SPINTRONICS(Nano Magnetism)

• UC-Berkeley, Physics

• Jusang Park PhD.

EDUCATION

Ph. D. CONDENSED PHYSICS 2007HANYANG UNIVERSITY, Seoul, Korea M. S. CONDENSED PHYSICS 1997HONGIK UNIVERSITY, Seoul, KoreaB. S. PHYSICS 1995ANDONG NATIONAL UNIVERSITY, Andong, Korea

RESEARCH EXPERIENCE

Department of Physics, University of California at Berkeley 2009-presentPostdoctoral Associate, Advisor: Prof. Z. Q. QiuI investigated nano-magnetism in magnetic thin films.Developed and built various vacuum processing and magnetic measurement systemsCollaborated with various research partners (LBNL, UC DAVIS, and the other UC Berkeley department)

Quantum Photonic Science Research Center in Hanyang University 2006-2009Additional Doctoral Research: To further dissertation work, studied the fabrication of metallic thin films and numerous Mn oxides, including magnetic alloy.Korea Research Institute of Standards and Science 2003-2006 Additional Doctoral Research: Investigated exchange bias effect of mono-layers of Fe on Pt (110) by using In-situ SMOKE, XMCD, STM etc.Developed and built UHV-STM and SMOKE measurement systems.

TECHNICAL EXPERTISE

Instrument/ System development: Development and construction of several vacuum processing and measurement systems: UHV- STM, SMOKE, Electron-Beam Evaporation System.

Thin film growth: Thermal E-beam evaporation systems. Thermal Evaporation systems.

Structural and Surface analysis : Low Energy Electron Diffraction (LEED), Atomic Force Microscopy (AFM) , Scan Tunneling Microscopy (STM), Photo Emission Electron Microscopy (PEEM), Scanning Electron Microscope (SEM).

Magnetic Characterization: X-ray Magnetic Circular Dichroism (XMCD), X-ray Magnetic Linear Dichroism (XMLD), Spin-Polarized Low Energy Electron Microscopy (SPLEEM), Superconducting Quantum Interference Device (SQUID).

Why nanomagnetism?

Charge+ Spin

Scalar + Vector

Scalar + vector = more degree of freedomA great example: GMRA better understanding of “spin” at nano-scale is needed.

• Spintronics?

• Combination of “charge” and “spin” in nanostructures

1D

M

H

2D

FM/AFM interface Nano-structure

Bubble domainExchange bias

vortex

0D

What nano scale?

m

How to prepare the sampledouble wedge sample with MBE growth

Curie Temperature

Interlayer coupling strength

Ferromagnetic thin film (Co, Ni, FCT Fe)

Nonmagnetic thin film (Cu, FCC Fe)

AnisotropyAntiferromagnetic thin film (FeMn)

Neel Temperature

Magnetic disorder

• 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 imagingXMCD for Fe; XMLD for NiO & CoO

PEEM (photoemission electron microscopy) :Element specific Image

780 800 820 840

Right

Left

photo energy(eV)

Photon energy (eV)

LCPRCP

2p3/2(L3)

E

~~

E

~~

LCP light Dm=+1 RCP light Dm=-1

2p3/2(L3)

L3 L2

L3 L2

Domain image

Before

After

X-rays

An example: interlayer coupling in Co/NiO/Fe trilayer

NiO XMLD image provides the key information to understandthe anomalous Co-Fe interlayer coupling.

Fe

NiO

Co

Element-specific measurement

Fe

NiO

Co

However, XMLD is limited to single crystalline oxides, e.g. NiO, CoO.

T. Senthil et. al., Science 303, 1490 (2004).

• Spin Excitations• Quantum Phase Transition

Imprinting Magnetic Vortex in FM/AFM Bilayers

Indirect evidence

- Characteristic asymmetric hysteresis loops

- Vortex of the induced FM signal from the AF layer

Skyrmion of 2D Antiferromagnet

Ir20Mn80/Ni80Fe20

Fe MnXMCD

G. Salazar-Alvarez, et. al., Appl. Phys. Lett. 95, 012510 (2009).

Magnetic Vortex in Antiferromagnet

Our proposal: Competition tuned by interlayer coupling

vortex

single domain FMcoupling

AFMcoupling

or

or

Tuning coupling strength allows us to choose magnetic ground state.

D=4 mm

dNiO=0.6 nm; SFe // SCoO

Fe XMCD Co XMLD

dCoO=3.5 nm; SFe ┴ SCoO

Two types of AFM vortex

Our methodology

dDOS

E

DO

S

d

The periodicity of the oscillation in DOSwith film thickness is determined by themomentum of valence electrons (kin,).

Quantum well state formed in thin film can be employed toretrieve band structure.

At fixed film thickness d

At fixed energy E

GMR

Magneto-Optic Effect

Oscillatory Coupling

Magnetic Anisotropy

Thickness stability

0 2 4 6 8 10 12

6

8

10

12

14

Co Thickness (ML)

En

erg

y (

eV

)

0 2 4 6 8 10 12

6

8

10

12

14

En

erg

y (

eV

)

Co Thickness (ML)

Biosensor

Wang, INTERMAG(’03)

Spintronics Revolution via Spin EngineeringMRAM

• Density of DRAM• Speed of SRAM• Non-volatility• Low power

Bit line

“1” “0”

Word line

Memory cell with binary information

IBM 256 Mb(’04)Samsung 64Kb(’03)

Cu

rre

nt

Pinned layer

Free layer

Magnetic RecordingSpin-Valve Head

Tb/in2 before 2010 !

Spin Transistor

• Large Magnetocurrent(3500%)• High Speed( 〉10GHz)• Small collector current(~ 10 nA)

Quantum Computer

Electron Spins in Quantum dots as Qubits

Spin LED

Ohno, Nature(’99)

Collaborators

No 3.

No 8.No 9.No10.

SEM

Analysis of Cu(100nm)/Ru(3nm)/TaN(3nm)/SiO(1um)/Si

450 480 925 950 490 560 630

Ru

Cu

O

PEEM spectrum of elements

No 10.

Distribution of Cu

No 9.

Distribution of RuGeometry

Spin-Organic Light Emitting Diode

- Fe, Al anode

Rate: 5 A/s

Base pressure: 10-7 Torr

- Organic layer

Spin Coating 4000RPM

V

Glass substrate

Spin Coated Polymer (Ir(ppy)3)

Ferromagnetic metal cathodes

OLED

ITO

Cathode Interface• Metal Diffusion• Introduction of Impurities• Barrier - poor e- injection

Anode (ITO) Interface• Indium, Oxygen Diffusion• Barrier – poor h+ injection • Variations in morphology• Variations in work function

light emission

Spin coating process

E-beam evaporation system

Two sepereated UHV STM systems

Pt(110) surface: 1KeV Ar-ion sputtering+ annealing at 1000 K

Fe evaporation: e-beam bombarded Fe plate (4N)

Variable temperatureSMOKE/LEED system

Tip cartridge

Piezotube

Sample

200nm

STM head and principle

Fe-Pt surface alloy: STM