354 research outputs found
Stable and fast semi-implicit integration of the stochastic Landau-Lifshitz equation
We propose new semi-implicit numerical methods for the integration of the
stochastic Landau-Lifshitz equation with built-in angular momentum
conservation. The performance of the proposed integrators is tested on the 1D
Heisenberg chain. For this system, our schemes show better stability properties
and allow us to use considerably larger time steps than standard explicit
methods. At the same time, these semi-implicit schemes are also of comparable
accuracy to and computationally much cheaper than the standard midpoint
implicit method. The results are of key importance for atomistic spin dynamics
simulations and the study of spin dynamics beyond the macro spin approximation.Comment: 24 pages, 5 figure
Nonlinear effects in the propagation of optically generated magnetostatic volume mode spin waves
Recent experimental work has demonstrated optical control of spin wave
emission by tuning the shape of the optical pulse (Satoh et al.\ Nature
Photonics, 6, 662 (2012)). We reproduce these results and extend the scope of
the control by investigating nonlinear effects for large amplitude excitations.
We observe an accumulation of spin wave power at the center of the initial
excitation combined with short-wavelength spin waves. These kind of nonlinear
effects have not been observed in earlier work on nonlinearities of spin waves.
Our observations pave the way for the manipulation of magnetic structures at a
smaller scale than the beam focus, for instance in devices with all-optical
control of magnetism.Comment: Added new figures to further illustrate the nonlinear effects to show
time evolution and spectral flow. Added references. Changed perspective on
nonlinear effects w.r.t. applicability of NSE. Added acknowledgemen
High Field Anomalies of Equilibrium and Ultrafast Magnetism in Rare-Earth-Transition Metal Ferrimagnets
Magneto-optical spectroscopy in fields up to 30 Tesla reveals anomalies in
the equilibrium and ultrafast magnetic properties of the ferrimagnetic
rare-earth-transition metal alloy TbFeCo. In particular, in the vicinity of the
magnetization compensation temperature, each of the magnetizations of the
antiferromagnetically coupled Tb and FeCo sublattices show triple hysteresis
loops. Contrary to state-of-the-art theory, which explains such loops by sample
inhomogeneities, here we show that they are an intrinsic property of the
rare-earth ferrimagnets. Assuming that the rare-earth ions are paramagnetic and
have a non-zero orbital momentum in the ground state and, therefore, a large
magnetic anisotropy, we are able to reproduce the experimentally observed
behavior in equilibrium. The same theory is also able to describe the
experimentally observed critical slowdown of the spin dynamics in the vicinity
of the magnetization compensation temperature, emphasizing the role played by
the orbital momentum in static and ultrafast magnetism of ferrimagnets
Infrared studies of a La_(0.67)Ca_(0.33)MnO_3 single crystal: Optical magnetoconductivity in a half-metallic ferromagnet
The infrared reflectivity of a La_(0.67)Ca_(0.33)MnO_3 single crystal is studied over a broad range of temperatures (78–340 K), magnetic fields (0–16 T), and wave numbers (20–9000cm^(-1)). The optical conductivity gradually changes from a Drude-like behavior to a broad peak feature near 5000cm-1 in the ferromagnetic state below the Curie temperature T_C=307K. Various features of the optical conductivity bear striking resemblance to recent theoretical predictions based on the interplay between the double exchange interaction and the Jahn-Teller electron-phonon coupling. A large optical magnetoconductivity is observed near T_C
Laser-driven quantum magnonics and THz dynamics of the order parameter in antiferromagnets
The impulsive generation of two-magnon modes in antiferromagnets by
femtosecond optical pulses, so-called femto-nanomagnons, leads to coherent
longitudinal oscillations of the antiferromagnetic order parameter that cannot
be described by a thermodynamic Landau-Lifshitz approach. We argue that this
dynamics is triggered as a result of a laser-induced modification of the
exchange interaction. In order to describe the oscillations we have formulated
a quantum mechanical description in terms of magnon pair operators and coherent
states. Such an approach allowed us to} derive an effective macroscopic
equation of motion for the temporal evolution of the antiferromagnetic order
parameter. An implication of the latter is that the photo-induced spin dynamics
represents a macroscopic entanglement of pairs of magnons with femtosecond
