Rare Earth Metal Erbium Under High Pressures and Low Temperatures

The rare earth metal erbium has gained the attention of physicists for its unique characteristics of nearly zero thermal expansion at low temperatures and large magnetic dipole moment, making this material an excellent candidate for permanent magnets at low temperatures. Erbium metal was studied under high pressures up to 65 GPa and low temperatures down to 20 K in a diamond anvil cell by X-ray diffraction (XRD) at HPCAT, Advanced Photon Source, Argonne National Laboratory. Pressure was monitored during the experiment through a combination of ruby fluorescence and the measured volume of a copper pressure marker at high pressures and low temperatures. The XRD data was analyzed with GSAS-II to identify lattice parameters for both copper and erbium. The erbium sample data was analyzed at pressures of 1, 20, 40, 50, and 65 GPa and temperatures between 295 K and 20 K for each pressure point. The analysis of thermal expansion data for the hexagonal close packed (hcp) phase and the double hexagonal close packed (dhcp) phase of erbium confirm the nearly zero thermal expansion characteristics of this material to the lowest temperature of 20 K. The x-ray diffraction data is complemented by the neutron diffraction study of magnetic ordering at the SNAP beamline at the Spallation Neutron Source, Oak Ridge National Laboratory.