Quantum matter in high magnetic fields

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Electron paramagnetic resonance studies of the high-spin molecule Cr10(OMe)20(O2CCMe3)10 -: art. no. 03250

APPLIED PHYSICS LETTERS 86:3 (2005) ARTN 032507

Authors:

S Sharmin, A Ardavan, SJ Blundell, AI Coldea, EJL McInnes, D Low
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Fermiology of new charge-transfer salts, β″-(BEDT-TTF) 4[(H3O)M(C2O4)3]-solvent where M = Ga, Cr and Fe

Journal De Physique IV JP 114 (2004) 205-209

Authors:

AI Coldea, AF Bangura, A Ardavan, J Singleton, A Akutsu-Sato, H Akutsu, SS Turner, P Day

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.
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The effect of magnetic ions and disorder on superconducting β″-(BEDT-TTF)4[(H3O)M(C2O 4)3]· C6H5NO2 salts, where M = Ga and Cr

Journal De Physique IV JP 114 (2004) 285-287

Authors:

AF Bangura, AI Coldea, A Ardavan, J Singleton, A Akutsu-Sato, H Akutsu, P Day

Abstract:

We report magnetotransport measurements performed in magnetic fields of up to 33 T and at low temperatures (0.45 K4[(H3O)M(C2O4)3]· C6H5NO2, where the 3d metal ion M is either non-magnetic Ga3+ or magnetic Cr3+, Quantum oscillations suggest that the salt with M = Ga has two two-dimensional Fermi surface pockets (45 T and 230 T) whereas when M = Cr only one pocket (230 T) is observed. Replacing Ga with Cr has the effect of enhancing the effective mass of the 230 T pocket from 1.2 ± 0.2 me to 2.2 ± 0,3 me and reducing the superconducting critical temperature from Tc ≈ 8 K to Tc ≈ 5 K. © EDP Sciences.
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The role of magnetic ions on the magnetotransport properties of the charge-transfer salts β″-BEDT-[()()] where =, Cr3+ or Fe3+

Journal of Magnetism and Magnetic Materials Elsevier BV 272-276 (2004) 1062-1064

Authors:

AI Coldea, AF Bangura, J Singleton, A Ardavan, A Akutsu-Sato, H Akutsu, S S. Turner, P Day
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The role of magnetic ions on the magnetotransport properties of the charge-transfer salts beta ''-BEDT-TTF4[(H3O)M(C2O4)(3)]C5H5N where M = Ga3+, Cr3+ or Fe3+

J MAGN MAGN MATER 272-76 (2004) 1062-1064

Authors:

AI Coldea, AF Bangura, J Singleton, A Ardavan, A Akutsu-Sato, H Akutsu, SS Turner, P Day

Abstract:

We report high-field magneto transport measurements on beta''- BEDT-TTF4[(H3O)M(C2O4)(3)]C5H5N, where M = Ga3+, Cr3+ or Fe3+. In spite of the differing M ions, these compounds have very similar Fermi surfaces. We observe four distinct Shubnikov-de Haas frequencies, corresponding to four Fermi-surface pockets; the frequencies exhibit the additive relationship expected for a compensated semimetal. The compounds show paramagnetic behaviour and no superconductivity down to 0.5 K, in contrast to other materials of the same family with different solvent molecules. (C) 2003 Elsevier B.V. All rights reserved.
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