1,325 research outputs found
Spatially resolved observation of uniform precession modes in spin-valve systems
Using time-resolved photoemission electron microscopy the excitation of
uniform precession modes in individual domains of a weakly coupled spin-valve
system has been studied. A coupling dependence of the precession frequencies
has been found that can be reasonably well understood on the basis of a
macrospin model. By tuning the frequency of the excitation source the uniform
precession modes are excited in a resonant way.Comment: This article has been accepted by Journal of Applied Physics. After
it is published, it will be found at http://jap.aip.or
Ultrafast optical control of magnetization in EuO thin films
All-optical pump-probe detection of magnetization precession has been
performed for ferromagnetic EuO thin films at 10 K. We demonstrate that the
circularly-polarized light can be used to control the magnetization precession
on an ultrafast time scale. This takes place within the 100 fs duration of a
single laser pulse, through combined contribution from two nonthermal
photomagnetic effects, i.e., enhancement of the magnetization and an inverse
Faraday effect. From the magnetic field dependences of the frequency and the
Gilbert damping parameter, the intrinsic Gilbert damping coefficient is
evaluated to be {\alpha} \approx 3\times10^-3.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev.
The structure of the Au(111)/methylthiolate interface : new insights from near-edge X-ray absorption spectroscopy and X-ray standing waves
The local structure of the Au(111)([square root of]3×[square root of]3)R30°-methylthiolate surface phase has been investigated by S K-edge near-edge s-ray absorption fine structure (NEXAFS) both experimentally and theoretically and by experimental normal-incidence x-ray standing waves (NIXSW) at both the C and S atomic sites. NEXAFS shows not only excitation into the intramolecular sigma* S–C resonance but also into a sigma* S–Au orbital perpendicular to the surface, clearly identifying the local S headgroup site as atop a Au atom. Simulations show that it is not possible, however, to distinguish between the two possible adatom reconstruction models; a single thiolate species atop a hollow-site Au adatom or a dithiolate moiety comprising two thiolate species bonded to a bridge-bonded Au adatom. Within this dithiolate moiety a second sigma* S–Au orbital that lies near parallel to the surface has a higher energy that overlaps that of the sigma* S–C resonance. The new NIXSW data show the S–C bond to be tilted by 61° relative to the surface normal, with a preferred azimuthal orientation in , corresponding to the intermolecular nearest-neighbor directions. This azimuthal orientation is consistent with the thiolate being atop a hollow-site Au adatom, but not consistent with the originally proposed Au-adatom-dithiolate moiety. However, internal conformational changes within this species could, perhaps, render this model also consistent with the experimental data
A method for atomistic spin dynamics simulations: implementation and examples
We present a method for performing atomistic spin dynamic simulations. A
comprehensive summary of all pertinent details for performing the simulations
such as equations of motions, models for including temperature, methods of
extracting data and numerical schemes for performing the simulations is given.
The method can be applied in a first principles mode, where all interatomic
exchange is calculated self-consistently, or it can be applied with frozen
parameters estimated from experiments or calculated for a fixed
spin-configuration. Areas of potential applications to different magnetic
questions are also discussed. The method is finally applied to one situation
where the macrospin model breaks down; magnetic switching in ultra strong
fields.Comment: 14 pages, 19 figure
Simulation of a spin-wave instability from atomistic spin dynamics
We study the spin dynamics of a Heisenberg model at finite temperature in the
presence of an external field or a uniaxial anisotropy. For the case of the
uniaxial anisotropy our simulations show that the macro moment picture breaks
down. An effect which we refer to as a spin-wave instability (SWI) results in a
non-dissipative Bloch-Bloembergen type relaxation of the macro moment where the
size of the macro moment changes, and can even be made to disappear. This
relaxation mechanism is studied in detail by means of atomistic spin dynamics
simulations.Comment: 8 pages, 12 figures, submitted to PR
Three-dimensional magnetic flux-closure patterns in mesoscopic Fe islands
We have investigated three-dimensional magnetization structures in numerous
mesoscopic Fe/Mo(110) islands by means of x-ray magnetic circular dichroism
combined with photoemission electron microscopy (XMCD-PEEM). The particles are
epitaxial islands with an elongated hexagonal shape with length of up to 2.5
micrometer and thickness of up to 250 nm. The XMCD-PEEM studies reveal
asymmetric magnetization distributions at the surface of these particles.
Micromagnetic simulations are in excellent agreement with the observed magnetic
structures and provide information on the internal structure of the
magnetization which is not accessible in the experiment. It is shown that the
magnetization is influenced mostly by the particle size and thickness rather
than by the details of its shape. Hence, these hexagonal samples can be
regarded as model systems for the study of the magnetization in thick,
mesoscopic ferromagnets.Comment: 12 pages, 11 figure
Magnetic versus crystal field linear dichroism in NiO thin films
We have detected strong dichroism in the Ni x-ray absorption
spectra of monolayer NiO films. The dichroic signal appears to be very similar
to the magnetic linear dichroism observed for thicker antiferromagnetic NiO
films. A detailed experimental and theoretical analysis reveals, however, that
the dichroism is caused by crystal field effects in the monolayer films, which
is a non trivial effect because the high spin Ni ground state is not
split by low symmetry crystal fields. We present a practical experimental
method for identifying the independent magnetic and crystal field contributions
to the linear dichroic signal in spectra of NiO films with arbitrary
thicknesses and lattice strains. Our findings are also directly relevant for
high spin and systems such as LaFeO, FeO,
VO, LaCrO, CrO, and Mn manganate thin films
The situation of former adolescent self-injurers as young adults: a follow-up study
Background: Nonsuicidal self-injury (NSSI) in adolescence has been described as comorbid condition in affective or anxiety disorders, as well as borderline personality disorder (BPD) and is a risk factor for later suicide attempts. Prevalence rates of NSSI decline steeply from adolescence to young adulthood. Yet, to the best of our knowledge, the longitudinal development of adolescent psychiatric patients with NSSI into their young adulthood has not been investigated. The aim of this study was to assess current NSSI and psychological impairment of young adults, who had been in treatment for NSSI in their adolescence. Methods: Former patients of the departments of child and adolescent psychiatry and psychotherapy in Ulm and Ravensburg, Germany (N = 52), who presented with NSSI in their adolescence, were recruited (average age: 21.5 years (SD = 2.6)). Data was assessed using questionnaires and structured clinical interviews. Two groups of participants with prevailing NSSI and ceased NSSI were compared concerning their current psychological impairment, history of NSSI, suicide attempts, and BPD diagnosis. Results: Around half of all participants had engaged in NSSI within the last year, and around half met diagnostic criteria for BPD. Although there was no significant association between current NSSI and BPD, an earlier age of onset of NSSI and a longer duration of NSSI during adolescence was significantly predictive of adult BPD. Two thirds of participants still met criteria of an axis 1 psychiatric disorder. Suicide attempts were reported by 53.8 % of all participants. Participants with current NSSI were more likely to meet criteria for a current axis 1 disorder, had engaged in NSSI more often in their lifetime, and reported more suicide attempts. Conclusions: Reduction of NSSI from adolescence to young adulthood was lower than described in previous community samples. This may be due to the initial high psychiatric impairment of this sample in adolescence. Early onset of NSSI seemed to be a risk factor for a longer duration of NSSI during adolescence but not for NSSI prevailing into adulthood. However, it was a risk factor for adult BPD. Furthermore, the occurrence of suicidal thoughts and behaviors and prevailing NSSI was highly associated
- …