Near-zero thermal expansion in magnetically ordered state in dysprosium (Dy)

Figure caption: An X-ray diffraction pattern for Dy at high pressures and low temperatures utilized in the measurements of thermal expansion.
Figure caption: An X-ray diffraction pattern for Dy at high pressures and low temperatures utilized in the measurements of thermal expansion.

Rare earth elements are extensively utilized in a variety of applications including strong permanent magnets, lasers, lighting industry, automobiles, nuclear industry, and medicine. With one of the highest intrinsic magnetic moments (10.6 Bohr Magnetron) among the heavy rare earth elements, Dy exhibits a rich magnetic phase diagram under high-pressure and low-temperature conditions. The hexagonal close-packed (hcp), alpha-Samarium (α-Sm), and double hexagonal close-packed (dhcp) phases are observed to be stable in Dy under high-pressure and low-temperature conditions. Dy is known to undergo magnetic ordering below 176 K at ambient pressure with magnetic ordering Néel temperature (TN) that changes rapidly with increasing pressure. A research team using HPCAT facility found that Dy has near-zero thermal expansion in the magnetically ordered state and normal thermal expansion in the paramagnetic state for all the three known high pressure phases (hcp, α-Sm, and dhcp) to 35 GPa. The connection between lack of thermal expansion and magnetic ordering is likely a universal phenomenon for rare earth metals under extreme conditions. More in Hope et al, Cogent Phys., (2017)