IV Phenomena and Devices

MANSE Midterm Review

IV Phenomena and Devices

Direct detection of spin injection All-Metal structures and Domain Wall Velocity The magnetophotovoltaic effect in Schottky junctions MgO barrier magnetic tunnel junctions

Planned work


Staff, Publications

• Plamen Stamenov Postdoc from November 2007• Huseyin Kurth Postdoc• Tomohiko Niizeki Postdoc• Gen Feng Postdoc • Ciaran Fowley Postgrad• Cathy Boothman Postgrad• Kaan Oguz Postgrad


Publications;— On the direct magnetic detection of spin injection and adiabatic depolarisation in aluminium, P. Stamenov and JMD Coey, Journal of Magnetism and Magnetic Materials, 320, 403-406 (2008)—Influence of annealing on the bias voltage dependence of tunnelling magnetoresistance in MgO double-barrier magnetic tunnel junctions with CoFeB electrodes, G Feng, S van Dijken and J.M.D. Coey, Applied Physics Letters 89 162501 (2006)

—Effect of barrier sputtering parameters on Co80 Fe10 B10 – MgO magnetic tunnel junctions G. Feng, S. van Dijken and J. M. D. Coey, J. Magnetism Magnetic Materials 316 E984-986 (2007)—Noise in MgO barrier magnetic tunnel junctions with CoFeB electrodes; influence of annealing temperature, J. Scola, H Polovy, C. Fermon, M. Pannetier-Lecoeur, G. Feng, K. Fahy and J. M. D. Coey, Applied Physics Letters 90 252501 (2007)

—High inverted tunneling magnetoresistance in MgO –based magnetic tunnel juctions, J. F. Feng, Gen Feng, J. M. D. Coey, X.F. Han, and W.S. Zhan. Applied Physics Letters 91 102505 (2007)

— Room-temperature magnetoresistance in CoFeB/STO/CoFeB magnetic tunnel junctions, K. Oguz and J. M. D. Coey, Journal of Magnetism and Magnetic Materials, (2008)

— Magnetic annealing of CoFeB/MgO based single and double tunnel junctions: tunnel magnetoresistance, bias dependence and output voltage, G. Feng, S. van Dijken, J.M.D. Coey, T. Loo and D.J. Smith. Journal of Applied Physics, 105 (2009) in press


— An approach to fabricate pure metallic Ni-Ni and metallic oxide Ni-NiO-Ni nanocontacts by a repeatable microfabrication method, H X Wei, T. X. Wang, H. Wang, X. F. Han, M. A. Bari and J. M. D. Coey, International Journal of Nanotechnology 4 21-31 (2007)

— Magnetoresistance in NiOx nanoconstrictions controlled by magnetic fields and currents, O.Cespedes, M. Viret, JMD Coey, Journal of Applied Physics, 103, 083901 (2008)

— Size-dependent scaling of perpendicular exchange bias in magnetic nanostructures, G Malinowski, M. Albrecht, I. L. Guhr, J. M. D. Coey and S. van Dijken, Phys. Rev. B 75 012423 (2007)

— Reply to Comment on ‘Size-dependent scaling of perpendicular exchange bias in magnetic nanostructures’ , G. Malinowski, M. Albrecht, I.L. Guhr, J.M.D. Coey. S. van Dijken, Physical Review B 77 017402 (2008)

— Magnetic dead layers in sputtered Co40Fe40B20 films, K. Oguz, P. Jivrajka, M.Venkatesan, G. Feng, J.M.D. Coey, Journal of Applied Physics, 103, 07B526 (2008)

— Point contact Andreev reflection by nanoindentation of polymethyl methacrylate, E. Clifford and J. M. D. Coey, Applied Physics Letters 89, 092506 (2006)


Introduction

AnomalousMagnetoresistanceStructures (In-plane

Anisotropy)

Junctions & DevicesMetallic Structures

(Non GMR)Metal-Semiconductor

ContactsGMR and TMR

Junctions

Magnetic Field EffectsTheory

&Experiment

Spontaneous HallEffect Structures &

PerpendicularAnisotropy &

Domain WallVelocity

Low Barrier Height Junctionsfor Spin Injection

Small Area Junctions

Sensors (Linear Response)

Field & Current DrivenSwitching

Oscillatory & High Frequency Response

Large Area JunctionsElectronic &

Magnetic Response

Direct Spin InjectionDetection


Spin Injection – Spin-Self-Diffusion

2

2ˆ ˆˆ 0

P P PD A CP

t z z

0s

exp( )z

P P

s sfD

sf 0 Hence the spin diffusion length is much greater than the mean free path.


