Time-resolved scanning transmission x-ray microscopy studies of spin current induced manipulation of magnetization in nanostructures
Final Report Abstract
By using the nanometer scale resolution of Scanning Transmission X-ray microscopy (STXM) measurements combined with time resolution given by the ALS ring, we were able to investigate current-induced magnetization switching (CIMS) dynamics driven by polarized current pulses in perpendicularly magnetized (PMA) samples. We observed that the fast switching is highly nonuniform for 300x100 nm2 ellipses. The STXM observations are well reproduced using micromagnetic calculations which allow discussing the details of the nucleation/propagation process occurring during the magnetization switching. Finally, a high domain wall speed of around 100 m/s with a current density of ~5x107 A/cm2 is measured and reproduced within the simulations. Next it would be interesting to study the impact of those nonuniform magnetization on switching speed and thermal stability which are two important features for future spin torque MRAM applications. STXM was also employed to unravel the grain size and orientation of pentacene based fieldeffect transistors on the nanometer length scale. The transistor devices were built on a SiNx membrane coated with SiO2. The pentacene growth conditions were varied by using different self assembled monolayers (SAMs) on top of the SiO2. It was shown that the STXM technique allows determining the molecular in-plane angle with an accuracy of ±4° and that it could be combined with AFM measurements. The grain size increases with increasing alkyl chain length of the SAM, 1.4 μm for Octatrichlorsilane to 2.8 μm for Octadecyltrichlorsilane. In the same sequence, the ratio of grain boundaries to the total surface area decreases and the charge carrier mobility increases. The developed method to determine the molecular orientation is a very important step to improve the performance of organic electronic devices and to make them more attractive for future applications. The success of the organic field effect transistor project was not expected. In fact, many research groups at Stanford University were interested in investigating their samples with the developed technique which led to several joint research projects.
Publications
- Electronic and magnetic properties of Ni nanoparticles embedded in various organic semiconductor matrices, J. Phys. Chem. B., 2009, 113, 4565-4570
B. Bräuer, Y. Vaynzof, W. Zhao, A. Kahn, W. Li, D. R. T. Zahn, C. J. Fernández, C. Sangregorio, G. Salvan
- Fraunhofer Institute Dresden in Dresden, Germany, Scanning Transmission X-ray Microscopy Imaging of Magnetic Nanostructures and Organic Semiconductor Devices, 12/14/09
B. Bräuer, Y. Acremann, Z. Bao, J. Stöhr
- Karlsruhe Institute of Technology in Karlsruhe, Germany, X-ray Microscopy Imaging of Magnetic Nanostructures and Organic Semiconductor Devices, 12/18/09
B. Bräuer, Y. Acremann, Z. Bao, J. Stöhr
- Magneto-optical Kerr effect spectroscopy – a sensitive tool for investigating the molecular orientation in organic semiconductor films, J. Phys. Chem. B, 2009, 113, 14957-14961
B. Bräuer, M. Fronk, D. Lehmann, D. R. T. Zahn, G. Salvan
- University Würzburg in Würzburg, Germany, X-ray Microscopy Imaging of Magnetic Nanostructures and Organic Semiconductor Devices, 12/17/09
B. Bräuer, Y. Acremann, Z. Bao, J. Stöhr
- American Physical Society Conference in Portland, Oregon/USA, Scanning transmission X-ray microscopy imaging of the grain orientation in pentacene field-effect transistors; Time Resolved X-ray Imaging of Magnetic Dynamics in Perpendicularly Magnetized Nanopillars, 03/15 to 03/19/10
B. Bräuer, Y. Acremann, A. Virkar, S. Mannsfeld, D. Bernstein, R. Kukreja, Z. Bao; D. Bernstein, B. Bräuer, R. Kukreja, Y. Acremann
- Hamburg University in Hamburg, Germany, X-ray Microscopy Imaging of Magnetic Nanostructures and Organic Semiconductor Devices, 01/21//10
B. Bräuer, Y. Acremann, Z. Bao, J. Stöhr
- Hitachi Global Storage Technologies in San Jose, California, USA, X-ray Imaging of Magnetization Dynamic, 09/08/10
B. Bräuer
- Karlsruhe University in Karlsruhe, Germany, X-ray Microscopy Imaging of Magnetic Nanostructures and Organic Semiconductor Devices, 04/30/10
B. Bräuer, Y. Acremann, Z. Bao, J. Stöhr
- KLA-Tencor in Beaverton, Oregon, USA, Scanning Transmission X-ray Microscopy: Imaging of Magnetization Dynamics, 08/24/10
B. Bräuer
- Lawrence Berkeley Laboratory (LBL) in Berkeley, California, USA, X-ray Microscopy Imaging of magnetic Nanostructures and Organic Semiconductor Devices, 06/09/10
B. Bräuer
- Material Research Society Conference in San Francisco, California/USA, Scanning transmission X- ray microscopy imaging of the grain orientation in pentacene field-effect transistors, 04/05 to 04/09/10
B. Bräuer, Y. Acremann, A. Virkar, S. Mannsfeld, D. Bernstein, R. Kukreja, Z. Bao
- Max Planck Institute Stuttgart in Stuttgart, Germany, X-ray Microscopy Imaging of Magnetic Nanostructures and Organic Semiconductor Devices, 01/18/10
B. Bräuer, Y. Acremann, Z. Bao, J. Stöhr
- Stanford University in Stanford, California, USA, X-ray Microscopy Imaging of Magnetic Nanostructures and Organic Semiconductor Devices, 05/13/10
B. Bräuer, Y. Acremann, Z. Bao, J. Stöhr
- X-ray microscopy imaging of the grain orientation in a pentacene fieldeffect transistor, Chem. Mater, 2010, 22, 3693-3697
B. Bräuer, A. Virkar, S. C. B. Mannsfeld, D. P. Bernstein, R. Kukreja, K. W. Chou, T. Tyliszczak, Z. Bao, Y. Acremann
- Xerox - Palo Alto Research Center (PARC) in Palo Alto, California, USA, X-ray Microscopy Imaging of Magnetic Nanostructures and Organic Semiconductor Devices, 05/21/10
B. Bräuer
