1,311 research outputs found
Tunneling Splittings in Mn12-Acetate Single Crystals
A Landau-Zener multi-crossing method has been used to investigate the tunnel
splittings in high quality Mn-acetate single crystals in the pure
quantum relaxation regime and for fields applied parallel to the magnetic easy
axis. With this method several individual tunneling resonances have been
studied over a broad range of time scales. The relaxation is found to be
non-exponential and a distribution of tunnel splittings is inferred from the
data. The distributions suggest that the inhomogeneity in the tunneling rates
is due to disorder that produces a non-zero mean value of the average
transverse anisotropy, such as in a solvent disorder model. Further, the effect
of intermolecular dipolar interaction on the magnetic relaxation has been
studied.Comment: Europhysics Letters (in press). 7 pages, including 3 figure
Fabrication of Nano-Gapped Single-Electron Transistors for Transport Studies of Individual Single-Molecule Magnets
Three terminal single-electron transistor devices utilizing Al/Al2O3 gate
electrodes were developed for the study of electron transport through
individual single-molecule magnets. The devices were patterned via multiple
layers of optical and electron beam lithography. Electromigration induced
breaking of the nanowires reliably produces 1-3 nm gaps between which the SMM
can be situated. Conductance through a single Mn12(3-thiophenecarboxylate)
displays the coulomb blockade effect with several excitations within +/- 40
meV.Comment: 10 pages, 5 figure
Phonon-Induced Quantum Magnetic Deflagration in Mn12
A comprehensive set of experiments on the effect of high-frequency surface
acoustic waves, SAWs, in the spin relaxation in Mn12-acetate is presented. We
have studied the quantum magnetic deflagration induced by SAWs under various
experimental conditions extending the data shown in a very recent paper [A.
Hernandez-Minguez et. al., Phys. Rev. Lett. 95, 217205 (2005)]. We have focused
our study on the dependence of both the ignition time and the propagation speed
of the magnetic avalanches on the frequency, amplitude, and duration of the SAW
pulses in experiments performed under different temperatures and external
magnetic fields.Comment: 7 pages, 9 figure
How to distinguish between interacting and noninteracting molecules in tunnel junctions
Recent experiments demonstrate a temperature control of the electric
conduction through a ferrocene-based molecular junction. Here we examine the
results in view of determining means to distinguish between transport through
single-particle molecular levels or via transport channels split by Coulomb
repulsion. Both transport mechanisms are similar in molecular junctions given
the similarities between molecular intralevel energies and the charging energy.
We propose an experimentally testable way to identify the main transport
process. By applying a magnetic field to the molecule, we observe that an
interacting theory predicts a shift of the conductance resonances of the
molecule whereas in the noninteracting case each resonance is split into two
peaks. The interaction model works well in explaining our experimental results
obtained in a ferrocene-based single-molecule junction, where the charge
degeneracy peaks shift (but do not split) under the action of an applied
7-Tesla magnetic field. This method is useful for a proper characterization of
the transport properties of molecular tunnel junctions.Comment: Main text: 7 pages, 5 figures; SI: 2 pages, 2 figures. Accepted to
RSC Nanoscal
Observation of a Distribution of Internal Transverse Magnetic Fields in a Mn12-Based Single Molecule Magnet
A distribution of internal transverse magnetic fields has been observed in
single molecule magnet (SMM) Mn12-BrAc in the pure magnetic quantum tunneling
(MQT) regime. Magnetic relaxation experiments at 0.4 K are used to produce a
hole in the distribution of transverse fields whose angle and depth depend on
the orientation and amplitude of an applied transverse ``digging field.'' The
presence of such transverse magnetic fields can explain the main features of
resonant MQT in this material, including the tunneling rates, the form of the
relaxation and the absence of tunneling selection rules. We propose a model in
which the transverse fields originate from a distribution of tilts of the
molecular magnetic easy axes.Comment: 4 page
Low temperature microwave emission from molecular clusters
We investigate the experimental detection of the electromagnetic radiation
generated in the fast magnetization reversal in Mn12-acetate at low
temperatures. In our experiments we used large single crystals and assemblies
of several small single crystals of Mn12-acetate placed inside a cylindrical
stainless steel waveguide in which an InSb hot electron device was also placed
to detect the radiation. All this was set inside a SQUID magnetometer that
allowed to change the magnetic field and measure the magnetic moment and the
temperature of the sample as the InSb detected simultaneously the radiation
emitted from the molecular magnets. Our data show a sequential process in which
the fast inversion of the magnetic moment first occurs, then the radiation is
detected by the InSb device, and finally the temperature of the sample
increases during 15 ms to subsequently recover its original value in several
hundreds of milliseconds.Comment: changed conten
Can social robots affect children's prosocial behavior? An experimental study on prosocial robot models
The aim of this study was to investigate whether a social robot that models prosocial behavior (in terms of giving away stickers) influences the occurrence of prosocial behavior among children as well as the extent to which children behave prosocially. Additionally, we investigated whether the occurrence and extent of children's prosocial behavior changed when being repeated and whether the behavior modeled by the robot affected children's norms of prosocial behavior. In a one-factorial experiment (weakly prosocial robot vs. strongly prosocial robot), 61 children aged 8 to 10 and a social robot alternately played four rounds of a game against a computer and, after each round, could decide to give away stickers. Children who saw a strongly prosocial robot gave away more stickers than children who saw a weakly prosocial robot. A strongly prosocial robot also increased children's perception of how many other children engage in prosocial behavior (i.e., descriptive norms). The strongly prosocial robot affected the occurrence of prosocial behavior only in the first round, whereas its effect on the extent of children's prosocial behavior was most distinct in the last round. Our study suggests that the principles of social learning also apply to whether children learn prosocial behavior from robots
Immediate and late impact of reperfusion therapies in acute pulmonary embolism
Haemodynamic instability and right ventricular dysfunction are the key determinants of short-term prognosis in patients with acute pulmonary embolism (PE). Residual thrombi and persistent right ventricular dysfunction may contribute to post-PE functional impairment, and influence the risk of developing chronic thromboembolic pulmonary hypertension. Patients with haemodynamic instability at presentation (high-risk PE) require immediate primary reperfusion to relieve the obstruction in the pulmonary circulation and increase the chances of survival. Surgical removal of the thrombi or catheter-directed reperfusion strategies is alternatives in patients with contraindications to systemic thrombolysis. For haemodynamically stable patients with signs of right ventricular overload or dysfunction (intermediate-risk PE), systemic standard-dose thrombolysis is currently not recommended, because the risk of major bleeding associated with the treatment outweighs its benefits. In such cases, thrombolysis should be considered only as a rescue intervention if haemodynamic decompensation develops. Catheter-directed pharmaco-logical and pharmaco-mechanical techniques ensure swift recovery of echocardiographic and haemodynamic parameters and may be characterized by better safety profile than systemic thrombolysis. For survivors of acute PE, little is known on the effects of reperfusion therapies on the risk of chronic functional and haemodynamic impairment. In intermediate-risk PE patients, available data suggest that systemic thrombolysis may have little impact on long-term symptoms and functional limitation, echocardiographic parameters, and occurrence of chronic thromboembolic pulmonary hypertension. Ongoing and future interventional studies will clarify whether 'safer' reperfusion strategies may improve early clinical outcomes without increasing the risk of bleeding and contribute to reducing the burden of long-term complications after intermediate-risk PE
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