Investigating complex, marginal and exotic magnetic ordering in rare-earth based materials

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Three primary themes will be the focus of the next five years of my research program: (1) Discovering new technetium-based intermetallic compounds (2) Exploring exotic magnetic ordering in europium-based intermetallic compounds (3) Investigating valence instabilities and magnetic ordering in ytterbium-containing systems. The first theme will involve the creation of a new facility to handle technetium and prepare single-crystal samples using it. Technetium is remarkable. It is the lightest element that lacks a stable isotope. Indeed it is the only radioactive element in the main s,p,d block of the periodic table. It sits directly below manganese and shares its half-filled d5 electronic configuration, opening the possibility of 4d magnetism. Some compounds, notably oxides and halides are known to be magnetic, and some metallic systems are superconducting, but very few of its intermetallic compounds have ever been prepared and fewer still have been investigated for magnetism. While it unlikely that any compound of technetium will see direct applications (its 6-day parent 99Mo is a key medical isotope, used in the diagnosis of heart problems and cancers) the knowledge gained will lead to a better understanding of magnetic systems. The second theme is Eu-based materials. Recent theoretical and experimental discoveries of topological semi-metals (TSM) and Weyl semi-metals are opening exciting frontiers of science at the boundaries of materials science and magnetism. The hope is that understanding the basic principles of TSM and WSM systems will deliver new materials platforms for photodetection, spintronics and quantum computing. I will be working with teams from the AmesLab in Iowa studying a wide range of Eu-based materials using Mössbauer spectroscopy and neutron diffraction. We have already identified some materials that have potential as magnetic refrigerants offering greenhouse gas (GHG) free refrigeration and have several more systems that we are studying. The third theme is Yb-based materials. Ytterbium exhibits a significant valence instability that leads to a rather fragile magnetic moment. We will combine 170Yb Mössbauer spectroscopy with neutron diffraction to investigate these systems. In addition, several Yb compounds show promise for thermoelectric power generation (direct conversion of waste heat into electricity). Many rely on the presence of “rattlers”, weakly bound rare-earth or alkaline earth metals. There are few direct ways to investigate these almost-isolated atoms, however the digital time-differential perturbed angular correlation (TDPAC) spectrometer that we designed and built is perfect for the project. We will work with teams from Italy and the US on these projects.