Correlating Interfacial Structure and Magnetism in Thin-Film Oxide Heterostructures Using Transmission Electron Microscopy and Polarized Neutron Reflectometry

Download or read book Correlating Interfacial Structure and Magnetism in Thin-Film Oxide Heterostructures Using Transmission Electron Microscopy and Polarized Neutron Reflectometry written by Steven Richard Spurgeon and published by . This book was released on 2014 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: Oxide thin-films have attracted considerable attention for a new generation of spintronics devices, where both electron charge and spin are used to transport information. However, a poor understanding of the local features that mediate magnetization and coupling in these materials has greatly limited their deployment into new information and communication technologies. This thesis describes direct, local measurements of structure-property relationships in ferrous thin-films and La1-xSrxMnO3 (LSMO) / Pb(ZrxTi1-x)O3 (PZT) thin-film heterostructures using spatially-resolved characterization techniques. In the first part of this thesis we explore the properties of ferrous spintronic thin-films. These films serve as a model system to establish a suite of interfacial characterization techniques for subsequent studies. We then study the static behavior of LSMO / PZT devices with polarization set by the underlying substrate. Using transmission electron microscopy and geometric phase analysis we reveal the presence of significant local strain gradients in these films for the first time. Electron energy loss spectroscopy mapping of the LSMO / PZT interface reveals Mn valence changes induced by charge-transfer screening. Bulk magnetometry and polarized neutron reflectometry indicate that these chemical and strain changes are associated with a graded magnetization across the LSMO layer. Density functional theory calculations are presented, which show that strain and charge-transfer screening act locally to suppress magnetization in the LSMO by changing the Mn orbital polarization. In the second half of this thesis, we explore asymmetric screening effects on magnetization LSMO / PZT composites. We find that the local ferroelectric polarization can vary widely and that this may be responsible for reduced charge-transfer effects, as well as magnetic phase gradients at interfaces. From this information and electron energy loss spectroscopy, we construct a map of the magnetic phases at the interface. Collectively these results show that we must move toward high-resolution local probes of structure and magnetism to achieve deterministic control of functional thin-film oxides.