Experimental Study of the Thermal Transport in $CsNiF_3 - An S = 1$ Quantum Chain

The heat transport in a single-crystal of $CsNiF_3$ has been performed in the temperature range from 2 K to 7 K in a zero magnetic field, B = 0, as well as in sufficiently large magnetic fields, B = 6 T and 9 T, inducing the ferromagnetic ground state along the hard c-axis. $CsNiF_3$ represents an S = 1 quasi-one-dimensional XY ferromagnet with the intra-chain exchange coupling $J//k_{B}$ ≈ 24 K, single-ion anisotropy $D/k_{B}$ ≈ 8 K, and ordering temperature $T_{N}$ = 2.7 K. Comparison of the phonon and magnon velocities suggests that phonons are the main heat carriers in this magnetic insulator. The thermal conductivity in B = 0 was analysed in the frame of a standard Debye model. The temperature dependence of the effective phonon mean free path was calculated from the experimental data, and the enhancement of the phonon mean free path in B ≠ 0 was obtained, indicating that magnons act as scattering centers for phonons.