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

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