Local Spin Resonance and Spin-Peierls-Like Phase Transition in a Geometrically Frustrated Antiferromagnet
17 April 2000
Using inelastic magnetic neutron scattering we have discovered a localized spin resonance at 4.5 meV in the ordered phase of the geometrically frustrated cubic antiferromagnet ZnCr sub 2 O sub 4. The resonance develops abruptly from quantum critical fluctuations upon cooling through a first order transition to a co-planar antiferromagnet at T sub c = 12.5(5) K. We argue that this transition is a three-dimensional analogue of the spin-Peierls transition.