arXiv subjects

Yaroslav Tserkovnyak

Publications and source records attributed to Yaroslav Tserkovnyak.

At least 181 records · Page 10Linked to original sources

arXiv2010

Scattering Theory of Charge-Current Induced Magnetization Dynamics

In ferromagnets, charge currents can excite magnons via the spin-orbit coupling. We develop a novel and general scattering theory of charge current induced macrospin magnetization torques in normal metal$|$ferromagnet$|$normal metal layers. We apply the formalism to a dirty GaAs$|$(Ga,Mn)As$|$GaAs system. By computing the charge current induced magnetization torques and solving the Landau-Lifshitz-Gilbert equation, we find magnetization switching for current densities as low as $ 5\times 10^{6}$~A/cm$^2$. Our results are in agreement with a recent experimental observation of charge-current induced magnetization switching in (Ga,Mn)As.

cond-mat.mes-hall↗

arXiv2010

Dissipative dynamics of magnetic solitons in metals

Soliton dynamics in spin-textured metals generate electrical currents, which produce backaction through spin torques. We modify the Landau-Lifshitz-Gilbert equation and the corresponding solitonic equations of motion to include such higher-order texture effects. We also find a quasistatic equation for the induced electrochemical potential, which needs to be solved for self-consistently, in the incompressible limit. As an example, we consider the orbital motion of a vortex in a point-contact spin valve, and discuss modifications of orbit radius, frequency, and dissipation power.

cond-mat.mes-hall↗

arXiv2010

Nanoscale Magnetic Heat Pumps and Engines

We present the linear response matrix for a sliding domain wall in a rotatable magnetic nanowire, which is driven out of equilibrium by temperature and voltage bias, mechanical torque, and magnetic field. An expression for heat-current induced domain wall motion is derived. Application of Onsager's reciprocity relation leads to a unified description of the Barnett and Einstein-de Haas effects as well as spin-dependent thermoelectric properties. We envisage various heat pumps and engines, such as coolers driven by magnetic fields or mechanical rotation as well as nanoscale motors that convert temperature gradients into useful work. All parameters (with the exception of mechanical friction) can be computed microscopically by the scattering theory of transport.

cond-mat.mes-hall↗

arXiv2009

Hydrodynamic theory of coupled current and magnetization dynamics in spin-textured ferromagnets

We develop the hydrodynamical theory of collinear spin currents coupled to magnetization dynamics in metallic ferromagnets. The collective spin density couples to the spin current through a U(1) Berry-phase gauge field determined by the local texture and dynamics of the magnetization. We determine phenomenologically the dissipative corrections to the equation of motion for the electronic current, which consist of a dissipative spin-motive force generated by magnetization dynamics and a magnetic texture-dependent resistivity tensor. The reciprocal dissipative, adiabatic spin torque on the magnetic texture follows from the Onsager principle. We investigate the effects of thermal fluctuations and find that electronic dynamics contribute to a nonlocal Gilbert damping tensor in the Landau-Lifshitz-Gilbert equation for the magnetization. Several simple examples, including magnetic vortices, helices, and spirals, are analyzed in detail to demonstrate general principles.

cond-mat.mes-hall↗

arXiv2009

Magnetocaloritronic nanomachines

We introduce and study a magnetocaloritronic circuit element based on a domain wall that can move under applied voltage, magnetic field and temperature gradient. We draw analogies between the Carnot machines and possible devices employing such circuit element. We further point out the parallels between the operational principles of thermoelectric and magnetocaloritronic cooling and power generation and also introduce a magnetocaloritronic figure of merit. Even though the magnetocaloritronic figure of merit turns out to be very small for transition-metal based magnets, we speculate that larger numbers may be expected in ferromagnetic insulators.

cond-mat.mes-hall↗

arXiv2009

Barnett Effect in Thin Magnetic Films and Nanostructures

The Barnett effect refers to the magnetization induced by rotation of a demagnetized ferromagnet. We describe the location and stability of stationary states in rotating nanostructures using the Landau-Lifshitz-Gilbert equation. The conditions for an experimental observation of the Barnett effect in different materials and sample geometries are discussed.

cond-mat.mes-hall↗

arXiv2009

Tuning odd triplet superconductivity by spin pumping

We study proximity effect in diffusive ferromagnet/normal-metal/superconductor junction with precessing magnetization of the ferromagnet. We find that the odd-frequency pairing induced in the normal metal is modified by spin pumping from the ferromagnet and hence can be tuned by changing the precessional frequency. At the frequency corresponding to twice the superconducting gap, the odd-frequency pairing is strongly enhanced. We find a crossover from the even- to the odd-frequency superconductivity in the normal metal by tuning the precessional frequency. This gives a clearcut signature of the odd-frequency superconductivity observable by scanning tunneling microscopy. According to the pairing symmetries in the normal metal, we find a crossover from the gap to the peak structure in the tunneling conductance between the normal metal and a scanning tunneling microscope tip.

