The spin dynamics of a canted antiferromagnet with a quadratic spin-wave dispersion near \vq=0 is shown to possess a unique signature. When the anisotropy gap is negligible, the spin-wave stiffness \dsw(\vq,B)=(ω\vq−B)/q2 depends on whether the limit of zero field or zero wavevector is taken first. Consequently, \dsw is a strong function of magnetic field at a fixed wavevector. Even in the presence of a sizeable anisotropy gap, the field dependence of both \dsw and the gap energy distinguishes a canted antiferromagnet from a phase-separated mixture containing both ferromagnetic and antiferromagnetic regions.
@article{arxiv.cond-mat/0402633,
title = {Spin Dynamics of a Canted Antiferromagnet in a Magnetic Field},
author = {R. S. Fishman},
journal= {arXiv preprint arXiv:cond-mat/0402633},
year = {2009}
}