1,070 research outputs found
Pump-Probe Experiments on the Single-Molecule Magnet Fe8 : Measurement of Excited Level Lifetimes
We present magnetization measurements on the single molecule magnet Fe8 in
the presence of pulsed microwave radiation. A pump-probe technique is used with
two microwave pulses with frequencies of 107 GHz and 118 GHz and pulse lengths
of several nanoseconds to study the spin dynamics via time-resolved
magnetization measurements using a Hall probe magnetometer. We find evidence
for short spin-phonon relaxation times of the order of one microsecond. The
temperature dependence of the spin-phonon relaxation time in our experiments is
in good agreement with previously published theoretical results. We also
established the presence of very short energy diffusion times, that act on a
timescale of about 70 ns.Comment: submitted to Phys. Rev. Lett. (01 March 2007
Density of States of GaAs-AlGaAs Heterostructures Deduced from Temperature Dependend Magnetocapacitance Measurements
Abstract We have analyzed the density of states of a two dimensional electron gas in a GaAs- AlGaAs hetereostructure by measuring the magnetocapacitance in magnetic fields up to 6 Tesla at temperatures below 10 K. The experimental data are well described by a Gaussian-like density of states where the linewidth à is proportional to B
Latent-heat and non-linear vortex liquid at the vicinity of the first-order phase transition in layered high-Tc superconductors
In this work we revisit the vortex matter phase diagram in layered
superconductors solving still open questions by means of AC and DC local
magnetic measurements in the paradigmatic BiSrCaCuO
compound. We show that measuring with AC magnetic techniques is mandatory in
order to probe the bulk response of vortex matter, particularly at
high-temperatures where surface barriers for vortex entrance dominate. From the
-evolution of the enthalpy and latent-heat at the transition we
find that, contrary to previous reports, the nature of the dominant interlayer
coupling is electromagnetic in the whole temperature range. By studying the
dynamic properties of the phase located at , we reveal
the spanning in a considerable fraction of the phase diagram of a non-linear
vortex phase suggesting bulk pinning might play a role even in the liquid
vortex phase.Comment: arXiv admin note: substantial text overlap with arXiv:1212.456
Influence of antisymmetric exchange interaction on quantum tunneling of magnetization in a dimeric molecular magnet Mn6
We present magnetization measurements on the single molecule magnet Mn6,
revealing various tunnel transitions inconsistent with a giant-spin
description. We propose a dimeric model of the molecule with two coupled spins
S=6, which involves crystal-field anisotropy, symmetric Heisenberg exchange
interaction, and antisymmetric Dzyaloshinskii-Moriya exchange interaction. We
show that this simplified model of the molecule explains the experimentally
observed tunnel transitions and that the antisymmetric exchange interaction
between the spins gives rise to tunneling processes between spin states
belonging to different spin multiplets.Comment: 5 pages, 4 figure
Magnetization dynamics in the single-molecule magnet Fe8 under pulsed microwave irradiation
We present measurements on the single molecule magnet Fe8 in the presence of
pulsed microwave radiation at 118 GHz. The spin dynamics is studied via time
resolved magnetization experiments using a Hall probe magnetometer. We
investigate the relaxation behavior of magnetization after the microwave pulse.
The analysis of the experimental data is performed in terms of different
contributions to the magnetization after-pulse relaxation. We find that the
phonon bottleneck with a characteristic relaxation time of 10 to 100 ms
strongly affects the magnetization dynamics. In addition, the spatial effect of
spin diffusion is evidenced by using samples of different sizes and different
ways of the sample's irradiation with microwaves.Comment: 14 pages, 12 figure
Noise Measurement of Interacting Ferromagnetic Particles with High Resolution Hall Microprobes
We present our first experimental determination of the magnetic noise of a
superspinglass made of < 1 pico-liter frozen ferrofluid. The measurements were
performed with a local magnetic field sensor based on Hall microprobes operated
with the spinning current technique. The results obtained, though preliminary,
qualitatively agree with the theoretical predictions of Fluctuation-Dissipation
theorem (FDT) violation [1].Comment: 4pages, 2 figure
Melatonin Is Required for the Circadian Regulation of Sleep
Sleep is an evolutionarily conserved behavioral state whose regulation is poorly understood. A classical model posits that sleep is regulated by homeostatic and circadian mechanisms. Several factors have been implicated in mediating the homeostatic regulation of sleep, but molecules underlying the circadian mechanism are unknown. Here we use animals lacking melatonin due to mutation of arylalkylamine N-acetyltransferase 2 (aanat2) to show that melatonin is required for circadian regulation of sleep in zebrafish. Sleep is dramatically reduced at night in aanat2 mutants maintained in light/dark conditions, and the circadian regulation of sleep is abolished in free-running conditions. We find that melatonin promotes sleep downstream of the circadian clock as it is not required to initiate or maintain circadian rhythms. Additionally, we provide evidence that melatonin may induce sleep in part by promoting adenosine signaling, thus potentially linking circadian and homeostatic control of sleep
- …