We demonstrate that local modulations of magnetic couplings have a profound effect on the temperature dependence of the relaxation rate of optical magnons in a wide class of antiferromagnets in which gapped excitations coexist with acoustic spin waves. In a two-dimensional collinear antiferromagnet with an easy-plane anisotropy, the disorder-induced relaxation rate of the gapped mode, Gamma_imp=Gamma_0+A(TlnT)^2, greatly exceeds the magnon-magnon damping, Gamma_m-m=BT^5, negligible at low temperatures. We measure the lifetime of gapped magnons in a prototype XY antiferromagnet BaNi2(PO4)2 using a high-resolution neutron-resonance spin-echo technique and find experimental data in close accord with the theoretical prediction. Similarly strong effects of disorder in the three-dimensional case and in noncollinear antiferromagnets are discussed.
@article{arxiv.1206.4690,
title = {Lifetime of Gapped Excitations in a Collinear Quantum Antiferromagnet},
author = {A. L. Chernyshev and M. E. Zhitomirsky and N. Martin and L. -P. Regnault},
journal= {arXiv preprint arXiv:1206.4690},
year = {2012}
}
Comments
4.5 pages + 2.5 pages supplementary material, published version