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SPINTRONICS(Nano Magnetism) • UC-Berkeley, Physics • Jusang Park PhD.
EDUCATIONPh. D. CONDENSED PHYSICS2007HANYANG UNIVERSITY, Seoul, Korea TECHNICAL EXPERTISEM. S. CONDENSED PHYSICS1997 Instrument/ System development:HONGIK UNIVERSITY, Seoul, Korea Development and construction of several vacuumB. S. PHYSICS processing and measurement systems: UHV- STM, SMOKE,1995 Electron-Beam Evaporation System.ANDONG NATIONAL UNIVERSITY, Andong, Korea Thin film growth: Thermal E-beam evaporation systems. ThermalRESEARCH EXPERIENCE Evaporation systems.Department of Physics, University of California at Berkeley Structural and Surface analysis :2009-present Low Energy Electron Diffraction (LEED), Atomic ForcePostdoctoral Associate, Advisor: Prof. Z. Q. Qiu Microscopy (AFM) , Scan Tunneling Microscopy (STM),I investigated nano-magnetism in magnetic thin films. Photo Emission Electron Microscopy (PEEM), ScanningDeveloped and built various vacuum processing and magnetic Electron Microscope (SEM).measurement systemsCollaborated with various research partners (LBNL, UC DAVIS, and the Magnetic Characterization:other UC Berkeley department) X-ray Magnetic Circular Dichroism (XMCD), X-ray Magnetic Linear Dichroism (XMLD), Spin-Polarized Low EnergyQuantum Photonic Science Research Center in Hanyang University Electron Microscopy (SPLEEM), Superconducting Quantum2006-2009 Interference Device (SQUID).Additional Doctoral Research:To further dissertation work, studied the fabrication of metallic thinfilms and numerous Mn oxides, including magnetic alloy.Korea Research Institute of Standards and Science2003-2006Additional Doctoral Research:Investigated exchange bias effect of mono-layers of Fe on Pt (110) byusing In-situ SMOKE, XMCD, STM etc.Developed and built UHV-STM and SMOKE measurement systems.
Why nanomagnetism? What nano scale? • Spintronics? • Combination of “charge” and “spin” in nanostructures 2D 1D 0D Charge Scalar + + Spin Vector FM/AFM interface Nano-structureScalar + vector = more degree offreedomA great example: GMR MA better understanding of “spin” atnano-scale is needed. H Bubble domain vortex Exchange bias
How to prepare the sample double wedge sample with MBE growthFerromagnetic thin film (Co, Ni, FCT Fe) Curie Temperature AnisotropyAntiferromagnetic thin film (FeMn) Neel Temperature Magnetic disorderNonmagnetic thin film (Cu, FCC Fe) Interlayer coupling strength • NiO/Fe(15ML)/Ag(001) & CoO/Fe(15ML)/Ag(001) MBE grown sample • Focused Iron Beam (FIB) 30keV Ga iron sputtering, ~10nm focus size • PEEM imaging XMCD for Fe; XMLD for NiO & CoO m
PEEM (photoemission electron microscopy) :Element specific Image LCP light Dm=+1 RCP light Dm=-1 Domain image E E LCP Right RCP Left L3 L22p3/2(L3) ~ ~ 2p3/2(L3) ~ ~ 780 800 820 photo energy(eV) 840 L3 L2 Photon energy (eV) Before X-rays After
An example: interlayer coupling in Co/NiO/Fe trilayer Element-specific measurement Co NiO Fe Co NiO Fe NiO XMLD image provides the key information to understand the anomalous Co-Fe interlayer coupling.However, XMLD is limited to single crystalline oxides, e.g. NiO, CoO.
Magnetic Vortex in Antiferromagnet • Spin Excitations • Quantum Phase Transition Skyrmion of 2D Antiferromagnet T. Senthil et. al., Science 303, 1490 (2004).Imprinting Magnetic Vortex in FM/AFM BilayersIndirect evidence- Characteristic asymmetric hysteresis loops- Vortex of the induced FM signal from the AF layer Ir20Mn80/Ni80Fe20 XMCD Fe Mn G. Salazar-Alvarez, et. al., Appl. Phys. Lett. 95, 012510 (2009).
Two types of AFM vortex Fe XMCD Co XMLDOur proposal: Competition tuned by interlayer coupling vortex dNiO=0.6 nm; SFe // SCoO orsingle domain FM coupling D=4 mm AFM or coupling dCoO=3.5 nm; SFe ┴ SCoOTuning coupling strength allows us to choose magnetic ground state.
Our methodology Quantum well state formed in thin film can be employed to retrieve band structure.At fixed film thickness d Oscillatory Coupling E Magneto-Optic Effect GMR Thickness stability Magnetic Anisotropy DOS d At fixed energy E The periodicity of the oscillation in DOS with film thickness is determined by the momentum of valence electrons (kin,). DOS d
Spintronics Revolution via Spin Engineering Magnetic Recording MRAM Spin Transistor Spin-Valve Head Pinned layer Bit line Current “1” “0” Memory cell Word line with binary information Free layer • Density of DRAM Tb/in2 before 2010 ! • Speed of SRAM IBM 256 Mb(’04) • Non-volatility Samsung 64Kb(’03) • Large Magnetocurrent(3500%) • Low power • High Speed( 〉10GHz) • Small collector current(~ 10 nA) Biosensor Spin LED Quantum Computer Wang, INTERMAG(’03) Electron Spins in Quantum dots as Qubits Ohno, Nature(’99)
Analysis of Cu(100nm)/Ru(3nm)/TaN(3nm) /SiO(1um)/Si SEM No 3. No 8. No 9. No10. PEEM spectrum of elements Distribution of Cu Distribution of RuGeometry Ru Cu O No 10. No 9.450 480 925 950 490 560 630
Spin-Organic Light Emitting Diode Cathode InterfaceOLED • Metal Diffusion light emission • Introduction of Impurities • Barrier - poor e- injection V Ferromagnetic metal cathodes Spin Coated Polymer (Ir(ppy)3) Spin coating processITO Glass substrate - Fe, Al anodeAnode (ITO) Interface Rate: 5 A/s• Indium, Oxygen Diffusion• Barrier – poor h+ injection Base pressure: 10-7 Torr• Variations in morphology - Organic layer• Variations in work function Spin Coating 4000RPM E-beam evaporation system
Two sepereated UHV STM systems Variable temperature SMOKE/LEED system Fe-Pt surface alloy: STMPt(110) surface: 1KeV Ar-ion sputtering + annealing at 1000 KFe evaporation: e-beam bombarded Fe plate (4N) STM head and principle Piezo tube 200nm Tip cartridge Sample