NMR investigation of the organic conductor λ-(BETS)2FeCl4

The two-dimensional organic conductor λ-(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, J. S. Brooks: Adv. Mater. 14: 243, 2002). Here, we report a preliminary investigation of the PM and AFI phases at 9 T over the temperature range of 2.0–180 K that uses proton nuclear magnetic resonance measurements of the spectrum, the spin-lattice relaxation rate 1/T1, and the spin echo decay rate 1/T2. The sample is a small single crystal whose mass is about 3 μg (approximately 2·1016 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, I. F. Silvera: J. Magn. Reson. 162: 417, 2003). These strategies and other techniques used to obtain viable signals are described.