Magnetic neutron-scattering studies of RbMnBr3

RbMnBr3 is an XY-like antiferromagnet on a distorted stacked triangular lattice. At low temperatures and fields we show by neutron scattering that there is an incommensurate ordered structure with magnetic Bragg peaks at (h/8±δ,h/8±δ,l) where h and l are odd integers and δ=0.0183±0.0004. At low temperatures, a field of 3 T applied along the a axis produces a first-order phase transition to a commensurate structure corresponding to δ=0, so that …