Direct Measurement of Injected Polarisation

Au Fe,Co, Ni, Zn

Al

2 cm

+ I

λs z

η

Au Fe,Co, Ni, Zn

Al

2 cm

+ I

λs z

η

Au Fe,Co, Ni, Zn

AlAu Fe,Co, Ni, Zn

AlAu Fe,Co, Ni, Zn

Al

2 cm

+ I

λs z

η + I

λs z

η

λs z

η

λs z

η

• The magnetic background of the injectors is a major concern

z axis

H, M

straw

Au Al Injector

z axis

H, M

straw

Au Al Injector

+ +

-

-

Z

X

Y

rc

vyk

vy linl

Linej

vxk

vx linl

jm

1

0.04 0.03 0.02 0.01 0 0.01 0.02 0.03 0.04

5 1011

5 1011

1 1010

1.5 1010Point spread function for single dipole at z

z (m)

Φ(Wb)vyk

vy linl

Linej

vxk

vx linl

jm

1

0.04 0.03 0.02 0.01 0 0.01 0.02 0.03 0.04

5 1011

5 1011

1 1010

1.5 1010Point spread function for single dipole at z

z (m)

Φ(Wb)

•Using a commercial second-order gradiometer system


Magnetisation ProfileTheory & Experiment

•The injected magnetisation is small even for 100 % efficiency

0 1 2 3 4 5 6 7 8-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Ra

w V

olta

ge

U

SQ

UID(V

)

Position (cm)

+15 mA -15 mA 0 mA 0 mA

Fe @ 100 mT, 1.8 K

0 1 2 3 4 5 6 7 8-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Ra

w V

olta

ge

U

SQ

UID(V

)

Position (cm)

+15 mA -15 mA 0 mA 0 mA

Fe @ 100 mT, 1.8 K

Rri

Rli

Ri

0

zi

4 3 2 1 0 1 2 3 44

2

0

2

4

6

Rri

Rti

2

Rli

Rti

2

Rli

Rri

0

zi

4 3 2 1 0 1 2 3 42

1

0

1

2

3

λs=0.35 cm

z (cm)

Rri

Rli

Ri

0

zi

4 3 2 1 0 1 2 3 44

2

0

2

4

6

Rri

Rti

2

Rli

Rti

2

Rli

Rri

0

zi

4 3 2 1 0 1 2 3 42

1

0

1

2

3

λs=0.35 cm

z (cm)

p ferroi

pr parai

pl parai

zi

4 3 2 1 0 1 2 3 40

0.5

1

z (cm)

Fe momentInjected moment forpositive electronic current

p ferroi

pr parai

pl parai

zi

4 3 2 1 0 1 2 3 40

0.5

1

z (cm)

Fe momentInjected moment forpositive electronic current

Rri

Rti

2

Rli

Rti

2

Rli

Rri

0

zi

4 3 2 1 0 1 2 3 42

1

0

1

2

3

Rpi

0

Rpli

Rpri

Rdi

zi

4 3 2 1 0 1 2 3 42

1

0

1

depolarizationparamagnetism

left injection right injection

Rri

Rti

2

Rli

Rti

2

Rli

Rri

0

zi

4 3 2 1 0 1 2 3 42

1

0

1

2

3

Rpi

0

Rpli

Rpri

Rdi

zi

4 3 2 1 0 1 2 3 42

1

0

1

depolarizationparamagnetism

left injection right injection


Why should it work? / Why should it not?• Long spin diffusion length – 3 nm (300 K) 300 μm (20 K) ~ 3 mm (2 K)• High polarisation of ferromagnetic

injectors – 40 %• Signal magnitude – Zeeman shift of

electrochemical potential is 0.1 meV/T, Spin injection shift 1 eVm/V (10-2 V/m achievable → ~ 10 meV)

