J. Phys. IV France 114 (2004) 199
DOI: 10.1051/jp4:2004114044

The effect of pressure on the phase diagram of the magnetic field-induced superconducting state of -(BETS) ₂FeCl ₄

L. Balicas^{1, 1}, V. Barzykin², K. Storr^{1, 3}, J.S. Brooks¹, M. Tokumoto⁴, S. Uji⁵, H. Tanaka⁶, H. Kobayashi⁶ and A. Kobayashi<sup>7

1</sup>  National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32306, USA
²  Department of Physics, University of Tennessee, Knoxville, TN 37996-1200, USA
³  Physics Department, Florida A&M University, Tallahassee, FL 32307, USA
⁴  Nanotechnology Research Institute, Tsukuba, Ibaraki 305-8568, Japan
⁵  National Research Institute for Metals, Tsukuba, Ibaraki 305-0003, Japan
⁶  Institute for Molecular Science, Okazaki, Aichi 444-8585, Japan
⁷  Research Centre for Spectrochemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan

Abstract
We report the effect of a small hydrostatic pressure p 1.4 kBar on the temperature-magnetic field phase diagram of the organic conductor -(BETS) ₂FeCl ₄. At zero field a first-order superconducting ( 5.6 K) to antiferromagnetic insulator transition ( 4 K) is observed. The close proximity between both phases is suggestive of an unconventional superconducting pairing mechanism. Furthermore, the transition temperature towards the field-induced superconducting state (FISC), as well as its concomitant upper critical field, is found to increase by a factor of 33 %. The phase diagram of the FISC state for both p = 1 Bar and 1.4 kBar are well described in terms of the Jaccarino-Peter effect if the quasiparticle nature of the charge carriers is taken into account. Key words. Organic conductors - magnetism - superconductivity.

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