cond-mat.supr-con↗

arXiv2009

Thermoelectric spin transfer in textured magnets

We study charge and energy transport in a quasi-1D magnetic wire in the presence of magnetic textures. The energy flows can be expressed in a fashion similar to charge currents, leading to new energy-current induced spin torques. In analogy to charge currents, we can identify two reciprocal effects: spin-transfer torque on the magnetic order parameter induced by energy current and the Berry-phase gauge field induced energy flow. In addition, we phenomenologically introduce new $β-$like viscous coupling between magnetic dynamics and energy current into the LLG equation, which originates from spin mistracking of the magnetic order. We conclude that the new viscous term should be important for the thermally induced domain wall motion. We study the interplay between charge and energy currents and find that many of the effects of texture motion on the charge currents can be replicated with respect to energy currents. For example, the moving texture can lead to energy flows which is an analogue of the electromotive force in case of charge currents. We suggest a realization of cooling effect by magnetic texture dynamics.

cond-mat.mes-hall↗

arXiv2009

Aharonov-Casher Effect in Wigner Crystal Exchange Interactions

We theoretically study the effects of spin-orbit coupling on spin exchange in a low-density Wigner crystal. In addition to the familiar antiferromagnetic Heisenberg exchange, we find general anisotropic interactions in spin space if the exchange paths allowed by the crystal structure form loops in real space. In particular, it is shown that the two-electron exchange interaction can acquire ferromagnetic character.

cond-mat.mes-hall↗

arXiv2009

Transverse spin diffusion in ferromagnets

We discuss the dissipative diffusion-type term of the form $\mathbf{m}\times\nabla^2\partial_t\mathbf{m}$ in the phenomenological Landau-Lifshitz equation of ferromagnetic precession, which describes enhanced Gilbert damping of finite-momentum spin waves. This term arises physically from itinerant-electron spin flows through a perturbed ferromagnetic configuration and can be understood to originate in the ferromagnetic spin pumping in the continuum limit. We develop a general phenomenology as well as provide microscopic theory for the Stoner and s-d models of ferromagnetism, taking into account disorder and electron-electron scattering. The latter is manifested in our problem through the Coulomb drag between the spin bands. The spin diffusion is identified in terms of the transverse spin conductivity, in analogy with the Einstein relation in the kinetic theory.

cond-mat.mes-hall↗

arXiv2009

Noise and dissipation in magnetoelectronic nanostructures

We study the coupled current and magnetization noise in magnetic nanostructures by magnetoelectronic circuit theory. Spin current fluctuations, which depend on the magnetic configuration, are found to be an important source of magnetization noise and damping in thinly layered systems. The enhanced magnetization fluctuations in spin valves can be directly measured by their effect on the resistance noise.

cond-mat.mes-hall↗

arXiv2009

Spin-selective localization due to intrinsic spin-orbit coupling

We study spin-dependent diffusive transport in the presence of a tunable spin-orbit (SO) interaction in a two-dimensional electron system. The spin precession of an electron in the SO coupling field is expressed in terms of a covariant curvature, affecting the quantum interference between different electronic trajectories. Controlling this curvature field by modulating the SO coupling strength and its gradients by, e.g., electric or elastic means, opens intriguing possibilities for exploring spin-selective localization physics. In particular, applying a weak magnetic field allows the control of the electron localization independently for two spin directions, with the spin-quantization axis that could be "engineered" by appropriate SO interaction gradients.

cond-mat.mes-hall↗

arXiv2009

Transport theory for disordered multiple-band systems: Anomalous Hall effect and anisotropic magnetoresistance

We present a study of transport in multiple-band non-interacting Fermi metallic systems based on the Keldysh formalism, taking into account the effects of Berry curvature due to spin-orbit coupling. We apply this formalism to a Rashba 2DEG ferromagnet and calculate the anomalous Hall effect (AHE) and anisotropic magnetoresistance (AMR). The numerical calculations reproduce analytical results in the metallic regime revealing the crossover between the skew scattering mechanism dominating in the clean systems and intrinsic mechanism dominating in the moderately dirty systems. As we increase the disorder further, the AHE starts to diminish due to the spectral broadening of the quasiparticles. Although for certain parameters this reduction of the AHE can be approximated as $σ_{xy}\thicksimσ_{xx}^φ$ with $φ$ varying around 1.6, this is found not to be true in general as $σ_{xy}$ can go through a change in sign as a function of disorder strength in some cases. The reduction region in which the quasiparticle approximation is meaningful is relatively narrow; therefore, a theory with a wider range of applicability is called for. By considering the higher order skew scattering processes, we resolve some discrepancies between the AHE results obtained by using the Keldysh, Kubo and Boltzmann approaches. We also show that similar higher order processes are important for the AMR when the nonvertex and vertex parts cancel each other. We calculate the AMR in anisotropic systems properly taking into account the anisotropy of the non-equilibrium distribution function. These calculations confirm recent findings on the unreliability of common approximations to the Boltzmann equation.

