Technical Report of ISSP Ser. A: Number 2774

Abstract

Magnetic excitations of CsMnI3, a quasi-one-dimensional Heisenberg antiferromagnet with S = 5/2, have been measured by means of inelastic neutron scattering. Magnetic excitations in the low temperature phase are in good agreement with the predictions of the conventional linear spin-wave theory. In particular, in accordance with the linear spin-wave theory, three separate modes were found at Q = (0,0,1) instead of a threefold degenerate mode as seen in CsNiCl3 (S = 1). It confirms that the spin dynamics of the integer spin value system are very different from those of the half-integer spin value system, even in their three-dimensionally ordered phase. Magnetic excitations in the intermediate phase have been also studied and it is found that the excitations were similar to those in the low temperature phase, except some overdamped intensities at certain reciprocal points. These intensities can be associated to the slow rotational motions of the spins around the c-axis.

S=5/2の準1次元ハイゼンベルク反強磁性体CsMnI3の磁励を非弾性中性子散乱によって測定した。低温相の磁励は通常の線形スピン波理論の予測とよく一致した。とくに、線形スピン波理論によって、Q=(0、0、1)で3分離モードを見出した。このことは、3次元の整列相であっても、整数スピン系のスピン力学が半整数スピン系の力学と異なることを示している。中間相の磁励についても調べ、その磁励が、いくつかの相反点での過剰減衰強度を除いては、低温相のものと同じであることがわかった。これら強度はC軸まわりのスピンのゆるやかな回転運動に関係づけられる。