Report on Malcolm F. Nicol Graduate Scholar Research Activities
Mixed valence 4-f electron systems have been of great interest recently. Particular focus has been on rare-earth intermetallic compounds containing europium. They exhibit a range of properties as well as intermediate valences associated with the transition from the Eu2+ configuration to the Eu3+ configuration. A Eu ion can be either divalent (Eu2+: 4f7, S = 7/2, L = 0, J = 7/2) or trivalent (Eu3+:4f6, S = L = 3, J = 0). Divalent europium has a larger volume and magnetic moment (7 μB/Eu), while trivalent europium has a smaller volume and no magnetic moment1.
In some Europium compounds, the valence state becomes unstable and can change from an almost divalent state at high temperatures to a trivalent one at low temperatures with the probability decreasing with temperature. This valence transition is similar to the Kondo effect, where the magnetic moment from localized f electrons is quenched. For rare-earth and actinide compounds, the competition between the Kondo effect and Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction induces phenomena such as heavy fermion, unconventional superconductivity, and non-Fermi liquid behavior. Many Ce- and Yb-based heavy fermion compounds have been extensively examined. My current work focuses on examining potential Eu-based heavy fermion compounds.
Much of the time spent while a Malcolm F. Nicol Graduate Scholar was exploring various high-pressure techniques and researching possible projects that lead me to the study of Europium intermetallic systems. High-pressure X-ray diffraction experiments of EuMn2Si2 and EuCo2Si2 have been performed at Argonne National Laboratory at the Advanced Photon Source at sector 16 of the High Pressure Collaborative Access Team (HPCAT). A Princeton symmetric type diamond anvil cell (DAC) loaded with ruby for pressure measurement and neon as a pressure-transmitting medium were used for these experiments. Heat capacity and magnetization measurements were performed in a Quantum Design PPMS system at UNLV. Future temperature dependent measurements of Europium valence under pressure are planned to be performed using Resonant Inelastic X-ray Scattering at the APS.