cond-mat.mes-hall↗

arXiv2009

Theory of spin magnetohydrodynamics

We develop a phenomenological hydrodynamic theory of coherent magnetic precession coupled to electric currents. Exchange interaction between electron spin and collective magnetic texture produces two reciprocal effects: spin-transfer torque on the magnetic order parameter and the Berry-phase gauge field experienced by the itinerant electrons. The dissipative processes are governed by three coefficients: the ohmic resistance, Gilbert damping of the magnetization, and the "beta coefficient" describing viscous coupling between magnetic dynamics and electric current, which stems from spin mistracking of the magnetic order. We develop general magnetohydrodynamic equations and discuss the net dissipation produced by the coupled dynamics. The latter in particular allows us to determine a lower bound on the magnetic-texture resistivity.

cond-mat.mes-hall↗

arXiv2008

Spin-charge separation in a strongly correlated spin-polarized chain

We combine the first-quantized path-integral formalism and bosonization to develop a phenomenological theory for spin-charge coupled dynamics in one-dimensional (1D) ferromagnetic systems with strong interparticle repulsion, at low temperatures. We assume an effective spin-charge separation and retain the standard Luttinger-liquid plasmon branch, which is explicitly coupled to a ferromagnetic spin-wave texture with a quadratic dispersion. The dynamic spin structure severely suppresses the plasmon peak in the single-particle propagator, in both fermionic and bosonic systems. Our analysis provides an effective theory for the new universality class of 1D ferromagnetic systems, capturing both the trapped spin and propagating spin-wave regimes of the long-time behavior.

cond-mat.str-el↗

arXiv2008

Tunnel-barrier-enhanced dc voltage signals induced by magnetization dynamics in magnetic tunnel junctions

We theoretically study the recently observed tunnel-barrier-enhanced dc voltage signals generated by magnetization precession in magnetic tunnel junctions. While the spin pumping is suppressed by the high tunneling impedance, two complimentary processes are predicted to result in a sizable voltage generation in ferromagnet (F)|insulator (I)|normal-metal (N) and F|I|F junctions, with one ferromagnet being resonantly excited. Magnetic dynamics in F|I|F systems induces a robust charge pumping, translating into voltage in open circuits. In addition, dynamics in a single ferromagnetic layer develops longitudinal spin accumulation inside the ferromagnet. A tunnel barrier then acts as a nonintrusive probe that converts the spin accumulation into a measurable voltage. Neither of the proposed mechanisms suffers from spin relaxation, which is typically fast on the scale of the exponentially slow tunneling rates. The longitudinal spin-accumulation buildup, however, is very sensitive to the phenomenological ingredients of the spin-relaxation picture.

cond-mat.mes-hall↗

arXiv2008

Scattering Theory of Gilbert Damping

The magnetization dynamics of a single domain ferromagnet in contact with a thermal bath is studied by scattering theory. We recover the Landau-Liftshitz-Gilbert equation and express the effective fields and Gilbert damping tensor in terms of the scattering matrix. Dissipation of magnetic energy equals energy current pumped out of the system by the time-dependent magnetization, with separable spin-relaxation induced bulk and spin-pumping generated interface contributions. In linear response, our scattering theory for the Gilbert damping tensor is equivalent with the Kubo formalism.

cond-mat.mes-hall↗

arXiv2008

Electron Transport Driven by Nonequilibrium Magnetic Textures

Spin-polarized electron transport driven by inhomogeneous magnetic dynamics is discussed in the limit of a large exchange coupling. Electron spins rigidly following the time-dependent magnetic profile experience spin-dependent fictitious electric and magnetic fields. We show that the electric field acquires important corrections due to spin dephasing, when one relaxes the spin-projection approximation. Furthermore, spin-flip scattering between the spin bands needs to be taken into account in order to calculate voltages and spin accumulations induced by the magnetic dynamics. A phenomenological approach based on the Onsager reciprocity principle is developed, which allows us to capture the effect of spin dephasing and make a connection to the well studied problem of current-driven magnetic dynamics. A number of results that recently appeared in the literature are related and generalized.

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