스핀토크 Summer School2008. 7. 2 - 4

수송특성 측정방법수송특성 측정방법

서 강 대 학 교서 강 대 학 교

극한양자물성연구팀

정 명 화

Contents

• DC measurement : Electrical resistanceH ll ff t ( l l i: Hall effect (normal, anomalous, spin

Hall)& simultaneous MR curve

• AC measurement: dV/dI measurement

& simultaneous I-V curve• Sample preparation

• RF measurement: Van der Pauw method

• Sample preparation

vs. timevs. frequency

Sample preparation

• Applications: Waveguide structure

: Magnetic rf oscillator: Magnetic rf oscillator: Spin diode: Domain wall motion

DC measurement

Current bias Voltage bias

V = I Rsmall

V = I Rlarge

control

measure

gcontrol

measure

I

V

Four-probetechnique

Two-probetechnique I

V

Itechnique

I

technique I

I

VV

I

Hall effect

F = q v X B ; Lorentz forceF q v X B ; Lorentz force

For a bar-shaped semiconductor,H ll ffi i t

B

Hall coefficient

RH = |VH | d

I B

- - - - - - - - - - - -

+ + + + + + + + + +ICarrier density

I B

VH n = I B

q |VH | d

VH < 0 : n-type

V > 0 p type

Hall mobility

μ =|VH | d

VH > 0 : p-type μ ρ I B

Hall measurement

Four-probe technique Five-probe technique

I+ I-

V-

I+ I-

V-

I+ I-

V-

I+ I-

Va+ Vb+

I+ I

V+ B B

I I

V+ B

V+(Va+) – (Vb+) = 0VTot = VH + VMR

offset

Hall bar-shaped filmHall bar-shaped film

Vb- Vc-Va- HallVH = (Va+) – (Vb–)

I+ I-

H ( ) ( )

MRVMR = (Va+) – (Vc+)

Vb+ Vc+Va+ B or (Va–) – (Va–)

Hall and MR measurement

I+ V-

RRT

V+ I-

R MR + RMR

RT = MR + RH

RT(+) = MR + RH

R ( ) MR RRHRT(−) = MR − RH

RT(+) + RT(−)MR = H

H

MR 2

RT(+) − RT(−)RH =

H

RH 2

Sample preparation

Cloverleaf

For an arbitrarily shaped sample,

CloverleafSquare or rectangle

Preferred Acceptable Not recommended

• Ohmic contact quality

• Sample uniformity

Important concerns

• Permanent magnet

C t

Equipment required

Sample uniformity

• Sample size ≫ contact size &

sample thickness• I < (200 R)-0.5

• Current source

ex. GaAs (ρ ~ 107 Ωcm) : 1nA

• High impedance voltmeter

• Measurement consistency • Temperature controller

Van der Pauw technique

Resistivity measurement Hall measurement

R V / I

I V1 4 VRA = V43 / I12

2 3

I

I1 4

I

V

1 4

RB = V14 / I23

2 3

B2 3

B 14 23

exp(-π RA/RS) + exp(-π RB/RS) = 1 I13 (1 → 3) : V = VH = V24P

n = I B

q |VH |dρ = RS d |VH | d

μ = | H |ρ I B

Example of typical dataExample of typical dataExample of typical data

1

2 3

4

Resistivity Hall voltage2 3

I21 V34 R21,34 .I12 V43 R12,43 .I43 V12 R43 12 .

+B fieldI13 V24P .I31 V42P .43 12 43,12

I34 V23 R34,23 .

I32 V41 R32,41 .I V R

31 42PI42 V13P .I24 V31P .

B fieldI23 V14 R23,14 .I14 V23 R14,23 .I41 V32 R41,32 .

−B fieldI13 V24N .I31 V42N .I42 V13N .42 13NI24 V31N .

exp( π R /R ) + exp( π R /R ) = 1

RB .RA .

n = 8 I B / q | ΣV |

RS = . nS = .

exp(-π RA/RS) + exp(-π RB/RS) = 1 nS = 8 I B / q | ΣVi |

μ = 1 / q nS RS = .ρ = RS d = . n = nS / d = .

Anomalous Hall effect

VH = (R0H + R1M) I / t

extraordinary Hall

ordinary Hall

y(anomalous Hall)

30

DMS thin film

1

unit

)

10

20

cm3

) R1

R0

1

0

RH (

arb.