• Spatial discrimination – fully decorrelated at 1 cm

• Short timescales (10 – 100 ns) – audio frequency modulation is possible

• Complications arising from injector stability and superconducting transitions (Al, In) are avoidable

• Small signals moments of ~ 10-9 Am2

• Small injection efficiencies ~ 5 %• Large background – 10 times the

signal• Background drifts – up to 100 %/min• High power dissipation levels – 10

mW/cm• Parasitic inductive pickup –

angular errors of 0.3 mm/10 cm – antisymmetric with respect to current

• Signal and noise spatial frequency spectrum overlap

• Unexpected effects, symmetric with respect to current

• …

• 1985 M. Johnson and R. H. Silsbee – electrical detection of the “Hanle Effect”

• 1993 M. Johnson – spin accumulation in Au

• …


Various Aspects of the Observed Effects

0 1 2 3 4 5 6 7 8-0.00004

-0.00003

-0.00002

-0.00001

0.00000

0.00001

0.00002

0.00003

0.00004

0 mA bkgnd H+ 10 mA asym H+ 10 mA sym H + 0 mA bkgnd H - 10 mA asym H - 10 mA sym H -

S

cale

d R

esp

on

se x

103 A

m2

Position (cm)

antisymmetric, ± H

symmetric, - H

symmetric, + H0 1 2 3 4 5 6 7 8

-0.00004

-0.00003

-0.00002

-0.00001

0.00000

0.00001

0.00002

0.00003

0.00004

0 mA bkgnd H+ 10 mA asym H+ 10 mA sym H + 0 mA bkgnd H - 10 mA asym H - 10 mA sym H -

S

cale

d R

esp

on

se x

103 A

m2

Position (cm)

antisymmetric, ± H

symmetric, - H

symmetric, + H

1 10 100

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Ab

s. S

ymm

etr

ic R

esp

on

se S x

108 ,

Am

2

Temperarure T, K

0 5 10 15 20 25 30 35 400

2

4

6

8

10

12

Pe

ak

Ma

gn

etic

Mo

me

nt D

en

sity

mz x

108 ,

Am

2

Current Amplitude IDC

, mA

antisymmetric (mutual inductance) symmetric (heating, injection ...)

0 20 40 60 80 100

0

2000

4000

6000

8000

10000

Ma

gn

itud

e (

a. u

.)

Magnetic Field (mT)

AC Out of Phase Amplitude Linear Fit

Symmetries of the Effects Temperature Dependence

Current Dependence Field Dependence


AC rod sample - Fe @ 1.8 K, 20 mT

0 2 4 6 8

-1.2

-0.8

-0.4

0.0

0.4

Sca

led

cu

rre

nt re

spo

nse

x 1

010 ,

Am

2

Position (cm)

Zero bias Positive bias Negative bias

cross-induction

• Only cross-induction from the injection electrodes is observable


Spin InjectionConclusions

• No spin injection or adiabatic electronic heating down to δM of the order of 1 A/m, current densities of 108 A/m2 and fields up to 0.5 T

• Non-trivial current, field and temperature dependencies for most observed effects

• Further work on custom-designed gradiometers


AHE Sample, Setup and Specs

• Spontaneous (Anomalous) Hall• [Pt1/Co0.5]3Pt2

• [Pt1/Co0.5]3IrMn10Pt2

• Size (0.1 – 0.3) x (10 - 500 μm)• DC – 50 MHz broadband• AC – 1-10 MHz LIA• Bmax = 200 mT, 1.2 T, 14 T• dB/dT = 200 T/s, 0.5 T/s, 13 mT/s• 2 K < T < 350 K• I max < 100 μA• VDW < 1000 m/s

