SR study on the spin singlet state in the S = 1/2 cluster magnet GaNb 4S8

Abstract

GaNb4S8 is a S = 1/2 Nb4-cluster magnet exhibiting a structural phase transition at Ts = 32 K. We have investigated the magnetic ground state of the compound by means of the zero-field (ZF) and the longitudinal-field (LF) SR techniques. In the ZF-SR spectra, no muon spin precession was observed below Ts, revealing an absence of magnetic long-range orders. Instead, an stretched exponential relaxation was observed, which remains under the LF up to 3950 G. The field dependence of the relaxation rate obeys the Redfield's equation, indicating that a dynamic component of electronic spin fluctuations is dominant below T s. These SR results can be understand as sporadic dynamics of spin fluctuations in a spin singlet sea and support the spin singlet state of GaNb4S8 due to the formation of Nb8 octamer from two Nb4 tetramers. © 2010 IOP Publishing Ltd.