Thermal expansion anomalies in dysprosium

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Abstract
The temperature dependence of the thermal expansion coefficient along the hexagonal c axis of single-crystal dysprosium has been investigated in the vicinity of the phase transitions and near the temperatures where the periodicity of the helix spin structure is commensurate with that of the crystal lattice. No length discontinuity of more than 2*10-7 cm has been observed at the Neel temperature. On cooling the sample, a discontinuity in the relative length change of about Delta L/L=5*10-5 has been discovered at a temperature of about 171+or-1K. Its nature is attributed to a transition from a vortex structure to helical long-range order. At the Curie point the temperature and the magnitude of the length discontinuity depend on the thermal history of the sample. No anomalous changes in the thermal expansion coefficient have been observed at the temperatures where magnetic and crystalline structures are commensurate.