SrTiO 3 [010]

1. SrTiO3 [010] Domain 2 Domain 1 SrTiO3 [100] { 1/2 1/2 1/2 } reflections Domain 2 Domain 1 { 3/2 3/2 3/2 } reflections Domain 1 Domain 2 Spin-Polarization Dependence of Non-Resonant Magnetic X-ray Diffraction in Multi-Domain BiFeO3Paul G. Evans (University of Wisconsin-Madison),DMR 0705370 Magnetic multiferroics can simultaneously have intriguing electrical and magnetic properties – and thus present the opportunity to allow these properties to interact. Bismuth ferrite (BiFeO3) is especially interesting because it is both ferroelectric and antiferromagnetic at room temperature. We are using synchrotron x-ray magnetic diffraction to probe the antiferromagnetism of BiFeO3 thin films and to understand its evolution in applied electric fields. Magnetic x-ray diffraction is a powerful probe for antiferromagnets because the intensity of the magnetic reflections depends on direction of the spins in the antiferromagnetic lattice relative to the crystallographic basis vectors and because x-rays can be focused to small spots to allow multiferroic capacitors with micron-scale electrodes to be studied. The polar plots of predicted cross sections at right are made for magnetic reflections appearing the pseudo-cubic {1/2 1/2 1/2} and {3/2 3/2 3/2} families. The intensities of the reflections from the two structural domains of a multi-domain (001)-oriented BiFeO3 thin film are shown. The difference in the cross sections between domains allows us to compare observed intensities in BiFeO3 thin films and to determine the direction of the magnetic moment. Interpreting the magnetic diffraction from multi-domain samples allows us to study the response of the antiferromagnetism in (001)-oriented BiFeO3 films to applied electric fields.

2. Spin-Polarization Dependence of Non-Resonant Magnetic X-ray Diffraction in Multi-Domain BiFeO3Paul G. Evans (University of Wisconsin-Madison),DMR 0705370 Undergraduates are active participants in research conducted both at the University of Wisconsin-Madison and at National facilities. Roberto Cruz (top photo), a mechanical engineering undergraduate from University of Puerto Rico, Mayaguez worked with the Evans group in Summer 2008 through the University of Wisconsin’s SURE REU program. Roberto assembled and calibrated an x-ray diffractometer based on a rotating anode x-ray generator. Roberto’s work will allow further structural studies of BiFeO3 and other related multiferroic materials. Roberto plans to study materials science in graduate school. University of Wisconsin undergraduate Adam Jandl (lower photo) has worked with graduate student Rebecca Sichel in magnetic scattering experiments using x-ray microdiffraction facilities at the Advanced Photon Source of Argonne National Laboratory. Adam also plans to pursue a PhD in materials science.