Commensurate turn angle effects in single-crystal antiferromagnetic dysprosium

Abstract

The temperature dependences of the c axis thermal expansion and elastic constant c44 have been measured in single-crystal samples of dysprosium between the Neel temperature TN and Curie temperature TC. Anomalous behaviour is observed at several temperatures in the range TC<T<TN, and the anomalies are attributed to the occurrence of helical turn angles which are commensurate with the periodicity of the basal plane hexagonal crystal structure. The mechanisms which may be responsible for this behaviour are discussed in the light of the model employed to describe similar effects previously observed in holmium at approximately 24K. It is proposed that the anisotropy leads to instabilities in the magnetic structure whenever the commensurate turn angle condition is met.