1,796 research outputs found
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
Determination of the magnetic anisotropy axes of single-molecule magnets
Simple methods are presented allowing the determination of the magnetic
anisotropy axes of a crystal of a single-molecule magnet (SMM). These methods
are used to determine an upper bound of the easy axis tilts in a standard
Mn12-Ac crystal. The values obtained in the present study are significately
smaller than those reported in recent high frequency electron paramagnetic
resonance (HF-EPR) studies which suggest distributions of hard-axes tilts.Comment: 10 pages, 6 figure
Resonant Tunneling in Truly Axial Symmetry Mn12 Single-Molecule Magnets: Sharp Crossover between Thermally Assisted and Pure Quantum Tunneling
Magnetization measurements of a truly axial symmetry Mn12-tBuAc molecular
nanomagnet with a spin ground state of S = 10 show resonance tunneling. This
compound has the same magnetic anisotropy as Mn12-Ac but the molecules are
better isolated and the crystals have less disorder and a higher symmetry.
Hysteresis loop measurements at several temperatures reveal a well-resolved
step fine-structure which is due to level crossings of excited states. All step
positions can be modeled by a simple spin Hamiltonian. The crossover between
thermally assisted and pure quantum tunneling can be investigated with
unprecedented detail.Comment: 5 pages, 6 figure
Construction of Simulation Wavefunctions for Aqueous Species: D3O+
This paper investigates Monte Carlo techniques for construction of compact
wavefunctions for the internal atomic motion of the D3O+ ion. The polarization
force field models of Stillinger, et al and of Ojamae, et al. were used.
Initial pair product wavefunctions were obtained from the asymptotic high
temperature many-body density matrix after contraction to atom pairs using
Metropolis Monte Carlo. Subsequent characterization shows these pair product
wavefunctions to be well optimized for atom pair correlations despite that fact
that the predicted zero point energies are too high. The pair product
wavefunctions are suitable to use within variational Monte Carlo, including
excited states, and density matrix Monte Carlo calculations. Together with the
pair product wavefunctions, the traditional variational theorem permits
identification of wavefunction features with significant potential for further
optimization. The most important explicit correlation variable found for the
D3O+ ion was the vector triple product {\bf r}({\bf
r}{\bf r}). Variational Monte Carlo with 9 of such
explicitly correlated functions yielded a ground state wavefunction with an
error of 5-6% in the zero point energy.Comment: 17 pages including 6 figures, typos correcte
'Diverse mobilities': second-generation Greek-Germans engage with the homeland as children and as adults
This paper is about the children of Greek labour migrants in Germany. We focus on two life-stages of ‘return’ for this second generation: as young children brought to Greece on holidays or sent back for longer periods, and as young adults exercising an independent ‘return’ migration. We draw both on literature and on our own field interviews with 50 first- and second-generation Greek-Germans. We find the practise of sending young children back to Greece to have been surprisingly widespread yet little documented. Adult relocation to the parental homeland takes place for five reasons: (i) a ‘search for self’; (ii) attraction of the Greek way of life; (iii) the actualisation of the ‘family narrative of return’ by the second, rather than the first, generation; (iv) life-stage events such as going to university or marrying a Greek; (v) escape from a traumatic event or oppressive family situation. Yet the return often brings difficulties, disillusionment, identity reappraisal, and a re-evaluation of the German context
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