Dynamics of the frustrated spin in the low dimensional magnet Co3(OH)2(C4O4)2.

We describe powder inelastic neutron scattering experiments on a porous coordination polymer Co3(OH)2(C4O4)2, which has two different ordered magnetic phases known to display spin frustrated behaviour, resulting in an idle-spin phase. The moment on each ion is represented by an effective total angular moment J(eff ) = ½. A non-dispersive magnetic mode was observed in the idle-spin phase which is described by a simple dimer model that assumes ΔJ = 0. The excitation was found to persist well above the long range ordering temperature into the paramagnetic region. A combination of frustration, the J(eff) = ½ and low dimensionality may induce these quantum phenomena.