2006 - Pres. Center for Nanoscale Systems at Cornell University [Robert A. Buhrman & Dan C. Ralph]
Understand the reversal and dynamic behavior of spin transfer torque, and explore possible application in non-volatile magnetic memory. More details coming.
2002 - 2006 Physics department at University of California, San Diego [ Ivan K. Schuller ]
Study in-depth the mechanism of FeF2 exchange bias bilayers and nanostructures. Namely, how one can probe the exchange bias mechanism by means of nanostucturing, and how one can engineer the reversal behavior by exchange bias. Many unexpected behaviors have been found, which elucidates important aspects of the exchange bias phenomena, esp. the asymmetrical reversal mechanism, FM/AF domain size relevance.
EB Nanostructures:
- Demonstrated AF domain size relevance compared with FM dot size, and how exchange bias could be influenced by magnetic vortex state.
- Set up a low temperature high magnetic field (up to 7T) magneto-optical Kerr effect (MOKE) system, and designed another low temperature diffraction MOKE system.
- Modeling by micromagnetic and Monte-Carlo simulations.
Samples fabrication using e-beam evaporation, e-beam lithography, ion beam etching.- Characterization by AFM/MFM, x-ray diffraction, magneto-optical Kerr effect, SQUID.
Exchange bias thin films
- Demonstrated AF domain size relevance compared with FM domain wall width.
- Demonstrated for the first time the existence of FM exchange spring in FM/AF bilayer.
- Systematically studied origins of asymmetric reversal.
- Discovered tunable temperature hysteresis in thermally induced spontaneous reversal and its peculiar dynamic behavior.
- Wide range of collaborations with many groups: XMCD, polarized neutron reflectivity, coherent X-ray scattering, XPS, vector magnetometry, low temperature MFM/STM, TEM, STEM, etc.
Developing reflection X-ray holography (Collaboration with S. Sinha and S. Roy)
- Experimental design, simulation, and data processing.
- Nanofabrication by e-beam lithography, RIE, magnetron sputtering, e-beam evaporation.
Spin Polarized Tunneling
- Demonstrated bias-dependent oscillations in magneto-resistance in MgO tunnel junctions.
- Simulated this behaviour to show how this oscillation is influenced by junction parameters.
2000 - 2002 Yale University [Robert Grober]
- Set up a low temperature photoluminescence (PL) to study PL spectroscopy of GaAs/AlGaAs quantum well. Studied the temperature dependence of the integral intensity of PL spectrum.
- Proposed and designed the high-impedance ground plane substrate. It enhances single molecule PL signal by a factor of 8 for low pump intensity or a factor of 2 for high pump intensity. This result greatly improves the signal-noise ratio and the imaging quality of single molecule PL spectroscopy.
1998 - 2000 Peking University [Dapeng Yu]
Fabrication of silicon nanowires for transport measurement. Optimized in situ growth of silicon nanowire on STM tips by CVD. Characterization by by SEM, and TEM.