Abstract
We have studied magnetic ordering in polycrystalline erbium at high pressures up to 32 GPa and low temperatures up down to 10 K using neutron diffraction techniques at the Spallation Neutron Source at Oak Ridge National Laboratory, USA. For the hexagonal close-packed (hcp) phase, strong nuclear and magnetic satellite intensities permit a simultaneous refinement of the nuclear and magnetic structures. At 1 GPa of applied pressure, a modulation vector q=γc^* with γ≈2/7 for the c-axis modulated and cycloidal phases is consistent with prior single-crystal studies at low pressures. At 6.7 GPa in the hexagonal closed pack (hcp) phase, we find γ≈0.31, indicating a reduction in the period of the magnetic structure with respect to the crystal lattice. The magnetic ordering temperature at 6.7 GPa is slightly above 60 K. At 32 GPa in the double hexagonal close-packed phase, the reversible appearance of a magnetic reflection scattering constrains the magnetic ordering temperature to 25±5 K. Our studies demonstrate that magnetic ordering persists in the high-pressure double hexagonal close-packed phase up to the highest pressure reached in neutron diffraction studies of 32 GPa in erbium.
