arXiv subjects

B. Barbara

Publications and source records attributed to B. Barbara.

39 records · Page 3Linked to original sources

arXiv2000

Butterfly hysteresis loop and dissipative spin reversal in the S=1/2, V15 molecular complex

Time resolved magnetization measurements have been performed on a spin 1/2 molecular complex, so called V$_{15}$. Despite the absence of a barrier, magnetic hysteresis is observed over a timescale of several seconds. A detailed analysis in terms of a dissipative two level model is given, in which fluctuations and splittings are of same energy. Spin-phonon coupling leads to long relaxation times and to a particular "butterfly" hysteresis loop.

cond-mat.mes-hall↗

arXiv2000

Non-adiabatic Landau-Zener transitions in low spin molecular magnet V15

The V_{15} polyoxovanadate molecule is made of 15 spins 1/2 with antiferromagnetic couplings. It belongs to the class of molecules with very large Hilbert space dimension (2^{15} in V_{15}, 10^8 in Mn_{12}-ac). It is a low-spin/big-molecule with spin S=1/2. Contrary large-spins/big-molecules of the Mn_{12}-ac type, V_{15} has no energy barrier against spin rotation. Magnetization measurements have been performed and despite the absence of a barrier, magnetic hysteresis is observed over a timescale of several seconds. This new phenomenon characterized by a "butterfly" hysteresis loop is due to the effect of the environment on the quantum rotation of the entangled 15 spins of the molecule, in which the phonon density of states is not at its equilibrium (phonon bottleneck).

cond-mat.mes-hall↗

arXiv1999

Classical and quantum magnetisation reversal studied in single nanometer-sized particles and clusters using micro-SQUIDs

Recent progress in experiment on quantum tunnelling of the magnetic moment in mesoscopic systems will be reviewed. The emphasis will be made on measurements of individual nanoparticles. These nanomagnets allow one to test the border between classical and quantum behaviour. Using the micro-SQUID magnetometer, waiting time, switching field and telegraph noise measurements show unambiguously that the magnetisation reversal of small enough single crystalline nanoparticles is described by a model of thermal activation over a single-energy barrier. Results on insulating BaFeO nanoparticles show strong deviations from this model below 0.4 K which agree with the theory of macroscopic quantum tunnelling in the low dissipation regime.

cond-mat.mes-hall↗