Antiferromagnetic phase in β′ - (BEDT-TTF)2 ICl 2 under pressure as seen via C13 NMR

Abstract

We assessed carbon-13 nuclear magnetic resonance (C 13 NMR) measurements of the layered organic salt β′ - (BEDT-TTF)2 ICl 2, which exhibits antiferromagnetic transition at ambient pressure and 22 K and superconductive transition at 8.2 GPa and 14.2 K (the highest known superconductive transition temperature among organic superconductors). By analyzing the C 13 NMR spectrum with the tensor, we determined the antiferromagnetic moment of this salt to be μB per dimer at ambient pressure, strongly indicating that this salt is a dimer Mott insulator. From NMR measurements under pressure, we found that the structure of the antiferromagnetic phase changed at 0.6 GPa. The moment of this antiferromagnetic phase was estimated to be 0.47 μB per dimer at 0.6 GPa and 26 K. In addition, applying pressure rapidly decreased the spin susceptibility in the paramagnetic state, and the pressure dependence of TN showed anomalous behavior consistent with theoretical proposals, including dimensional crossover. © 2010 The American Physical Society.