Magnetic spectroscopy and microscopy of functional materials

Heusler intermetallics Mn$_{2}Y$Ga and $X_{2}$MnGa ($X,Y$=Fe, Co, Ni) undergo tetragonal magnetostructural transitions that can result in half metallicity, magnetic shape memory, or the magnetocaloric effect. Understanding the magnetism and magnetic behavior in functional materials is often the most direct route to being able to optimize current materials and design future ones.rnrnSynchrotron soft x-ray magnetic spectromicroscopy techniques are well suited to explore the the competing effects from the magnetization and the lattice parameters in these materials as they provide detailed element-, valence-, and site-specific information on the coupling of crystallographic ordering and electronic structure as well as external parameters like temperature and pressure on the bonding and exchange.rnrnFundamental work preparing the model systems of spintronic, multiferroic, and energy-related compositions is presented for context. The methodology of synchrotron spectroscopy is presented and applied to not only magnetic characterization but also of developing a systematic screening method for future examples of materials exhibiting any of the above effects. rnrnChapters include an introduction to the concepts and materials under consideration (Chapter 1); an overview of sample preparation techniques and results, and the kinds of characterization methods employed (Chapter 2); spectro- and microscopic explorations of $X_2$MnGa/Ge (Chapter 3); spectroscopic investigations of the composition series Mn$_{2}Y$Ga to the logical Mn$_3$Ga endpoint (Chapter 4); and a summary and overview of upcoming work (Chapter 5). Appendices include the results of a “Think Tank” for the Graduate School of Excellence MAINZ (Appendix A) and details of an imaging project now in progress on magnetic reversal and domain wall observation in the classical Heusler material Co$_2$FeSi (Appendix B).

Mn$_{2}Y$Ga and $X_{2}$MnGa ($X,Y$=Fe, Co, Ni) mit Heuslerstruktur sind Halbleiter und Formgedächtnislegierungen. Um das Verhalten zu verstehen, muss man das magnetische Materialverhalten charakteresieren. Weiche Röntgenstrahlung von einer Synchrotron-Strahlungsquelle sowie die Advanced Light Source in Berkeley sind ideal für diese Untersuchungen geeignet. rnrnInhalt: Kapitel 1 ist ein Übersicht über die verwendeten Methoden und Materialien. Kapitel 2 gibt eine Einleitung zu Sputtering und Charakterisierungsverfahren. Kapitel 3 präsentiert Ergebnisse von $X_2$MnGa/Ge. In Kapitel 4 werden Ergebnisse zu Mn$_{2}Y$Ga präsentiert. In Kapitel 5 werden die Ergebnisse zusammengefasst. Appendix A beschreibt das ''Think Tank"-Projekt. Appendix B beschreibt einen neuen Absatz für die Beobachtung der magnetischen Domänenwand in Co$_2$FeSi.