Layered ruthenates in the Ruddlesden-Popper series (Sr,Ca) n+1RunO3n+1 exhibit exceptionally rich ground state properties, such as unconventional spin-triplet superconductivity, orbital ordering, and metamagnetic quantum criticality. These unusually rich ground states headline the complex interplay between the charge, spin, lattice and orbital degrees of freedom in ruthenates, and provide fantastic opportunities to study novel quantum phenomena tuned by non-thermal parameters like chemical doping, pressure, and magnetic field We focus on two particular layered ruthenates, each with rich ground state properties. First, Sr4Ru3O10 exhibits an itinerant ferromagnetic ground state, but moderate in-plane magnetic fields induce a metamagnetic transition. The presence of both ferromagnetism and metamagnetism in this material is puzzling and has been the subject of extensive study. The other material studied here, Ca3Ru2O 7 orders antiferromagnetically at 56 K and exhibits a metal-insulator transition at 48 K. With the application of magnetic field this material shows spin-flop transition causing giant magnetoresistance. Neutron scattering studies have revealed a rich magnetic phase diagram with four different magnetic phases In this dissertation we aim to elucidate the orbital dependence of the magnetism in Sr4Ru3O10 and the nature of the complex coupling between spin and charge in Ca3Ru2O 7. In order to achieve these aims we developed a directional angle-resolved magnetotransport technique, as magnetoresistivity anisotropy is a powerful analysis tool. With this technique we revealed the metamagnetism in Sr 4Ru3O10 to be orbital selective, i.e. the metamagnetism and ferromagnetism arise from different orbitals. In Ca3Ru 2O7 we studied the nature of the effects of ferromagnetic and antiferromagnetic coupling on c-axis transport throughout the different magnetic phases in this material by analyzing the magnetoresistivity anisotropy, and have observed a complex interplay between the charge and spin degrees of freedom that were dependent on both temperature and magnetic field By utilizing a relatively simple technique we have probed the nature of the magnetism in two materials. In addition to revealing important physics in these two materials, our results suggest possible avenues of investigation in other ruthenates and strongly correlated systems using the developed technique / acase@tulane.edu
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_24104 |
| Date | January 2010 |
| Contributors | Fobes, David M (Author), Kim, Daeho (Thesis advisor) |
| Publisher | Tulane University |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Rights | Access requires a license to the Dissertations and Theses (ProQuest) database., Copyright is in accordance with U.S. Copyright law |
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