All ETDs from UAB

Advisory Committee Chair

Yogesh K Vohra

Advisory Committee Members

Cheng-Chien Chen

Antonio M Dos Santos

Nenad Velisavjevic

Mary Ellen Zvanut

Document Type


Date of Award


Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences


Neutron diffraction experiments on rare earth metals dysprosium (Dy) and holmium (Ho) have been performed to high pressure and low temperature using novel large-volume diamond anvil cells (DAC) at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). Neutron diffraction is necessary to determine the magnetic structure of these materials due to the intrinsic spin property of neutrons. High pressure neutron diffraction experiments have historically been limited in the pressure and temperature range achievable due to the use of Paris-Edinburgh (PE) press, however new advances in large volume diamond anvil cells allows a much broader range of pressures and temperatures than before. Neutron diffraction data have been taken at two different wavelengths in order to observe peaks in a wide-range of momentum transfer of 0.63 Å-1 to 13.5 Å-1 (interplanar d-spacings in the range of 10 Å to 0.5 Å), arising from the nuclear lattice long-range magnetic ordering. These techniques, when combined and with the addition of high-pressure x-ray diffraction data have revealed the crystal phases of Dy, Ho, and erbium (Er) to pressures up to 280 GPa as well as the magnetic structures present in the crystalline phases of Dy and Ho at low temperatures down to 10 Kelvin and from ambient pressure to 22 GPa and 31 GPa, respectively. The high-pressure structural data have confirmed the existence of an orthorhombic phase with 16 atoms (oF16) in heavy rare earth metals reinforcing their similarity with the structural trends in actinide iii metals. The magnetic structural refinements have yielded complex magnetic structures in ambient and high-pressure phases of heavy lanthanides with magnetic propagation vectors that are commensurate as well as incommensurate with the lattice derived from x-ray structural investigations. The incommensurate and commensurate propagation vectors as a function of pressure and temperature in heavy lanthanides will provide a critical test for validation of future first principles calculations on magnetic ordering in these materials.



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