Lecture Hans M. Christen
|16 June 2010||FWN-Building 5114.0004, Nijenborgh 4, 9747 AG, Groningen|
|Speaker:||Dr. Hans M. Christen|
|Date:||Wed Jun 16, 2010|
|Telephone:||+31 50 363 4565|
A surprisingly rich variety of physical properties is found in the perovskite family of metal-oxides, which includes metals, insulators, superconductors, ferromagnets, ferroelectrics, and nonlinear optical media. In many cases, their properties result from electronic correlations, and recent work by a number of teams across the world has shown that the resulting behaviors are strongly influenced by effects at interfaces. Such interfaces – atomically abrupt junctions between dissimilar perovskites – can be formed for example by pulsed-laser deposition, and interfaces can be “stacked” to create new macroscopic properties in superlattices.
In this talk, I will show how new magnetic properties emerge at the interface between LaMnO3 (which is antiferromagnetic in its bulk form) and nonmagnetic insulating perovskites, such as SrTiO3 and LaAlO3. By tailoring the periodicity of the superlattice, we can drastically change its magnetization while the average composition remains the same. We use a combination of techniques to probe the origins of these interfacial behaviors: By varying the periodicity in three-component superlattices (A/B/C/A/B/C etc.), we can identify the length scales and the relative strengths of the individual interfacial enhancements. A more direct observation of the interfacial magnetism is obtained via polarized neutron reflectometry, which reveals the magnetization profile across a film with a spatial resolution better than 0.5 nm in the direction perpendicular to the interfaces. Z-contrast scanning transmission electron microscopy (Z-STEM) and energy electron loss spectroscopy (EELS) imaging allows us to probe the local Mn valence state. Our results point to a previously unobserved structural origin to interfacial enhancements of magnetization that is distinctively different from strain and can only be achieved near interfaces.
He presented work is a collaboration with H.S. Kim, M.D. Biegalski, H.N. Lee, M. Varela, J. Gazquez, V. Lauter, H. Ambaye, and S.E. Nagler (all ORNL). Research sponsored by the Division of Materials Science and Engineering and the Division of Scientific User Facilities, US Department of Energy.
|Last modified:||22 October 2012 2.30 p.m.|