Spontaneous strain in ferroquadrupolar phase of TmAu₂

We present the results of a study of the spontaneous strain accompanied by a ferroquadrupolar ordering in TmAu₂. The strain has been investigated by means of thermal expansion, magnetostriction, and neutron diffraction measurements on a single crystalline TmAu₂. In the ferroquadrupolar ordered phase, the strain shows a strong enhancement by applying magnetic field. This implies that structural orthorhombic domains caused by the ferroquadrupolar ordering are transformed into a single-domain structure by a magnetic field.