A method for the calculations of the Gilbert damping parameter alpha is presented, which, based on the linear response formalism, has been implemented within the fully relativistic ...Korringa-Kohn-Rostoker band structure method in combination with the coherent potential approximation alloy theory. To account for thermal displacements of atoms as a scattering mechanism, an alloy-analogy model is introduced. This allows the determination of alpha for various types of materials, such as elemental magnetic systems and ordered magnetic compounds at finite temperature, as well as for disordered magnetic alloys at T = 0 K and above. The effects of spin-orbit coupling, chemical- and temperature-induced structural disorder, are analyzed. Calculations have been performed for the 3d transition metals bcc Fe, hcp Co, and fcc Ni; their binary alloys bcc Fe sub(1-x) Co sub(x), fcc Ni sub(1-x) Fe sub(x), fcc Ni sub(1-x)Co sub(x) and bcc Fe sub(1-x)V sub(x); and for 5d impurities in transition-metal alloys. All results are in satisfying agreement with experiment.
Terahertz magnetic fields with amplitudes of up to 0.4 Tesla drive magnon resonances in nickel oxide while the induced dynamics is recorded by femtosecond magneto-optical probing. We observe distinct ...spin-mediated optical nonlinearities, including oscillations at the second harmonic of the 1 THz magnon mode. The latter originate from coherent dynamics of the longitudinal component of the antiferromagnetic order parameter, which are probed by magneto-optical effects of second order in the spin deflection. These observations allow us to dynamically disentangle electronic from lattice-related contributions to magnetic linear birefringence and dichroism-information so far only accessible by ultrafast THz spin control. The nonlinearities discussed here foreshadow physics that will become essential in future subcycle spin switching.
Unique features of the Gilbert damping in magnetic multilayers were investigated by ferromagnetic resonance (FMR) using magnetic single and double layer structures prepared by molecular beam epitaxy. ...The FMR linewidth for the Fe films in the double layer structures was larger than the FMR linewidth in the single Fe films having the same thickness. The additional FMR linewidth scaled inversely with the film thickness, and increased linearly with increasing microwave frequency. These results demonstrate that a transfer of electron angular momentum between the magnetic layers leads to additional relaxation torques.
Terahertz near fields of gold metamaterials resonant at a frequency of 0.88 THz allow us to enter an extreme limit of nonperturbative ultrafast terahertz electronics: Fields reaching a ponderomotive ...energy in the keV range are exploited to drive nondestructive, quasistatic interband tunneling and impact ionization in undoped bulk GaAs, injecting electron-hole plasmas with densities in excess of 10^{19} cm^{-3}. This process causes bright luminescence at energies up to 0.5 eV above the band gap and induces a complete switch-off of the metamaterial resonance accompanied by self-amplitude-modulation of transmitted few-cycle terahertz transients. Our results pave the way towards highly nonlinear terahertz optics and optoelectronic nanocircuitry with subpicosecond switching times.
All-electrical spin-wave spectroscopy, Brillouin light scattering, as well as the magneto-optical Kerr effect are combined to study spin-wave propagation through a magnetic antidot lattice ...nanopatterned into a Ni(80)Fe(20) thin film. The propagation velocities and, in particular, the relaxation are found to depend characteristically on the applied in-plane magnetic field. We explain the observed anisotropies by magnetic field-controlled spin-wave guiding in a network of interconnected nanowires which takes place over distances of up to 20 μm.
Doping Ni80Fe20 by heavy rare earth atoms alters the magnetic relaxation properties of this material drastically. We show that this effect can be well explained by the slow relaxing impurity ...mechanism. This process is a consequence of the anisotropy of the on site exchange interaction between the 4f magnetic moments and the conduction band. As expected from this model the magnitude of the damping effect scales with the anisotropy of the exchange interaction and increases by an order of magnitude at low temperatures. In addition, our measurements allow us to determine the relaxation time of the 4f electrons as a function of temperature.
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