85 research outputs found
Abstract for an Invited Paper for the MAR06 Meeting of The American Physical Society Ultrafast coherent control of Spin-and magnetization dynamics
The manipulating of the electron spin is not only relevant for magnetic storage but may also lead to the development of novel electronic devices with new characteristics (so-called spintronics). Therefore, the investigations of the physical mechanisms underlying the manipulation of electron spin in ferromagnets, semiconductors and hybrid ferromagnet/semiconductor structures constitute at present an exciting area of research. Due to the fact that in antiferromagnets no angular momentum is associated with the order parameter, spin dynamics in these materials is intrinsically much faster than in ferromagnets, expanding the area of spin-dynamics even more [1] . Femto-second laser excitation opens the way to excite magnetic systems on a time scale much shorter than fundamental time scales such as spin-lattice relaxation or precession times. This has already lead to surprising and exciting results like changes in magnetization on a sub-picoscond time scale [2] . Fs laser pulses can also be used to generate short magnetic field pulses, that allow coherent control of the magnetization dynamics [3] . Recent progress in this area will be discussed, demonstrating in particular the use of time resolved magneto-optical methods to investigate the static and dynamic properties of magnetically ordered structures and the possibility of direct spin manipulation with optical fields [4,5
Generation of single skyrmions by picosecond magnetic field pulses
We numerically demonstrate an ultrafast method to create
skyrmions in a ferromagnetic sample by applying a
picosecond (effective) magnetic field pulse in the presence of
Dzyaloshinskii-Moriya interaction. For small samples the applied magnetic field
pulse could be either spatially uniform or nonuniform while for large samples a
nonuniform and localized field is more effective. We examine the phase diagram
of pulse width and amplitude for the nucleation. Our finding could ultimately
be used to design future skyrmion-based devices.Comment: 4.5 pages+Supplemental Materia
Switching of chiral magnetic skyrmions by picosecond magnetic field pulses via transient topological states
Magnetic chiral skyrmions are vortex like spin structures that appear as
stable or meta-stable states in magnetic materials due to the interplay between
the symmetric and antisymmetric exchange interactions, applied magnetic field
and/or uniaxial anisotropy. Their small size and internal stability make them
prospective objects for data storage but for this, the controlled switching
between skyrmion states of opposite polarity and topological charge is
essential. Here we present a study of magnetic skyrmion switching by an applied
magnetic field pulse based on a discrete model of classical spins and atomistic
spin dynamics. We found a finite range of coupling parameters corresponding to
the coexistence of two degenerate isolated skyrmions characterized by mutually
inverted spin structures with opposite polarity and topological charge. We
demonstrate how for a wide range of material parameters a short inclined
magnetic field pulse can initiate the reliable switching between these states
at GHz rates. Detailed analysis of the switching mechanism revealed the complex
path of the system accompanied with the excitation of a chiral-achiral meron
pair and the formation of an achiral skyrmion
Excitation of magnetic precession in bismuth iron garnet via a polarization-independent impulsive photomagnetic effect
A polarization-independent, nonthermal optical effect on the magnetization in
bismuth iron garnet is found, in addition to the circular
polarization-dependent inverse Faraday effect and the linear
polarization-dependent photoinduced magnetic anisotropy. Its impulsive
character is demonstrated by the field dependence of the amplitude of the
resulting precession, which cannot be explained by a long-living photo or
heat-induced anisotropy.Comment: 12 pages, 3 Figure
Frequency and wavenumber selective excitation of spin waves through coherent energy transfer from elastic waves
Using spin-wave tomography (SWaT), we have investigated the excitation and
the propagation dynamics of optically-excited magnetoelastic waves, i.e.
hybridized modes of spin waves and elastic waves, in a garnet film. By using
time-resolved SWaT, we reveal the excitation dynamics of magnetoelastic waves
through coherent-energy transfer between optically-excited pure-elastic waves
and spin waves via magnetoelastic coupling. This process realizes frequency and
wavenumber selective excitation of spin waves at the crossing of the dispersion
relations of spin waves and elastic waves. Finally, we demonstrate that the
excitation mechanism of the optically-excited pure-elastic waves, which are the
source of the observed magnetoelastic waves, is dissipative in nature.Comment: 5 pages, 4 figure
Nonlinear surface magneto-plasmonics in Kretschmann multilayers
The nonlinear magneto-plasmonics aims to utilize plasmonic excitations to
control the mechanisms and taylor the efficiencies of the non-linear light
frequency conversion at the nanoscale. We investigate the mechanisms of
magnetic second harmonic generation in hybrid gold-cobalt-silver multilayer
structures, which support propagating surface plasmon polaritons at both
fundamental and second harmonic frequencies. Using magneto-optical spectroscopy
in Kretschmann geometry, we show that the huge magneto-optical modulation of
the second harmonic intensity is dominated by the excitation of surface plasmon
polaritons at the second harmonic frequency, as shown by tuning the optical
wavelength over the spectral region of strong plasmonic dispersion. Our
proof-of-principle experiment highlights bright prospects of nonlinear
magneto-plasmonics and contributes to the general understanding of the
nonlinear optics of magnetic surfaces and interfaces.Comment: Main Manuscript: 5 pages, 3 figures. Supplementary Information: 10
pages, 7 figure
All-thermal switching of amorphous Gd-Fe alloys: analysis of structural properties and magnetization dynamics
In recent years, there has been an intense interest in understanding the
microscopic mechanism of thermally induced magnetization switching driven by a
femtosecond laser pulse. Most of the effort has been dedicated to periodic
crystalline structures while the amorphous counterparts have been less studied.
By using a multiscale approach, i.e. first-principles density functional theory
combined with atomistic spin dynamics, we report here on the very intricate
structural and magnetic nature of amorphous Gd-Fe alloys for a wide range of Gd
and Fe atomic concentrations at the nanoscale level. Both structural and
dynamical properties of Gd-Fe alloys reported in this work are in good
agreement with previous experiments. We calculated the dynamic behavior of
homogeneous and inhomogeneous amorphous Gd-Fe alloys and their response under
the influence of a femtosecond laser pulse. In the homogeneous sample, the Fe
sublattice switches its magnetization before the Gd one. However, the temporal
sequence of the switching of the two sublattices is reversed in the
inhomogeneous sample. We propose a possible explanation based on a mechanism
driven by a combination of the Dzyaloshiskii-Moriya interaction and exchange
frustration, modeled by an antiferromagnetic second-neighbour exchange
interaction between Gd atoms in the Gd-rich region. We also report on the
influence of laser fluence and damping effects in the all-thermal switching.Comment: Accepted in Physical Review B as a regular article. It contains 14
pages and 14 figure
Ultrafast thermally induced magnetic switching in synthetic ferrimagnets
Synthetic ferrimagnets are composite magnetic structures formed from two or more anti-ferromagnetically coupled magnetic sublattices with different magnetic moments. Here, we report on atomistic spin simulations of the laser-induced magnetization dynamics on such synthetic ferrimagnets and demonstrate that the application of ultrashort laser pulses leads to sub-picosecond magnetization dynamics and all-optical switching in a similar manner as in ferrimagnetic alloys. Moreover, we present the essential material properties for successful laser-induced switching, demonstrating the feasibility of using a synthetic ferrimagnet as a high density magnetic storage element without the need of a write field
- …