1,310 research outputs found
Theory of spin and lattice wave dynamics excited by focused laser pulses
No full textWe develop a theory of spin wave dynamics excited by ultrafast focused laser pulses in a magnetic film. We take into account both the volume and surface spin wave modes in the presence of applied, dipolar and magnetic anisotropy fields and include the dependence on laser spot exposure size and magnetic damping. We show that the sound waves generated by local heating by an ultrafast focused laser pulse can excite a wide spectrum of spin waves (on top of a dominant magnon-phonon contribution). Good agreement with recent experiments supports the validity of the model.Accepted Author ManuscriptQN/Bauer Grou
Cavity optomagnonics: Manipulating magnetism by light
No full textWe discuss theoretically the coupling of magnetization and infrared photons in whispering gallery mode cavities.Casimir PhD Series, Delft-Leiden 2019-30QN/Bauer GroupQN/Theoretical Physic
Noncontact Spin Pumping by Microwave Evanescent Fields
No full textThe angular momentum of evanescent light fields has been studied in nano-optics and plasmonics but not in the microwave regime. Here we predict noncontact pumping of electron spin currents in conductors by the evanescent stray fields of excited magnetic nanostructures. The coherent transfer of the photon to the electron spin is proportional to the g factor, which is large in narrow gap semiconductors and surface states of topological insulators. The spin pumping current is chiral when the spin susceptibility displays singularities that indicate collective states. However, 1D systems with linear dispersion at the Fermi energy, such as metallic carbon nanotubes, are an exception since spin pumping is chiral even without interactions.QN/Bauer Grou
Spin pumping into two-dimensional electron systems
No full textWe study the spin current injected by spin pumping into single layer graphene and the two-dimensional electron gas (2DEG) with ferromagnetic contacts using scattering theory. The spin currents pumped into graphene are very distinct from that into the 2DEG since they are affected by Klein tunneling.QN/Bauer Grou
Damping of Magnetization Dynamics by Phonon Pumping
No full textWe theoretically investigate pumping of phonons by the dynamics of a magnetic film into a nonmagnetic contact. The enhanced damping due to the loss of energy and angular momentum shows interference patterns as a function of the resonance frequency and magnetic film thickness that cannot be described by viscous ("Gilbert") damping. The phonon pumping depends on the magnetization direction as well as geometrical and material parameters and is observable, e.g., in thin films of yttrium iron garnet on a thick dielectric substrate.QN/Bauer Grou
Energy repartition in the nonequilibrium steady state
No full textThe concept of temperature in nonequilibrium thermodynamics is an outstanding theoretical issue. We propose an energy repartition principle that leads to a spectral (mode-dependent) temperature in steady-state nonequilibrium systems. The general concepts are illustrated by analytic solutions of the classical Heisenberg spin chain connected to Langevin heat reservoirs with arbitrary temperature profiles. Gradients of external magnetic fields are shown to localize spin waves in a Wannier-Zeemann fashion, while magnon interactions renormalize the spectral temperature. Our generic results are applicable to other thermodynamic systems such as Newtonian liquids, elastic solids, and Josephson junctions.QN/Bauer Grou
Coherent pumping of high-momentum magnons by light
No full textWe propose and model a method to excite a large number of coherent magnons with high momentum in optical cavities. This is achieved by two counterpropagating optical modes that are detuned by the frequency of a selected magnon, similar to stimulated Raman scattering. In submillimeter-size yttrium iron garnet spheres, a milliwatt laser input power generates 106-108 coherent magnons. The large magnon population enhances Brillouin light scattering, a probe suitable to access their quantum properties.QN/Bauer GroupQN/Blanter Grou
Thermal spin dynamics of yttrium iron garnet
No full textThe magnetic insulator yttrium iron garnet can be grown with near perfection and is therefore and ideal conduit for spin currents. It is a complex material with 20 magnetic moments in the unit cell. In spite of being a ferrimagnet, YIG is almost always modeled as a simple ferromagnet with a single spin wave mode. We use the method of atomistic spin dynamics to study the temperature evolution of the full spin wave spectrum, in quantitative agreement with neutron scattering experiments. The antiferromagnetic or optical mode is found to suppress the spin Seebeck effect at room temperature and beyond due to thermally pumped spin currents with opposite polarization to the ferromagnetic mode.QN/Bauer Grou
Optical Cooling of Magnons
No full textInelastic scattering of light by spin waves generates an energy flow between the light and magnetization fields, a process that can be enhanced and controlled by concentrating the light in magneto-optical resonators. Here, we model the cooling of a sphere made of a magnetic insulator, such as yttrium iron garnet, using a monochromatic laser source. When the magnon lifetimes are much larger than the optical ones, we can treat the latter as a Markovian bath for magnons. The steady-state magnons are canonically distributed with a temperature that is controlled by the light intensity. We predict that such a cooling process can significantly reduce the temperature of the magnetic order within current technology.QN/Bauer GroupQN/Blanter Grou
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