V

V

Real-Time Digital

Oscilloscope

40 dB

40 dB

60 dB -100 dBV

-100 dB

~ 100 mA

20 kΩ

2 kΩ

± 1.2 T


CoFe/Pt Domain Topology

2 μm, 5 μm 1 μm, 2 μm 500 nm, 1 μ m 400 nm, 500 nm 200 nm, 200 nm


M,UAHE vs μoH without Exchange BiasT = 300 K

-0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20

-3

-2

-1

0

1

2

3

4

0

1

2

3

4

5

6

7

Bottom Cross

AH

E V

olta

ge

(V

)

Magnetic Field (T)

Top Cross

AH

E V

olta

ge

(V

)

• Symmetric with ± B• Reversal through multiple domain

states, NOT a single nucleation-propagation event

• DC Bias offsets

-0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20-13

-12

-11

-10

-9

-8

-7

2

3

4

5

6

7

AH

E V

olta

ge

(V

)

Magnetic Field (T)

Top Cross

AH

E V

olta

ge

(V

)

Bottom Cross

• Asymmetric with ± B• Reversal may be through a single nucleation-

propagation event• Advantageous to come back from the EB

direction• Opposite EB directions on the two crosses


Example without Exchange Bias

-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2-15

-10

-5

0

5

10

AH

E V

olta

ge

(V

)

Time (s)

Bottom Cross Top Cross Bottom Filtered Top Filtered

• Independent reversal at the two crosses

• Field-sweep-rate determined time delay

• Large number of events

• Small induction effects


Example with Exchange Bias

-0.02 -0.01 0.00 0.01 0.02 0.03 0.04

-4-3-2-101234567

-4

-2

0

2

4

6

8

Top Cross Bottom Cross

Filte

red

AH

E V

olta

ge (

V)

Time (s)

AH

E V

olta

ge (V

)

Top Cross Bottom Cross

• Correlated reversal on the two crosses

• Field-sweep-rate independent time delay

• Small number of evens

• Negligible induction effects


Schottky BarriersCurrent Components

a) Thermionic emission over the barrier

b) Tunneling through the barrier

c) Recombination in the space-charge region

d) Recombination in the neutral region

After: Rhoderick, E.H. & Williams, R.H. (1988).Metal-Semiconductor Contacts. Oxford: Clarendon.


Schottky BarriersSimple Models

c r

r

d

exp exp 11

b an

qN v q qVJ

v kT kTv

2 2 ( )exp exp 1n c b a d b a

ns

q D N q V N q qVJ

kT kT kT

* 22

3

4exp exp 1c b a

n

qm k q qVJ T

h kT kT

The Schottky Model

The Bethe Model

The Sze Model


Schottky BarriersEffective Circuit

R s D d d D t i

R l

R r -O u t+O u t

SchottkyJunction

C j

• The far from simple effective circuit of the real diode makes the analysis of all possible magnetic field effects difficult• The extraction of spin polarisation information is, by necessity, model dependent


Schottky BarriersMagnetic Field Effects

Thermionic-emission: c m Bm

g BMC

kT

c s Bs

g BMC

kT

s Bs 2 b

g BMC

q

Drift-diffusion:

* 2 a r2d

( )V

MC Bx

Ambipolar diffusion:

c v B( )

2

g g BMC

kT

Recombination:

metal

semiconductor


Schottky BarriersDerivative Spectroscopy CoFe/Si<111>

-5 -4 -3 -2 -1 0 1 2 3 4 5-0.003

-0.002

-0.001

0.000

Dif

fere

nc

e i

n D

iffe

ran

tia

l C

on

du

cta

nc

e

Voltage U , V

-1 0 1 2 3 4 5-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Der

ivat

ive

Dev

iatio

n (m

VR

MS)

