Long-range magnetic order and interchain interactions in the S=2chain systemMnCl3(bpy)...

Acompoundwithveryweaklyinteractingchains,MnCl3(bpy),hasattractedagreatdealofat-tentionasapossibleS=2Haldanechain.However,long-rangemagneticorderofthechainsbelow11.5KpreventstheHaldanegapfromdeveloping.Usingafour-sublatticemodel,theantiferromag-neticresonance(AFMR)spectrumuptofrequenciesof1.5THzandmagneticfieldsupto50TiswelldescribedwhentheinterchaincouplingisindeedquitesmallbuttheDzaloshinskii-Moriyainteractionproducedbybrokeninversionsymmetryissubstantial(0.12meV).Inaddition,thean-tiferromagnetic,nearest-neighborspininterchaininteractionassumesavalue(3.3meV)whichissignificantlystrongerthanpreviouslyreported.TheexcitationspectrumofthisS=2compoundiswell-describedbya1/Sexpansionabouttheclassicallimit.