Local spin resonance and spin-Peierls-like phase transition in a geometrically frustrated antiferromagnet

摘要

Using inelastic magnetic neutron scattering we have discovered a localizedspin resonance at 4.5 meV in the ordered phase of the geometrically frustratedcubic antiferromagnet $\rm ZnCr_2O_4$. The resonance develops abruptly fromquantum critical fluctuations upon cooling through a first order transition toa co-planar antiferromagnet at $T_c=12.5(5)$ K. We argue that this transitionis a three dimensional analogue of the spin-Peierls transition.