Magnetic ordering in a distorted S= pyrochlore antiferromagnet

In this work we explore the structural and magnetic properties of a distorted S = 1/2 pyrochlore antiferromagnet: the mineral clinoatacamite, gamma-Cu-2(OH)(3)Cl. DC magnetization and specific heat data demonstrate its high degree of frustration (\theta(w)\/T-c = -30) and reveal that the Neel groundstate, observed below T-c similar or equal to 6K, features extensive quantum fluctuations. Inelastic neutron scattering is used to quantify the characteristic energy scales of the system. (C) 2004 Elsevier B.V. All rights reserved.