Magnetic Neutron Scattering from a Nearly Ideal One-Dimensional Antiferromagnet

Abstract

We have carried out a detailed investigation of the linear chain antiferromagnet, (CD3)4N MnCl3 using elastic and inelastic neutron scattering techniques. The MnCl3 chains in this compound are found to exhibit purely one-dimensional paramagnetic behavior down to at least 1.1°K, with no evidence for the onset of three-dimensional order. The interactions between Mn2+ ions along the chain are such that a molecular field theory would predict an ordering at 76°K. The quasielastic measurements, which yield ∫dωS(Q,ω)=1/N〈S(−Q,0)S(Q,0)〉 show planes of scattering intensity perpendicular to the chain axis. From the thermal evolution of the planar scattering, the temperature dependence of the correlation length has been obtained and is compared with the theory for the classical Heisenberg linear chain antiferromagnet with which it shows very good agreement. The inelastic measurements show that at 4.4°K for q and ω≠0, S(q, ω) may be described by long-lived spin waves which accurately follow the dispersion relation ℏω=6.1 sin qzc/2 (meV) over the entire one-dimensional Brillouin zone. As the temperature is increased these ``spin waves'' weaken in intensity and broaden asymmetrically, with the scattering increasing on the low-energy side.