Neutron Diffraction Study of Magnetic Structures in Heavy Lanthanides under Extreme Conditions

Yogesh K. Vohra, University of Alabama at Birmingham (Principal Investigator)

Cheng-Chien Chen, University of Alabama at Birmingham (Co-Investigator)

The lanthanide elements in the periodic table have found applications in diverse fields including catalysis, optical displays, abrasives, neutron absorbers, and as permanent magnets. The crystal structure trends in lanthanide elements under high pressures are well documented, however, there is a lack of data on magnetic ordering under compression that limits our understanding of magnetic phase diagrams in these technologically important materials.  The overall objective of this project is to study magnetic structures in heavy lanthanides under high pressures and low temperatures. The magnetic ordering in lanthanide elements is driven by electron-mediated long-distance exchange coupling between the localized magnetic moments on various lanthanide ionic sites. The magnetic structure determinations in lanthanide elements under high pressures have been largely limited by lack of neutron diffraction data above 10 GPa.. Recent innovations in large volume diamond anvil cells combined with Spallation Neutrons and Pressure Diffractometer (SNAP) at Oak Ridge National Laboratory have resulted in first determinations of magnetic structure in the high-pressure phases of lanthanide elements in the 10-30 GPa pressure range. We propose a comprehensive experiment/theory collaboration in magnetic ordering in heavy lanthanides like Terbium, and Erbiumto 50 GPa and 4K. The goal will be to establish incommensurate and commensurate magnetic structures in the high-pressure phases of heavy lanthanides including alpha-samarium, double hexagonal close-packed, face-centered cubic and distorted face-centered cubic phases. The incommensurate and commensurate propagation vectors magnitudes will be measured as a function of pressure and temperatures and will be compared with the first principles modelling of exchange interactions under extreme conditions. The proposed theory/experiment collaboration in magnetic structures in heavy lanthanides under extreme environments will lead to fundamental understanding of electronic features that gives rise to peaks in paramagnetic spin susceptibility χ (q, T) leading to experimentally observed propagation vectors in neutron diffraction. This project will have a significant impact in workforce development for the DOE national laboratories as graduate students are trained in advanced neutron scattering techniques at a spallation neutron source and in computational tools used to predict structure of magnetic materials.