20 research outputs found
Magnetic ordering, electronic structure and magnetic anisotropy energy in the high-spin Mn single molecule magnet
We report the electronic structure and magnetic ordering of the single
molecule magnet [MnO(2,2'-biphenoxide)Br]
based on first-principles all-electron density-functional calculations. We find
that two of the ten core Mn atoms are coupled antiferromagnetically to the
remaining eight, resulting in a ferrimagnetic ground state with total spin
S=13. The calculated magnetic anisotropy barrier is found to be 9 K in good
agreement with experiment. The presence of the Br anions impact the electronic
structure and therefore the magnetic properties of the 10 Mn atoms. However,
the electric field due to the negative charges has no significant effect on the
magnetic anisotropy.Comment: 4 pages, submitted to PR
Magnetic Field Induced Spin Polarization of AlAs Two-dimensional Electrons
Two-dimensional (2D) electrons in an in-plane magnetic field become fully
spin polarized above a field B_P, which we can determine from the in-plane
magnetoresistance. We perform such measurements in modulation-doped AlAs
electron systems, and find that the field B_P increases approximately linearly
with 2D electron density. These results imply that the product |g*|m*, where g*
is the effective g-factor and m* the effective mass, is a constant essentially
independent of density. While the deduced |g*|m* is enhanced relative to its
band value by a factor of ~ 4, we see no indication of its divergence as 2D
density approaches zero. These observations are at odds with results obtained
in Si-MOSFETs, but qualitatively confirm spin polarization studies of 2D GaAs
carriers.Comment: 4 pages, 5 figure
Quantum-classical transition of the escape rate of uniaxial antiferromagnetic particles in an arbitrarily directed field
Quantum-classical escape rate transition has been studied for uniaxial
antiferromagnetic particles with an arbitrarily directed magnetic field. In the
case that the transverse and longitudinal fileds coexist, we calculate the
phase boundary line between first- and second-order transitions, from which
phase diagrams can be obtained. It is shown that the effects of the applied
longitudinal magnetic field on quantum-classical transition vary greatly for
different relative magnitudes of the non-compensation.Comment: to be appeared in Phys. Rev.
Tunneling with dissipation and decoherence for a large spin
We present rigorous solution of problems of tunneling with dissipation and
decoherence for a spin of an atom or a molecule in an isotropic solid matrix.
Our approach is based upon switching to a rotating coordinate system coupled to
the local crystal field. We show that the spin of a molecule can be used in a
qubit only if the molecule is strongly coupled with its atomic environment.
This condition is a consequence of the conservation of the total angular
momentum (spin + matrix), that has been largely ignored in previous studies of
spin tunneling.Comment: 4 page
Semiconductive and Photoconductive Properties of the Single Molecule Magnets Mn-Acetate and FeBr
Resistivity measurements are reported for single crystals of
Mn-Acetate and FeBr. Both materials exhibit a
semiconductor-like, thermally activated behavior over the 200-300 K range. The
activation energy, , obtained for Mn-Acetate was 0.37 0.05
eV, which is to be contrasted with the value of 0.55 eV deduced from the
earlier reported absorption edge measurements and the range of 0.3-1 eV from
intramolecular density of states calculations, assuming = , the
optical band gap. For FeBr, was measured as 0.73 0.1 eV,
and is discussed in light of the available approximate band structure
calculations. Some plausible pathways are indicated based on the crystal
structures of both lattices. For Mn-Acetate, we also measured
photoconductivity in the visible range; the conductivity increased by a factor
of about eight on increasing the photon energy from 632.8 nm (red) to 488 nm
(blue). X-ray irradiation increased the resistivity, but was insensitive
to exposure.Comment: 7 pages, 8 figure
Nonequilibrium dynamics and superfluid ring excitations in binary Bose-Einstein condensates
We revisit a classic study of interpenetrating Bose-Einstein condensates in the hyperfine states |F=1,mf=-1 |1 and |F=2,mf=+1 |2 of Rb87 and observe striking new nonequilibrium component separation dynamics in the form of oscillating ringlike structures. The process of component separation is not significantly damped, a finding that also contrasts sharply with earlier experimental work, allowing a clean first look at a collective excitation of a binary superfluid. We further demonstrate extraordinary quantitative agreement between theoretical and experimental results using a multicomponent mean-field model with key additional features: the inclusion of atomic losses and the careful characterization of trap potentials (at the level of a fraction of a percent). © 2007 The American Physical Society