Study of thermal conductivity due to spins in one-dimensional spin systems AFeX₃ (A=Rb, Cs; X=Cl, Br)

Large contributions of the thermal conductivity due to spins, κ_spin, in low-dimensional spin systems are expected to be utilized as highly thermal-conducting materials. Single crystals of one-dimensional spin systems RbFeCl₃ with ferromagnetic (FM) chains and CsFeBr₃ with antiferromagnetic (AF) chains have been prepared in order to observe the contribution of κ_spin to the thermal conductivity. The thermal conductivity parallel to spin chains along the c-axis, κ//_c, of RbFeCl₃ has been found to be enhanced around 3 K and 10 K by the application of magnetic field. In the thermal conductivity perpendicular to the c-axis, κ⊥_c, of RbFeCl₃, on the other hand, only one peak around 3 K has been found to be enhanced by the application of magnetic field. Since κ⊥_c is mainly owing to the thermal conductivity due to phonons, κ_phonon, it has been concluded that the peak of κ//_c around 10 K in magnetic fields is due to the contribution of κ_spin. For CsFeBr₃, it has been found that κ//_c shows two peaks around 3 K and 25 K while κ⊥_c shows one peak around 12 K in zero field. This indicates that there is a marked contribution of κ_spin to κ//c. However, the details are not yet clear. It has been found that κ//c in RbFeCl₃ is enhanced by the application of magnetic field while κ//_c in CsFeBr₃ is suppressed. The difference may be due to the difference between FM chains in RbFeCl₃ and AF chains in CsFeBr₃.