Technical Report of ISSP Ser. A: Number 3211

Abstract

Spin dynamics of hexagonal ABX3-type quasi-one-dimensional antiferromagnet CsVCl3 is investigated by means of inelastic neutron scattering technique. In good qualitative agreement with a recent spin-wave calculation including higher-order terms, large scattering cross-section arising from two-magnon excitations is observed at one-dimensional antiferromagnetic zone-center. In addition, spin-wave excitations between the chains were measured precisely and it was revealed that the spin-wave dispersion curves are modified in energy and in intensity on account of anticrossing between the one-magnon branches and two-magnon continuum. These results demonstrate that anharmonic terms are important in the spin dynamics of CsVCl3 even at low temperatures. Temperature dependence of the magnetic excitations was also measured, and it was found that far above the Neel temperature two-magnon process gave considerable contribution to inelastic spectrum.

六方晶ABX3型準1次元反強磁性体CsVCl3のスピン動力学を非弾性中性子散乱手法により検討した。高次数項を含む最近のスピン波計算との定性的な良い一致において、2マグノン励起から起きる大きな散乱断面を1次元反強磁性晶帯中心に観測した。さらに、チェーン間のスピン波励起を精密に測定し、スピン波分散曲線は1マグノン分枝と2マグノン連続体の間の反交差性によってエネルギーと強度を修正されることを明らかにした。これらの結果は非調和項が低温においてもCsVCl3のスピン動力学では重要であることを証明している。また、磁気励起の温度依存性を測定し、Neel温度のはるか高温で2マグノンプロセスが非弾性スペクトルにかなり寄与していることが分かった。