period and nanometer wavelength. By performing magneto-optical pump-probe
experiments with 10 femtosecond resolution in the cubic KNiF and the
uniaxial KNiF collinear Heisenberg antiferromagnets, we observed
coherent oscillations at the frequency of 22 THz and 16 THz, respectively. The
detected frequencies as a function of the temperature ideally fit the
two-magnon excitation up to the N\'eel point. The experimental signals are
described as dynamics of magnetic linear dichroism due to longitudinal
oscillations of the antiferromagnetic vector.Comment: 25 pages, 10 figure
Infrared Studies of a La_{0.67}Ca_{0.33}MnO_3 Single Crystal: Optical Magnetoconductivity in a Half-Metallic Ferromagnet
The infrared reflectivity of a single crystal
is studied over a broad range of temperatures (78-340 K), magnetic fields (0-16
T), and wavenumbers (20-9000 cm). The optical conductivity gradually
changes from a Drude-like behavior to a broad peak feature near 5000 cm
in the ferromagnetic state below the Curie temperature . Various
features of the optical conductivity bear striking resemblance to recent
theoretical predictions based on the interplay between the double exchange
interaction and the Jahn-Teller electron-phonon coupling. A large optical
magnetoconductivity is observed near .Comment: 4 pages, 4 figures, Latex, PostScript; The 7th Joint MMM-Intermag
Conference,San Francisco, January 6-9, 1998; The Int. Conf. on Strongly
Correlated Electron Systems, Paris, July 15-18,199
The Impact of Music on Stress Biomarkers:Protocol of a Substudy of the Cluster-Randomized Controlled Trial Music Interventions for Dementia and Depression in ELderly Care (MIDDEL)
Recently, a large cluster-randomized controlled trial was designed-Music Interventions for Dementia and Depression in ELderly care (MIDDEL)-to assess the effectiveness of music interventions on depression in care home residents with dementia (ClinicalTrials.gov NCT03496675). To understand the pathophysiological mechanisms, we observed the effect of repeated music interventions on stress in this population since chronic stress was associated with depression and an increased risk for dementia. An exploratory study was designed to assess: (1) changes in hair cortisol concentrations as an indicator of longer-term stress; (2) whether baseline stress is a predictor of therapy outcome; (3) pre- and post-treatment effects on salivary α-amylase and cortisol response as an indicator of immediate stress in 180-200 care home residents with dementia and depressive symptoms who partake in the MIDDEL trial. Insights into mediatory effects of stress to explain the effect of music interventions will be gained. Hair cortisol concentrations were assessed at baseline and at 3, 6, and 12 months along with the Perceived Stress Scale. Salivary α-amylase and cortisol concentrations were assessed at 1, 3, and 6 months. Saliva was collected just before a session and 15 and 60 min after a session, along with a stress Visual Analogue Scale.</p
Phase-transitions in high magnetic-fields
Contains fulltext :
92721.pdf (publisher's version ) (Open Access
Ultrafast optical modification of exchange interactions in iron oxides
Ultrafast non-thermal manipulation of magnetization by light relies on either indirect coupling of the electric field component of the light with spins via spin-orbit interaction or direct coupling between the magnetic field component and spins. Here we propose a scenario for coupling between the electric field of light and spins via optical modification of the exchange interaction, one of the strongest quantum effects with strength of 10(3) Tesla. We demonstrate that this isotropic opto-magnetic effect, which can be called inverse magneto-refraction, is allowed in a material of any symmetry. Its existence is corroborated by the experimental observation of terahertz emission by spin resonances optically excited in a broad class of iron oxides with a canted spin configuration. From its strength we estimate that a sub-picosecond modification of the exchange interaction by laser pulses with fluence of about 1 mJ cm(-2) acts as a pulsed effective magnetic field of 0.01 Tesla.European Commission’s 7th Framework Program (FP7/2007–2013)EPSRCNetherlands Organization for Scientific Research (NWO)Foundation for Fundamental Research on Matter (FOM)European Research CouncilRussian Ministry of Education and ScienceRFBR-NSFC projectBureau of International CooperationNSFC projectNSFC-NWOEU Seventh Framework ProgramNWO by a Rubicon grantEuropean Commission (FP7-ICT-2013-613024–GRASP
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