques (CITs) in Cr/Au multilayers that is based on non-equilibrium Green's functions and spin density functional theory. We find substantial GMR due primarily to a spin-dependent resonance centered at the Cr/Au interface and predict that the CITs are strong enough to switch the antiferromagnetic order parameter at current-densities $\sim 100$ times smaller than typical ferromagnetic metal circuit switching densities.Open AccessAb-initio GMR and current-induced torques in Au/Cr multilayers
We report on an {\em ab-initio} study of giant magnetoresistance (GMR) and current-induced-torques (CITs) in Cr/Au multilayers that is based on non-equilibrium Green's functions and spin density functional theory. We find substantial GMR due primarily to a spin-dependent resonance centered at the Cr/Au interface and predict that the CITs are strong enough to switch the antiferromagnetic order parameter at current-densities $\sim 100$ times smaller than typical ferromagnetic metal circuit switching densities. - Open Access
Current Induced Order Parameter Dynamics: Microscopic Theory Applied to Co/Cu/Co spin valves
Transport currents can alter alter order parameter dynamics and change steady states in superconductors, in ferromagnets, and in hybrid systems. In this article we present a scheme for fully microscopic evaluation of order parameter dynamics that is intended for application to nanoscale systems. The approach relies on time-dependent mean-field-theory, on an adiabatic approximation, and on the use of non-equilibrium Greens function (NEGF) theory to calculate the influence of a bias voltage across a system on its steady-state density matrix. We apply this scheme to examine the spin-transfer torques which drive magnetization dynamics in Co/Cu/Co spin-valve structures. Our microscopic torques are peaked near Co/Cu interfaces, in agreement with most previous pictures, but suprisingly act mainly on Co transition metal $d$-orbitals rather than on $s$-orbitals as generally supposed.
Open AccessCurrent Induced Order Parameter Dynamics: Microscopic Theory Applied to Co/Cu/Co spin valves
Transport currents can alter alter order parameter dynamics and change steady states in superconductors, in ferromagnets, and in hybrid systems. In this article we present a scheme for fully microscopic evaluation of order parameter dynamics that is intended for application to nanoscale systems. The approach relies on time-dependent mean-field-theory, on an adiabatic approximation, and on the use of non-equilibrium Greens function (NEGF) theory to calculate the influence of a bias voltage across a system on its steady-state density matrix. We apply this scheme to examine the spin-transfer torques which drive magnetization dynamics in Co/Cu/Co spin-valve structures. Our microscopic torques are peaked near Co/Cu interfaces, in agreement with most previous pictures, but suprisingly act mainly on Co transition metal $d$-orbitals rather than on $s$-orbitals as generally supposed.
- Open Access
Inelastic scattering in ferromagnetic and antiferromagnetic metal spintronics
We use a ferromagnetic voltage probe model to study the influence of inelastic scattering on giant magnetoresistance and current-induced torques in ferromagnetic and antiferromagnetic metal spin valves. The model is based on the Green's function formulation of transport theory and represents spin-dependent and spin-independent inelastic scatterers by interior voltage probes that are constrained to carry respectively no charge current and no spin or charge current. We find that giant magnetoresistance and spin transfer torques in ferromagnetic metal spin valve structures survive arbitrarily strong spin-independent inelastic scattering, while the recently predicted analogous phenomena in antiferromagnetic metal spin valves are partially suppressed. We use toy-model numerical calculations to estimate spacer layer thickness requirements for room temperature operation of antiferromagnetic metal spin valves.
Open AccessInelastic scattering in ferromagnetic and antiferromagnetic metal spintronics
We use a ferromagnetic voltage probe model to study the influence of inelastic scattering on giant magnetoresistance and current-induced torques in ferromagnetic and antiferromagnetic metal spin valves. The model is based on the Green's function formulation of transport theory and represents spin-dependent and spin-independent inelastic scatterers by interior voltage probes that are constrained to carry respectively no charge current and no spin or charge current. We find that giant magnetoresistance and spin transfer torques in ferromagnetic metal spin valve structures survive arbitrarily strong spin-independent inelastic scattering, while the recently predicted analogous phenomena in antiferromagnetic metal spin valves are partially suppressed. We use toy-model numerical calculations to estimate spacer layer thickness requirements for room temperature operation of antiferromagnetic metal spin valves.