392 research outputs found
Determinants of short-period heart rate variability in the general population
Decreased heart rate variability (HRV) is associated with a worse prognosis in a variety of diseases and disorders. We evaluated the determinants of short-period HRV in a random sample of 149 middle-aged men and 137 women from the general population. Spectral analysis was used to compute low-frequency (LF), high-frequency (HF) and total-frequency power. HRV showed a strong inverse association with age and heart rate in both sexes with a more pronounced effect of heart rate on HRV in women. Age and heart rate-adjusted LF was significantly higher in men and HF higher in women. Significant negative correlations of BMI, triglycerides, insulin and positive correlations of HDL cholesterol with LF and total power occurred only in men. In multivariate analyses, heart rate and age persisted as prominent independent predictors of HRV. In addition, BMI was strongly negatively associated with LF in men but not in women, We conclude that the more pronounced vagal influence in cardiac regulation in middle-aged women and the gender-different influence of heart rate and metabolic factors on HRV may help to explain the lower susceptibility of women for cardiac arrhythmias. Copyright (C) 2001 S. Karger AG, Basel
Influence of exchange bias coupling on the single-crystalline FeMn ultrathin film
Polarization dependent x-ray photoemission electron microscopy was used to investigate the influence of the exchange bias coupling on the disordered ultrathin single-crystalline fcc Fe50 Mn50. We find that the critical thickness of the FeMn film, where the antiferromagnetic (AF) order is formed, varies with changing the magnetization direction of the ferromagnetic (FM) layer from out-of-plane to in-plane. Surface magneto-optical Kerr effect measurements (SMOKE) further manifest the shift of the critical thickness with alternating the exchange bias coupling. It indicates that the spin structure of the FeMn layer near the FM layer is modified by the presence of exchange bias coupling and the properties of the coupling. Our results provide direct experimental evidence that the AF spin structure at the interface between the FM and AF layers is strongly influenced by the exchange bias coupling. © 2005 American Institute of Physics.published_or_final_versio
Influence of topography and Co domain walls on the magnetization reversal of the FeNi layer in FeNi/AlO/Co magnetic tunnel junctions
We have studied the magnetization reversal dynamics of FeNi/AlO/Co
magnetic tunnel junctions deposited on step-bunched Si substrates using
magneto-optical Kerr effect and time-resolved x-ray photoelectron emission
microscopy combined with x-ray magnetic circular dichroism (XMCD-PEEM).
Different reversal mechanisms have been found depending on the substrate miscut
angle. Larger terraces (smaller miscut angles) lead to a higher nucleation
density and stronger domain wall pinning. The width of domain walls with
respect to the size of the terraces seems to play an important role in the
reversal. We used the element selectivity of XMCD-PEEM to reveal the strong
influence of the stray field of domain walls in the hard magnetic layer on the
magnetic switching of the soft magnetic layer.Comment: 8 Pages, 7 Figure
Dynamics of magnetic domain wall motion after nucleation: Dependence on the wall energy
The dynamics of magnetic domain wall motion in the FeNi layer of a
FeNi/Al2O3/Co trilayer has been investigated by a combination of x-ray magnetic
circular dichroism, photoelectron emission microscopy, and a stroboscopic
pump-probe technique. The nucleation of domains and subsequent expansion by
domain wall motion in the FeNi layer during nanosecond-long magnetic field
pulses was observed in the viscous regime up to the Walker limit field. We
attribute an observed delay of domain expansion to the influence of the domain
wall energy that acts against the domain expansion and that plays an important
role when domains are small.Comment: Accepted for publication in Physical Review Letter
Ferromagnetic coupling of mononuclear Fe centers in a self-assembled metal-organic network on Au(111)
The magnetic state and magnetic coupling of individual atoms in nanoscale
structures relies on a delicate balance between different interactions with the
