Amalia Coldea

Abstract:

Magnetotransport measurements have been performed on single crystals Of kappa-(BEDT-TTF)(2)Cu(NCS)(2) in fields of up to 33 T at temperatures between 500 mK and 4.2K. Using a diamond anvil cell mounted on a goniometer, measurements of the angle and temperature dependence of the interlayer resistance, R-zz, under hydrostatic pressures between 1.1 kbar and 17.3 kbar were performed. For the first time we have been able to measure angle-dependent magnetoresistance oscillations under pressure due to both the 1D and 2D Fermi surfaces in addition to Shubnikov de Haas oscillations. The results show that the shape of the elliptical quasi-2D Fermi-pocket is more elongated under a hydrostatic pressure of 9.8 kbar compared with ambient pressure. When the magnetic field B is close to parallel to the highly conductive plane, bc, a peak in R-zz is observed with an angular width determined by the ratio of the maximum inter- and intra-layer Fermi velocities. The width of this peak is found to increase with pressure suggesting that the Fermi surface becomes more three-dimensional upon application of pressure.

Abstract:

We report millimeter-wave magneto-optical measurements on the high-spin molecule, Cr10 (OMe) 20 (O2 CCMe3) 10. The dependence of the electron paramagnetic resonance as a function of orientation and temperature demonstrates that this compound behaves as a single molecule magnet, and exhibits one of the smallest zero-field splittings (D=-0.045±0.004 K) yet reported for such a system. © 2005 American Institute of Physics.

Abstract:

We report high-field magnetotransport measurements on β″-(BEDT- TTF)4[(H3O)M(C2O4) 3]· solvent, where M=Ga³⁺, Cr³⁺ and Fe³⁺ and solvent=C5H5N. In spite of their differing transition metal-ions, M, the three compounds exhibit similar magnetic quantum oscillation spectra superimposed on a positive magnetoresistance. At least four independent quantum oscillation frequencies have been identified, corresponding to two different hole and electron pockets of the Fermi surface which follow the rules of a compensated metal. Observation of the small pockets could be the result of the Fermi surface reconstruction induced by a possible density wave. The effective masses are very similar for different samples and for different pockets range between meff ≈ 0.5-1.1 me whereas the Dingle temperatures varies between TD ≈ 1.4-4 K. At low temperature, the longitudinal magnetoresistance violates Kohler's rule, suggesting that the interlayer transport in these quasi-2D systems cannot be related to a single scattering time and that the disorder plays an important role. © EDP Sciences.