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Department Library

2020

Nicolas Ducharme (Senior Thesis, April 2020, Advisor: Benjamin Frandsen )

Abstract

Dilute magnetic semiconductors (DMSs) are of interest to physicists and materials scientists due to their potential applications in spintronics and quantum computing. The research I will present is not directly aimed at spintronic or quantum computing applications. Rather, it is aimed at understanding the detailed atomic and magnetic structure of DMSs, which will enable a more fundamental understanding of their properties and facilitate future applications. Two DMSs, Li(Zn,Mn)As and (Ba,K)(Zn,Mn)2As2 were investigated experimentally, with the data analyzed via pair distribution function (PDF) analysis of x-ray and neutron scattering data. Li(Zn,Mn)As was found to lack local structural deviations and possesses only weak magnetic order, while (Ba,K)(Zn,Mn)2As2 was found to have significant local structural deviations and possess more robust magnetic order. These findings suggest that useful magnetic correlations may be connected to local structural deviations. Keywords: dilute magnetic semiconductor; local structure; magnetic correlations; short-range magnetic order; spintronics

Jake Hughes (Capstone, August 2020, Advisor: Benjamin Frandsen )

Abstract

The properties of materials are strongly dependent on the crystal structure of the material. The atomic pair distribution function (PDF) method is a powerful method for investigating the structure of materials on length scales of several unit cells. Determining the positions of atoms within the unit cell is crucial to gaining an understanding of the overall structure of the material, but traditional methods of refining a model against experimental PDF data to determine atomic positions can be time intensive and possibly unreliable. We have taken a new approach to traditional PDF modeling using symmetry mode analysis enabled by the ISODISTORT program. Instead of using conventional Cartesian coordinates as fitting parameters, we fit symmetry mode amplitudes to try to reproduce simulated data and determine which distortion modes are active in each structure. This approach may lead to more effective modeling of experimental data and more accurate determinations of crystal structure.