Studies of magnetic behavior of spin-1/2 frustrated system Hg2Cu2F6S

A geometrically frustrated spin (s)=1/2 system Hg2Cu2F6S with the pyrochlore structure has been studied by 19F-NMR. Measurements of the magnetic susceptibility χ and specific heat C and neutron structure analyses have also been carried out. The value of the Weiss temperature estimated from the temperature (T) dependence of χ is found to be ∼100 K, indicating that the exchange interaction among the Cu spins is antiferromagnetic. The system does not exhibit a lattice distortion and remains paramagnetic, at least, down to 2.4 K. It indicates that the system is a good candidate of 3-dimensional frustrated spin systems. With decreasing T, the Knight shift of the 19F-NMR decreases after having a broad maximum at ∼80 K, indicating that the upturn of χ observed at low T with decreasing T is not intrinsic