The thermal conductivity of Ni 2 + doped KMgF 3 in a magnetic field at low temperatures: the effect of single ions and coupled pairs

Abstract
The thermal conductivity between 0.4 and 4.2 K and in magnetic fields up to 50 kOe of KMgF3 doped with Ni2+ has been measured. The results are analysed to give values of the average spin-lattice coupling constants ( xSl) for the Ni2+ ion. These are in agreement with values calculated using the magneto-elastic constants (GX1 and 6r44) derived from acoustic paramagnetic resonance (a.p.r.) experiments. Below IK the thermal resistivity as a function of magnetic field shows a number of anomalies, for which possible causes are discussed; it is concluded that they result from phonon interactions with exchange-coupled pairs of Ni2+ ions. Such pairs are also observed in a.p.r. experiments.

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