atomic-scale surrounding. Using scanning tunneling microscopy, we resolve the
self-assembled formation of highly ordered bilayer structures of Fe atoms and
organic linker molecules (T4PT) when deposited on a Au(111) surface. The Fe
atoms are encaged in a three-dimensional coordination motif by three T4PT
molecules in the surface plane and an additional T4PT unit on top. Within this
crystal field, the Fe atoms retain a magnetic ground state with easy-axis
anisotropy, as evidenced by X-ray absorption spectroscopy and X-ray magnetic
circular dichroism. The magnetization curves reveal the existence of
ferromagnetic coupling between the Fe centers
Temperature-induced sign change of the magnetic interlayer coupling in Ni/Ni25Mn75/Ni trilayers on Cu3Au(001)
We investigated the magnetic interlayer coupling between two ferromagnetic
(FM) Ni layers through an antiferromagnetic (AFM) Ni 25Mn75 layer and the
influence of this coupling on the exchange bias phenomenon. The interlayer
coupling energy of an epitaxial trilayer of 14 atomic monolayers (ML) Ni/45 ML
Ni 25Mn75/16 ML Ni on Cu3Au(001) was extracted from minor-loop magnetization
measurements using in-situ magneto-optical Kerr effect. The interlayer
coupling changes from ferromagnetic to antiferromagnetic when the temperature
is increased above 300 K. This sign change is interpreted as the result of the
competition between an antiparallel Ruderman-Kittel-Kasuya-Yosida (RKKY)-type
interlayer coupling, which dominates at high temperature, and a stronger
direct exchange coupling across the AFM layer, which is present only below the
NĂ©el temperature of the AFM layer
Interplay between magnetic anisotropy and interlayer coupling in nanosecond magnetization reversal of spin-valve trilayers
The influence of magnetic anisotropy on nanosecond magnetization reversal in
coupled FeNi/Cu/Co trilayers was studied using a photoelectron emission
microscope combined with x-ray magnetic circular dicroism. In quasi-isotropic
samples the reversal of the soft FeNi layer is determined by domain wall
pinning that leads to the formation of small and irregular domains. In samples
with uniaxial magnetic anisotropy, the domains are larger and the influence of
local interlayer coupling dominates the domain structure and the reversal of
the FeNi layer
Magnetostatic coupling of 90° domain walls in Fe19Ni81/Cu/Co trilayers
The magnetic interlayer coupling of Fe19Ni81/Cu/Co trilayered microstructures
has been studied by means of x-ray magnetic circular dichroism in combination
with photoelectron emission microscopy (XMCD-PEEM). We find that a parallel
coupling between magnetic domains coexists with a non-parallel coupling
between magnetic domain walls (DWs) of each ferromagnetic layer. We attribute
the non-parallel coupling of the two magnetic layers to local magnetic stray
fields arising at DWs in the magnetically harder Co layer. In the magnetically
softer FeNi layer, non-ordinary DWs, such as 270° and 90° DWs with overshoot
of the magnetization either inwards or outwards relative to the turning
direction of the Co magnetization, are identified. Micromagnetic simulations
reveal that in the absence of magnetic anisotropy, both types of overshooting
DWs are energetically equivalent. However, if a uniaxial in-plane anisotropy
is present, the relative orientation of the DWs with respect to the anisotropy
axis determines which of these DWs is energetically favorable
Magnetic coupling of porphyrin molecules through graphene
Graphene is expected to complement todays Si-based information technology. In
particular, magnetic molecules in contact with graphene constitute a
tantalizing approach towards organic spin electronics because of the reduced
conductivity mismatch at the interface. In such a system a bit is represented
by a single molecular magnetic moment, which must be stabilized against thermal
fluctuations. Here, we show in a combined experimental and theoretical study
that the moments of paramagnetic Co-octaethylporphyrin (CoOEP) molecules on
graphene can be aligned by a remarkable antiferromagnetic coupling to a Ni
substrate underneath the graphene. This coupling is mediated via the \pi\
electronic system of graphene, while no covalent bonds between the molecule and
the substrate are established.Comment: 27 pages, 12 figures, Accepted at Adv. Mate
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