Nuclear Spin-Lattice Relaxation Associated with Two-Magnon Bound States in S=1⁄2 Ferromagnetic Ising-Like Linear Chain

Abstract

In the S=1⁄2 ferromagnetic Ising-like linear chain, it is expected that the two-magnon bound states are excited thermally together with the single magnons. A new mechanism of the nuclear spin-lattice relaxation in this system is studied. It is associated with the scattering of a spin wave and a two-magnon bound state accompanied by the nuclear-spin flip. The relaxation rate is derived under the assumption that the two-magnon bound state behaves like a boson. It proves that the second-order exchange-scattered process makes a significant contribution to the total relaxation rate. The calculated relaxation times for proton and ³⁵Cl in one-dimensional Ising-like system; [(CH₃)₃NH]CoCl₃·2H₂O agree well with the zero-field experimental data in the order of magnitude as well as in the qualitative nature of the temperature dependence.