Magnetic transitions in dysprosium: a calorimetric study

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Abstract
The nature of the magnetic transitions in high-purity dysprosium has been investigated with a high-resolution microcalorimeter. Single crystals of two purities corresponding to RRR values of 88 (Dy(A)) and 15 (Dy(B)) have been studied. At Tn the authors have observed an energy peak for both materials of 7 J mol-1 extending over a few tenths of a degree. The transition temperatures were 180.6+or-0.1 K for Dy(A) and 178.7+or-0.1 K for Dy(B). A small thermal hysteresis in TN was observed for both materials. The data suggest a weak first-order transition at TN. The first-order nature of the ferromagnetic transition has been confirmed. The latent heat measured was 35+or-2 J mol-1 and 17+or-3 J mol-1 and the transition temperature 91.1+or-0.2 and 90.3+or-0.2 K for Dy(A) and Dy(B) respectively. The latent heats are in fair agreement with calculated values. Commensurate turn-angle effects have been sought in the helical regime. For Dy(A) small energy peaks of 0.2+or-0.1 J mol-1 were observed at 166+or-2 K and 173+or-1 K. The temperatures for the energy changes are close to two of the temperatures of commensurability obtained from neutron diffraction data.