1,715 research outputs found
Magnetization Process of Nanoscale Iron Cluster
Low-temperature magnetization process of the nanoscale iron cluster in
linearly sweeped fields is investigated by a numerical analysis of
time-dependent Schrdinger equation and the quantum master
equation. We introduce an effective basis method extracting important states,
by which we can obtain the magnetization process effectively. We investigate
the structure of the field derivative of the magnetization. We find out that
the antisymmetric interaction determined from the lattice structure reproduces
well the experimental results of the iron magnets and that this interaction
plays an important role in the iron cluster. Deviations from the adiabatic
process are also studied. In the fast sweeping case, our calculations indicate
that the nonadiabatic transition dominantly occurs at the level crossing for
the lowest field. In slow sweeping case, due to the influence of the thermal
environment to the spin system, the field derivative of the magnetization shows
an asymmetric behavior, the magnetic Fhn effect, which explains
the substructure of the experimental results in the pulsed field.Comment: 5 pages of text and 2 pages of 6 figures. To appear in J. Phys. Soc.
Jp
Sequential Tunneling through Molecular Spin Rings
We consider electrical transport through molecules with Heisenberg-coupled
spins arranged in a ring structure in the presence of an easy-axis anisotropy.
The molecules are coupled to two metallic leads and a gate. In the charged
state of the ring, a Zener double-exchange mechanism links transport properties
to the underlying spin structure. This leads to a remarkable contact-site
dependence of the current, which for an antiferromagnetic coupling of the spins
can lead to a total suppression of the zero-bias conductance when the molecule
is contacted at adjacent sites.Comment: 4 pages, 3 figure
Impact of Z_2 monopoles and vortices on the deconfinement transition
The impact of Z_2-monopoles and vortices on the bulk and the deconfinement
phase transitions of the SU(2) lattice gauge theory with a mixed Villain form
of action is investigated by varying their numbers with appropriate chemical
potentials. Suppressing the former shifts the line of deconfinement transitions
in the coupling plane but it continues to behave also like the bulk transition
line. We find separate deconfinement and bulk phase transitions on the same
lattice, suggesting the two to be indeed coincident at higher adjoint
couplings. Universality is restored when both monopoles and vortices are
suppressed.Comment: LATTICE99(Finite Temp I), 3 pages, 3 eps figures, LaTeX, espcrc2.st
Nuclear spin relaxation in ordered bimetallic chain compounds
A theoretical interpretation is given to recent proton spin relaxation-time
(T_1) measurements on NiCu(C_7H_6N_2O_6)(H_2O)_32H_2O, which is an ideal
one-dimensional ferrimagnetic Heisenberg model system of alternating spins 1
and 1/2. The relaxation rate T_1^{-1} is formulated in temrs of the spin-wave
theory and is evaluated by the use of a quantum Monte Carlo method.
Calculations of the temperature and applied-field (H) dependences of T_1^{-1}
are in total agreement with the experimental findings. T_1 behaves as
, which turns out an indirect observation of the
quadratic dispersion relations dominating the low-energy physics of quantum
ferrimagnets.Comment: 5 pages, 4 figures embedded, to appear in Phys. Lett.
Landau Zener method to study quantum phase interference of Fe8 molecular nanomagnets
We present details about an experimental method based on the Landau Zener
model which allows to measure very small tunnel splittings in
molecular clusters Fe8. The measurements are performed with an array of
micro-SQUIDs. 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.
Transitions between M = -S and (S - n), with n even or odd, revealed a parity
(symmetry) effect which is analogous to the suppression of tunneling predicted
for half integer spins. This observation is the first direct evidence of the
topological part of the quantum spin phase (Berry phase) in a magnetic system.
The influence of intermolecular dipole interactions on the measured tunnel
splittings are shown.Comment: 6 pages, 14 figures, conference proceedings of MMM 1999, San Jose,
15-18 Nov., session number CD-0
Phonon-assisted tunneling in the quantum regime of Mn12-ac
Longitudinal or transverse magnetic fields applied on a crystal of Mn12-ac
allows to observe independent tunnel transitions between m=-S+p and m=S-n-p
(n=6-10, p=0-2 in longitudinal field and n=p=0 in transverse field). We observe
a smooth transition (in longitudinal) from coherent ground-state to thermally
activated tunneling. Furthermore two ground-state relaxation regimes showing a
crossover between quantum spin relaxation far from equilibrium and near
equilibrium, when the environment destroys multimolecule correlations. Finally,
we stress that the complete Hamiltonian of Mn12 should contain odd spin
operators of low order
Remote File Access: A Data-Access Protocol for Computer Networks
This paper deals with defining and implementing high-level protocols for computer networks, a subject now being studied by private, national, and international organizations. While line-level protocols already exist in standard formats, and these organizations are defining end-to-end protocols, higher level protocols are still a matter for study. Since some services have to be provided by a computer network, such services must use standardized protocols if portability, compatibility, and internetworking are to be achieved. This paper considers a possible network service and its related protocol
Glauber slow dynamics of the magnetization in a molecular Ising chain
The slow dynamics (10^-6 s - 10^4 s) of the magnetization in the paramagnetic
phase, predicted by Glauber for 1d Ising ferromagnets, has been observed with
ac susceptibility and SQUID magnetometry measurements in a molecular chain
comprising alternating Co{2+} spins and organic radical spins strongly
antiferromagnetically coupled. An Arrhenius behavior with activation energy
Delta=152 K has been observed for ten decades of relaxation time and found to
be consistent with the Glauber model. We have extended this model to take into
account the ferrimagnetic nature of the chain as well as its helicoidal
structure.Comment: 4 pages, 4 figures (low resolution), 16 references. Submitted to
Physical Review Letter
Patterning molecular scale paramagnets at Au Surface: A root to Magneto-Molecular-Electronics
Few examples of the exploitation of molecular magnetic properties in
molecular electronics are known to date. Here we propose the realization of
Self assembled monolayers (SAM) of a particular stable organic radical. This
radical is meant to be used as a standard molecule on which to prove the
validity of a single spin reading procedure known as ESR-STM. We also discuss a
range of possible applications, further than ESR-STM, of magnetic monolayers of
simple purely organic magnetic molecule.Comment: This preprint is currently partially under revisio
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