125 research outputs found
Optical-phonon-mediated charge transport in substituted morpholinium TCNQ2 salts
Substituted morphollnium TCNQ2 compounds exhibit some universal features with respect to the field, frequency and temperature dependence of the conductivity. These characteristics are different from the closely related morphollnlum TCNQI compounds. We show that a natural way to account for these phenomena comes about by careful examination of the order parameter space, i.e. the space created by the two different order parameters which together determine the gap at the Fermi surface: (i) the regular Pelerls dimerization of the acceptor-acceptor overlap and (li) a coherent shift of the donor ~olecules with respect to the accep$ors. By describing small revolutions through parameter space (realized by phase coupling of two different phonons producing the above mentioned gap) the ground state electron gas is shifted with respect to the lattice, thereby producing a current. The model allows for a qualitative description of conductivityrelated phenomena in these systems
Superparamagnetic behaviour of antiferromagnetic DyPO4 nanoparticles
We report on the low-temperature magnetic ac-susceptibility of
antiferromagnetic DyPO4 nanoparticles with a very high surface to volume ratio.
The results are interpreted in terms of superparamagnetic relaxation of the
Neel vector arising from a relatively large number approx 0.2 Na of
uncompensated spins probably existing on the surface of the nanoparticles. The
activation energy of the relaxation process is found to be Ea / kB = (2.6+-0.1)
K within a model taking into account the magnetic interaction between
nanoparticles.Comment: 3 pages, 1 figure, Espcrc2, ICM0
Phase diagrams of weakly anisotropic Heisenberg antiferromagnets: II. Quasi 2-dimensional systems
Quantum Matter and Optic
Spin-Peierls transition in a Cu2+ linear chain
Metals in Catalysis, Biomimetics & Inorganic Material
Quantum tunnelling of magnetization in Mn12-ac studied by 55Mn NMR
We present an ultra-low temperature study (down to T = 20 mK) of the nuclear
spin-lattice relaxation (SLR) in the 55Mn nuclei of the molecular magnet
Mn12-ac. The nuclear spins act as local probes for the electronic spin
fluctuations, due to thermal excitations and to tunnelling events. In the
quantum regime (below T = 0.75 K), the nuclear SLR becomes
temperature-independent and is driven by fluctuations of the cluster's
electronic spin due to the quantum tunnelling of magnetization in the ground
doublet. The quantitative analysis of the nuclear SLR shows that the presence
of fast-tunnelling molecules, combined with nuclear intercluster spin
diffusion, plays an important role in the relaxation process.Comment: RevTex, 5 pages, 3 eps figures; presented at the Internation
Conference on Molecular Magnets (Valencia, 5 - 10 Oct. 2002); to be published
in Polyhedro
High-field (40 T) magnetization studies of linear Heisenberg chains with alternating exchange
Metals in Catalysis, Biomimetics & Inorganic Material
Non-linear excitations in Ising-type magnetic chain systems I: Mossbauer relaxation studies of antiferromagnets in zero and applied field
Quantum Matter and Optic
Nuclear spin dynamics in the quantum regime of a single-molecule magnet
Quantum Matter and Optic
Field-dependent Mossbauer relaxation study of domain walls in the quasi 1-d antiferromagnet RbFeCl3.2H2O
Quantum Matter and Optic
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