Extending previous 77Se NMR studies [J. Phys. Soc. Jpn. 72 (2003) 483], the microscopic magnetic properties of superconducting (Tc ≅ 5-6K) λ-(BETS)2GaCl4 [BETS = bis(ethylenedithio) tetraselenafulvalene] have been investigated by 1H NMR in the normal state between 7.1 and 140 K on randomly oriented single crystals. Contrary to almost T-independent 1/(77T1T) of the 77Se NMR, 1/(1T1T) of the 1H NMR shows a significant increase below about 25 K. This quite contrasting low-T behavior in 1/(T 1T) between 77Se and 1H is shown to be explained consistently in terms of the development of antiferromagnetic spin fluctuations of π-electrons, which has already been indicated by the 77Se NMR as a significant low-T decrease in the intrinsic uniform susceptibility χq=0(T) and no concomitant decrease in 1/( 77T1T). In the explanation, it is pointed out that the inter-atomic dipolar interaction with the extended spin polarization of the HOMO plays an important role in the 1H nuclear magnetic relaxation, which has been disregarded in previous 1H NMR studies on related organic conductors.
- Antiferromagnetic spin fluctuations
- BETS compounds
- H NMR
- Organic conductors