Speaker: Xiaoqian (Michelle) Chen, University of Illinois at Urbana-Champaign
Date & Time: July 28, 2014 11:00 - 12:00
Location: UBC, AMPEL 311
Local Contact: Andrea Damascelli
Intended Audience: Graduate
Spatial confinement effects can be a useful tool to disentangle the complexity of strongly correlated systems. In case of manganites, factors like super exchange, double exchange, Hund’s rule coupling, or electron kinetic energy can compete for its determination of a ground state. When the spatial dimension of a material is reduced, its ground state can be altered by the difference in correlation lengths of these underlying competing orders. This raises the question of how boundary effects influence the phase of such a system, and whether spatial confinement can influence the properties of a nanoscale object. To answer these questions, we fabricated arrays of nanowires from the CMR material La1-xSrxMnO3 (LSMO) using e-beam lithography. In bulk or thin film, LSMO undergoes a para- to ferromagnetic phase transition at the Curie temperature (Tc). Our magnetization measurements performed on these wires suggest the existence of an additional magnetic ordering at a temperature much lower than Tc. Around this temperature, domain switching was also observed in transport measurements. To understand these observations, we performed resonant soft x-ray scattering studies at the Mn L edge. We observed a series of grating reflections and superlattice reflections whose magnetic signals are temperature dependent. These observations indicate the emergence of a nontrivial magnetic ordering inside the wires at different length scales as the temperature is lowered. To determine the exact magnetic structure, we are in the process of modeling the scattering using a numerical method combining least-square fitting and algorithmic phase retrieval. This analysis will reveal the real-space magnetization density distribution inside the nanowires with nanometer resolution.