Award Date

5-1-2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Committee Member

Andrew Cornelius

Second Committee Member

Ashkan Salamat

Third Committee Member

Oliver Tschauner

Fourth Committee Member

Paul Forster

Number of Pages

132

Abstract

Many intermetallic solids containing elements from the rare earth series show interesting and unusual behavior associated with 4f electrons. This behavior includes unusual magnetic order, strongly correlated electrons, intermediate valence, heavy fermions, the Kondo effect, superconductivity, and non-Fermi liquid (NFL) to name a few. When long range magnetic order is suppressed to T = 0 K by the application of an external tuning parameter such as pressure, magnetic field, or chemical doping, a quantum critical point (QCP) appears in which strong quantum fluctuations give rise to many of the mentioned unusual properties.

Most of the past studies on unusual 4f materials focus on those containing Ce and Yb with less work on Eu. However, europium intermetallic compounds also show a wide range of physical and magnetic properties as well as intermediate valences between the Eu2+ and Eu3+ configurations. A europium ion can be either divalent (Eu2+:S = 7/2, L = 0, J = 7/2) or trivalent (Eu3+: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 moment. This has profound consequences on both the physical and magnetic properties of europium materials, especially under pressure. This dissertation studies three europium compounds, EuMn2Si2, EuCo2Si2, and Eu5In2Sb6, in which europium exhibits mixed valence states. Samples were obtained through collaboration with Los Alamos National Laboratory. Specific heat and magnetic susceptibility measurements were performed at UNLV. High pressure powder X-ray diffraction (HPXRD) and high pressure X-ray resonant emission spectroscopy (HPRXES) were performed at Argonne National Laboratory at the High Pressure Collaborative Access Team (HPCAT). Analysis of the data from these experiments furthers the understanding of the valence behavior of europium in these materials and gives insight to future theoretical predictions of critical behavior of mixed valence systems.

Keywords

Europium; High pressure; Magnetic susceptibility; Specific heat; Valence

Disciplines

Condensed Matter Physics

Language

English


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