McClintock, Peter V. E. and Rosenberg, H. M.
(1968)
*The effect of a magnetic field on the thermal conductivity of paramagnetic crystals : cerium ethylsulphate.*
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 302 (1470).
pp. 419-436.
ISSN 1364-5021

## Abstract

The thermal conductivity of crystals of concentrated cerium ethylsulphate has been measured in the range 1 to 4.58 OK and in magnetic fields of up to 53 kG. In zero field there is a marked anomaly at 2.5 K in the variation of conductivity with temperature. Owing to the anisotropy of the g-values the magnetic field dependence of the thermal resistivity at constant temperature depends on the field direction; with the field parallel to the hexagonal axis, a maximum occurs in the resistivity which moves roughly linearly with temperature, and in very high fields it is always less than in zero field; with the field applied in the perpendicular direction a resistivity maximum is only observed above 2 OK, and in the highest available field it is always much greater than in zero field. These results are explained by assuming that direct process phonon-spin interactions scatter certain bands of phonons whose frequency depends on the separation of the energy levels produced by the applied magnetic field. A statistical theory is used to determine the relative populations of the energy levels in the calculation of the thermal resistivity. It is assumed that the spin-phonon absorption lineshape is Gaussian. By fitting the theory to the experimental data, approximate values of the spinlattice coupling constant, the linewidth of the transitions and the mean free paths for boundary and point-defect scattering are obtained.