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Item Broken-symmetry phases of matter and their effects on electronic and magnetic properties(Montana State University - Bozeman, College of Letters & Science, 2023) Peterson, Sean Fahlman; Chairperson, Graduate Committee: Yves U. Idzerda; This is a manuscript style paper that includes co-authored chapters.Physical symmetries inherent to a material are often reflected in its electronic and magnetic properties. The in-plane four-fold rotational symmetry of thin-film ferromagnets inherent to their tetragonal lattice is also exhibited by their cubic anisotropy. The magnetization as a function of applied magnetic field can be calculated via the Stoner- Wohlfarth model. These calculated hysteresis loops were fit to measured hysteresis loops to determine anisotropy constants consistent with known values. An electronic nematic state reduces the in-plane four-fold rotational symmetry of materials by inducing a structural transition from tetragonal to orthorhombic/monoclinic, with two-fold symmetry. This reduced symmetry persists in the electronic thermal transport. Nematicity enhances nearest-neighbor hopping along one axis and reduces it along the other. This results in a deformed Fermi surface compressed (elongated) along the axis of stronger (weaker) electron hopping. This drags van Hove singularities through the Fermi level, affecting quasiparticle lifetimes. Calculating conductivity from the Boltzmann kinetic equation, nematicity enhances thermal transport along one axis and diminishes it along the other. Additionally, s-wave superconductivity coexisting with nematicity creates a feedback on the superconducting gap with a d-wave instability, which can lead to gapless excitations. In the case of weak feedback, nematic superconductors behave like fully-gapped superconductors along both axes, where transport decreases exponentially with temperature. Once gapless excitations form, transport along both axes becomes T -linear at low-T . Similarly, striped antiferromagnetism (AFM2 and AFM3) reduces the rotational symmetry of a square unit cell to a larger two-fold symmetric magnetic cell. Modeling the band structure with a tight- binding model and considering a smaller periodicity in momentum-space, gaps the Fermi surface along one axis. Calculating conductivity reveals diminished transport along one axis and enhanced thermal transport along the other. Considering d-wave superconductivity in this model results in two cases. One has highly anisotropic transport with greatly enhanced T -linear transport along one axis and diminished transport decreasing exponentially with temperature along the other. The second has weakly anisotropic transport with diminished T -linear conductivity along both axes. The symmetry of a material's properties, such as magnetic anisotropy and thermal transport, are intrinsically linked to their crystalline, electronic, and magnetic symmetries.Item Growth and investigation of the Slater-Pauling behavior by x-ray characterization of single crystal bcc Fe x-Mn 1-x thin films on MgO(001)(Montana State University - Bozeman, College of Letters & Science, 2015) Bhatkar, Harshawardhan Ramesh; Chairperson, Graduate Committee: Yves U. Idzerda; Elke Arenholz and Yves U. Idzerda were co-authors of the article, 'Elemental moment variation of bcc Fe xMn 1-x on MgO(001)' submitted to the journal 'Physical reviews B' which is contained within this thesis.Magnetic memory storage industry is always searching for materials that can store, read, and write data ever so faster, with lower power, with accuracy and on denser packaging. The material research was spurred with discovery and successful implementation of Giant Magnetoresistance phenomena into critical components of devices. GMR devices essentially were multilayered thin films of a set of magnetically ordered metals. Fe-Mn thin films were used to create one of its moment pinning layers. Fcc Fe-Mn thin films were studied enthusiastically for their AFM properties but very little was known about the rare bcc structured single crystals. Bcc Fe-Mn was found to be ferromagnetic in parts of phase diagram of Fe-Mn. The magnetic moment of alloys usually follows a regular linear trend based upon electronic configuration of constituent elements, known as Slater-Pauling curve. While most alloys follow the trend, bcc Fe-Mn binary alloys show a dramatic collapse in the bulk magnetic moment, as concentration of Mn is varied. In this work, we successfully fabricate bcc single crystal thin film of Fe-Mn on MgO(001) substrate by Molecular Beam Epitaxy method. We confirm using Reflection High Energy Electron Diffraction that, the bcc phase of Fe-Mn thin film is achieved, albeit being a forced structure, stable up to 35% of Mn concentration. X-ray absorption spectra of individual elements were used to confirm the compositions of Fe-Mn films and x-ray magnetic circular dichroism was used to track the elemental magnetic moment as the composition was varied. We found that the magnetic moment of Fe drops faster than expected and Mn has very small identical moment in all compositions. We also successfully created a compositionally graded Fe-Mn sample in MBE and spatially mapped its Fe moment by around the critical composition. The mechanism for collapse of magnetic moment over a spread of composition of Mn is a very complex problem yet we provide our experimental findings of unprecedented resolution to confirm that bcc Fe-Mn can be structurally stable up to 35% Mn and that the magnetic moment of the alloy starts with onset of Fe moment at 14% Mn and is complete by 17% Mn.Item Nonlinear excitations in the two-dimensional classical Heisenberg magnet(Montana State University - Bozeman, College of Letters & Science, 1993) Grigereit, Todd Edward