NMR Investigation of the Organic Conductor lambda-(BETS)2FeCl4

Abstract

The two-dimensional organic conductor lambda-(BETS)2FeCl4 has an unusual phase diagram as a function of temperature and magnetic field that includes a paramagnetic metal (PM) phase, an antiferromagnetic insulating (AFI) phase, and a field-induced superconducting phase [S. Uji, H. Kobayashi, L. Balicas, and James S. Brooks, Adv. Mater. 14, 243 (2002), and cited references]. Here, we report a preliminary investigation of the PM and AFI phases at 9.0 T over the temperature range 2.0-180 K that uses proton NMR measurements of the spectrum, the spin-lattice relaxation rate (1/T1), and the spin echo decay rate (1/T2). The sample is asmall single crystal whose mass is approximately 3 micrograms (approximately 2E16 protons). Its small size creates several challenges that include detecting small signals and excluding parasitic proton signals that are not from the sample [H. N. Bachman and I. F. Silvera, J. Mag. Res. 162, 417 (2003)]. These strategies and other techniques used to obtain viable signals are described.

Submitted for publication in Advances in Magnetic Resonance as part of the special volume for the proceedings of the Colloque AMPERE 2003, dedicated to the 70th birthday of Robert Blinc