7,995 research outputs found
Answer to the comment of Chudnovsky: On the square-root time relaxation in molecular nanomagnets
Answer to the comment of E. Chudnovsky concerning the following papers:
(1) N.V. Prokof'ev, P.C.E. Stamp, Phys. Rev. Lett.80, 5794 (1998).
(2) W. Wernsdorfer, T. Ohm, C. Sangregorio, R. Sessoli, D. Mailly, C.
Paulsen, Phys. Rev. Lett. 82, 3903 (1999).Comment: 1 page
Classical and quantum magnetisation reversal studied in single nanometer-sized particles and clusters using micro-SQUIDs
Recent progress in experiment on quantum tunnelling of the magnetic moment in
mesoscopic systems will be reviewed. The emphasis will be made on measurements
of individual nanoparticles. These nanomagnets allow one to test the border
between classical and quantum behaviour. Using the micro-SQUID magnetometer,
waiting time, switching field and telegraph noise measurements show
unambiguously that the magnetisation reversal of small enough single
crystalline nanoparticles is described by a model of thermal activation over a
single-energy barrier. Results on insulating BaFeO nanoparticles show strong
deviations from this model below 0.4 K which agree with the theory of
macroscopic quantum tunnelling in the low dissipation regime.Comment: 6 pages, 2 figures, conference proceedings of LT22-Helsink
Influence of the Dzyaloshinskii-Moriya exchange interaction on quantum phase interference of spins
Magnetization measurements of a Mn12mda wheel single-molecule magnet with a
spin ground state of S = 7 show resonant tunneling and quantum phase
interference, which are established by studying the tunnel rates as a function
of a transverse field applied along the hard magnetization axis.
Dzyaloshinskii-Moriya (DM) exchange interaction allows the tunneling between
different spin multiplets. It is shown that the quantum phase interference of
these transitions is strongly dependent on the direction of the DM vector.Comment: 5 pages, 5 figure
Quantum nucleation in a single-chain magnet
The field sweep rate (v=dH/dt) and temperature (T) dependence of the
magnetization reversal of a single-chain magnet (SCM) is studied at low
temperatures. As expected for a thermally activated process, the nucleation
field (H_n) increases with decreasing T and increasing v. The set of H_n(T,v)
data is analyzed with a model of thermally activated nucleation of
magnetization reversal. Below 1 K, H_n becomes temperature independent but
remains strongly sweep rate dependent. In this temperature range, the reversal
of the magnetization is induced by a quantum nucleation of a domain wall that
then propagates due to the applied field.Comment: 5 pages, 4 figure
Resonant photon absorption in the low spin molecule V15
We report the first study of the micro-SQUID response of a molecular system
to electromagnetic radiation. The advantages of our micro-SQUID technique in
respect to pulsed electron paramagnetic resonance (EPR) techniques consist in
the possibility to perform time-resolved experiments (below 1 ns) on
submicrometer sizes samples (about 1000 spins) at low temperature (below 100
mK).
Resonant photon absorption in the GHz range was observed via low temperature
micro-SQUID magnetization measurements of the spin ground state S = 1/2 of the
molecular complex V15. The line-width essentially results from intra-molecular
hyperfine interaction. The results point out that observing Rabi oscillations
in molecular nanomagnets requires well isolated low spin systems and high
radiation power. Our first results open the way for time-resolved observations
of quantum superposition of spin-up and spin-down states in SMMs.Comment: 7 pages, 5 figure
Nonadiabatic Landau Zener tunneling in Fe_8 molecular nanomagnets
The Landau Zener method allows to measure very small tunnel splittings \Delta
in molecular clusters Fe_8. The observed oscillations of \Delta as a function
of the magnetic field applied along the hard anisotropy axis are explained in
terms of topological quantum interference of two tunnel paths of opposite
windings. Studies of the temperature dependence of the Landau Zener transition
rate P gives access to the topological quantum interference between exited spin
levels. The influence of nuclear spins is demonstrated by comparing P of the
standard Fe_8 sample with two isotopically substituted samples. The need of a
generalized Landau Zener transition rate theory is shown.Comment: 5 pages, 6 figure
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