Magnetic excitations in a highly frustrated pyrochlore antiferromagnet

Spins that are coupled antiferromagnetically on the pyrochlore lattice are exposed to a high degree of geometrical frustration, resulting in the general absence of long-range order at all temperatures. We have investigated the inelastic response of the pyrochlore ${\mathrm{CsNiCrF}}_6$ using neutron scattering. At positions where strong magnetic diffuse scattering has been observed we find a strong elastic signal, together with an unusual wing of inelastic scattering that is present even below the spin-glass transition of ${\mathrm{CsNiCrF}}_6$. This indicates that while some of the magnetic fluctuations are being frozen out, others persist on a scale well in excess of the apparent spin-freezing temperature.