In low-frequency relaxation experiments on paramagnetic crystals, placed in liquid helium, often dispersion- and absorption curves are found, strongly deviating from those following from the thermodynamic theory of Casimir and Du Pré. For the relaxation time τabs, related to the maximum in the absorption curve, a temperature dependence τabs αT-α with 1 < α < 6 has been found frequently, accompanied sometimes with a jump at the helium-transition temperature Tλ. We computed, starting from a model including the heat conduction of lattice and helium bath and a heat resistance from crystal to bath, dispersion- and absorption curves and found that, assuming the direct process for the spin—lattice relaxation, τabs(T) (related to the maximum of the calculated absorption curve) can be described roughly as mentioned above with a jump at Tγ.
Flokstra, J., Gerritsma, G. J., Hartemink, G. A., & van der Marel, L. C. (1974). On the influence of heat transport on low- frequency paramagnetic spin-Lattice relaxation experiments. Physica, 77(1), 99-120. https://doi.org/10.1016/0031-8914(74)90278-X