J. Phys. IV France
Volume 114, April 2004
Page(s) 285 - 287

J. Phys. IV France
114 (2004) 285
DOI: 10.1051/jp4:2004114060

The effect of magnetic ions and disorder on superconducting $\beta{''}$-(BEDT-TTF) 4[ (H 3O)M(C 2O 4) 3] $\cdot$ C 6H 5NO 2 salts, where M = Ga and Cr

A.F. Bangura1, 1, A.I. Coldea1, A. Ardavan1, J. Singleton2, A. Akutsu-Sato3, H. Akutsu3 and P. Day3

1  Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK
2  National High Magnetic Field Laboratory, Los Alamos National Laboratory, TA-35, MS-E536, Los Alamos, NM 87545, USA
3  Davy-Faraday Research Laboratory, The Royal Institution, 21 Albemarle Street, London W1S 4BS, UK

We report magnetotransport measurements performed in magnetic fields of up to 33 T and at low temperatures (0.45 K <T <4.2 K) on two iso-structural superconducting charge-transfer salts, $\beta^{''}$-(BEDT-TTF) 4[ (H 3O) M(C 2O 4) 3] $\cdot$ C 6H 5NO 2, where the 3d metal ion M is either non-magnetic Ga 3+ or magnetic Cr 3+. 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 $1.2 \pm
0.2~m_{e}$ to $2.2 \pm 0.3~m_{e}$ and reducing the superconducting critical temperature from Tc  $\approx$ 8 K to Tc  $\approx$ 5 K. Key words. organic superconductors-quantum oscillations.

© EDP Sciences 2004