On the influence of heat transport on low- frequency paramagnetic spin—Lattice relaxation experiments

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 τ_abs, related to the maximum in the absorption curve, a temperature dependence $\text{τ}{}_{\mathrm{abs}}{}^{\mathrm{\alpha }}\text{T}{}^{\mathrm{-\alpha }}$ with 1 < α < 6 has been found frequently, accompanied sometimes with a jump at the helium-transition temperature T_λ. 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, τ_abs(T) (related to the maximum of the calculated absorption curve) can be described roughly as mentioned above with a jump at T_γ.