Methods of dilatometric investigations under extreme conditions and the case of spin-ice compounds

Abstract

We give an overview on how dilatometric methods have been developed in the last decade. The concept of capacitive dilatometry was successfully adapted to dilution refrigerators with a resolution of 10−9. Miniaturized dilatometers with an overall diameter of 18 mm or less are optimally suited for measuring longitudinal and transversal components of the striction tensor. Going to another extreme, to the highest (pulsed) fields, optical methods, such as the FBG technology, were developed for investigations up to 100 T.As examples for utilizing dilatometry at low temperatures we show results for the spin-ice materials Dy2Ti2O7 and Ho2Ti2O7. To characterise the magneto-elastic coupling in these materials, we investigated the thermal expansion and magnetostriction between 80 mK and 15 K and in magnetic fields aligned along the [111] direction and found field-induced phases and strong correlations below 500 mK. Our data demonstrate, that the formation of the field-induced phase is strongly influenced by lattice distortions: any change in interatomic distances will result in a variation of the exchange couplings.