Low-temperature thermal expansion of γ-irradiated ruby

Measurements of the low-temperature thermal expansion of γ-irradiated rubies have been made with use of a three-terminal capacitance dilatometer. The data exhibit a positive Schottky-type anomaly at ∼3.9 K, not present in the data obtained for a pure Al2O3 sample, and this contribution to the thermal expansion has been tentatively attributed to the presence of Cr2+ (produced by γ irradiation) exhibiting a large positive magnetic Grüneisen coefficient as predicted by a dynamic Jahn-Teller model.