20

-10

0

M (

emu/

0

-2 -1 0 1 2

-1

H ( T )

-2 -1 0 1 2-30

-20

H ( T ) H ( T )( )

Spin Hall effect

AC measurement

V

& simultaneous I-V curve

Waveform synthesizer

VO

DC signal → I – V curve

Mixer/adder Standard resistor Sample

R R

Vacsinωt

Lock-in amplifierI

V

RSR RS

VSR VSVO + Vacsinωt

RSRIO + RSRIacsinωtVS(IO) + ·Iacsinωt

dVS

dIVS(IO) IacsinωtdI I = Io

AC signal → dV/dI curveAC signal → dV/dI curve

RF measurement

DC source

DC

70x130 nm2

Bottom electrode

Ground

Bias teeDC

70x130 nm2

Top electrodeSignal

RF

RF + DC

MSUGround

RF

Oscilloscope Spectrum Analyzer

RF measurement

DC source

DC Bottom electrode

Ground

Bias teeDC

100x200 nm2

Top electrodeSignal

RF

RF + DCAISTGround

RF

Oscilloscope Spectrum Analyzer

RF measurement

DC source

DC Bottom electrode

Ground

Bias teeDC

W = 500 nm

Top electrodeSignal

RF

RF + DC

KISTGroundRF

Oscilloscope Spectrum Analyzer

Remarks for RF measurement

• You have to measure background signal.g g

• You have to use rf preamplifier.

0.6

0.7

Experimental data

500

400

0.4

0.5

μV/H

z-1/2 ) Experimental data

B k d i l

400

300

age

()

킮

With preamp.

0 1

0.2

0.3

PS

D ( μ Background signal

E B k d

200

100V

olta

0 2 4 6 8 100.0

0.1

Frequency ( GHz )

Exp.- Background 100

2520151050

Frequency (GHz)

Without preamp.

Frequency ( GHz ) Frequency (GHz)

Constant voltage mode

-I

RF pre-amp55dB

Bias-T55dB

up to 18 GHz

1kΩMagnetic SpectrumAnalyzer

1kΩMagnetic Field

Ru (0.85)+

D.C. bias voltage1.5 V battery

unit : nm e-

Constant current mode

Bias-Te-

RF pre-amp55dB

e

55dBUp to 18 GHz

i

Constant

SpectrumAnalyzer

Magnetic Field

Ru (0.85) VoltmeterConstant

Current SourceI = 1 mA

unit : nm+I

Field dependence of magnetic noise

A14

I = -1.25 mA

300 K

Current dependence of magnetic noise

H = 60 Oe

Temperature dependence of magnetic noise

8

300 K -100 Oe

2 )

H > Hc H < Hc

4

6

4.2 K, -100 Oe150 K, -100 Oe300 K, 100 Oe

( nV

/Hz1/

2

2

4

oise

PS

D

0 4 8 12 160N

o

Frequency ( GHz )

RF measurement with sweeping current & measuring dV/dI

Lock-in ref.1 009 kHz1.009 kHz

Magnetic rf oscillation

Current and field dependence of magnetic rf oscillation

Current = 14 mA (T = 3 K) Magnetic field = 6.1 kOe (T = 3 K)

Magnetic rf oscillator I

DC+RF RF

Bias tee

RF pre-amplifier

DC bias

DC

SpectrumAnalyzer

DC biasvoltage

H

Analyzer

Output(0.8~1.2 T)

F. B. Mancoff et al. Nature 437,393 (2005)

Magnetic rf oscillator II

RF

RF pre-

Bias teeDC

RF preamplifier

SpectrumAnalyzer

IA

75o

Output

Analyzer

IBH

Bias teeDC(740 mT)

RF

S. Kaka et al. Nature 437,389 (2005)

Spin diode

AIST

RFDC

AIST

(200 MHz~15 GHz)(200 MHz 15 GHz)

Output

A. A. Tulapurkar et al. Nature 438,339 (2005)

Domain wall motion

50 Ω

RF pre-amplifier

OscilloscopeH

Bi t

Pulsegenerator Output

Bias tee

Idc With field

M. Hayashi et al. Phys. Rev. Lett. 96, 197207 (2006)

Magnetic Property Measurement System

2008.12.

System performance examples

In 10 min. cooling from 300 K to stable 10 KRMS i < 4 X 10 8In 2 min. cooling from 10 K to stable 1.8 K RMS noise < 4 X 10-8 emu

Magnetic & transport measurement systems

+ Transport measurements (개발중)+ Transport measurements (개발중)for LR (~nV level) & HR (~100 fA level)materials

+ dV/dI (RS830)

2009. 1.

Memory switching time measurement system

+

• 4 probes

• CCD camera

• 3-axis magnetic field

• Each magnet ~ 1 kOe

• Vibration-free table

• Shield box

• Water cooled system

• High power supply

2008. 9.

Pulse pattern test

• Arbitrary waveform generator (120 MHz)

: Agilent 81150A

• Oscilloscope (1 GHz)

: Agilent 7104A: Agilent 7104A