Voltage Bias UDC

, V

0.5 T 1 T 1.5 T 2 T 2.5 T 3 T 3.5 T 4 T 4.5 T 5 T 5.5 T


Schottky BarriersDerivative Spectroscopy Cu/Si <111>

-5 -4 -3 -2 -1 0 1 2 3 4 50.000

0.001

0.002

0.003

0.004

0.005

0.006

Dif

fere

nc

e i

n D

iffe

ren

tia

l C

on

du

cta

nc

es

Voltage U , V

-5 -4 -3 -2 -1 0 1 2 3 4 50.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

0.011

0.012

0.013

Dif

fera

nti

al

Co

nd

uc

tan

ce

,

S

Voltage U , V

Cu1 Cu2


Schottky BarriersPhoto-illumination

I p h

D

V

R s

I a u x

D

V

R s

(a) (b)

ohmic contact

back illumination

front illmination

hI0

V

A

semiconductormetal

0

(1)

(2)hI

hI0

semiconductormetal

- - -

+ + +

Ev

EF

Ec

d

• Illumination eliminates the need for external biasing

• The contribution of the series magneto-resistance of the diode base is strongly diminished


Schottky BarrierMagneto-Photo-Voltaic Effect ?

0 10 20 30 40 50 60 70 80 90 1000.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

AuSi @ 61 K

CoSi @ 61 K

AuSi @ 300 K

CoSi @ 300 K

Ph

oto

volta

ge

Uph

, V

Light Intensity I, %

• The photo-voltage does saturate as a function of the illumination light intensity at sufficiently low temperatures• The photo-voltage does become a good measure of the barrier height and can be used to extract spin polarisation

b OC, 0

lim ( )I T

V I

*b OC

( ) 0lim ( )gI

V h


Schottky BarriersMagneto-Photo-Voltaic Effect

0 2 4 6 8 10 12 14

-15

-10

-5

0

5

MPV % / T @ T = 100 K Co 0.33(1) Au 0.024(4) Fe -1.23(4) Ag 0.12(1)

M

ag

ne

to-P

ho

to-V

olta

ic E

ffect

MP

V, %

Magnetic Field 0H, T

0 2 4 6 8 10 12 14-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

MPV % / T @ T = 200 K Co 0.126(8) Au 0.014(9) Fe -0.512(8) Ag 0.377(6)

Ma

gn

eto

-Ph

oto

-Vo

ltaic

Effe

ct M

PV

, %


100 K 200 K

Metal / Si (% / T) 100K (% / T) 200 K α (%) 100 K α (%) 200 K

Co +0.33 +0.13 +25 +19

Fe -1.23 -0.15 -91 -76

Au +0.02 +0.01 +3 +2

Ag +0.12 +0.37 +8 +55


Schottky BarriersPhotovoltaic Measurements

• The Schottky barrier height should be sufficiently different from the band-gap of the semiconductor, to avail for experimental separation of the internal photoemission

• The metal layer should be sufficiently transparent at the frequencies of interest, but sufficiently thick to preserve bulk behaviour

• The temperature dependence of the Schottky barrier height should be sufficiently weak

• The Schottky barrier height should be determined by the difference of the work functions of the two materials and not by interface pinning


R3D – GdCo2

0.000 0.005 0.010 0.015 0.020 0.025 0.030

-90

-80

-70

-60

-50

-40

-30

-20

GdCo2

0.641(2) eV 0.192(3) eV

ln (I 0

.2 V)

Inverse Temperature 1/T, 1/K

20 21 22 23 24 25 26 27 28 29 30 313.4

3.6

3.8

4.0

4.2

4.4

4.6

4.8

5.0

5.2

5.4

Zn

Cu

NiCo

Fe

Mn

Cr

V

Ti

Sc

Ele

ctro

n w

ork

func

tion ,

eV

Atomic number Z

-0.10 -0.05 0.00 0.05 0.10-10

-5

0

5

10

Y annealed at 1000 oCR

0 = 10.9

Cur

rent

(m

A)

Voltage (V)


MTJ Optimisation


Tunnel Junction Fabrication

3) Sputtering SiO2 Deposition (100 nm)

4) Lift off: Ar+ Ion Milling (5o) + Hot Ultrasonic for 5-6 hours in remover

5) Top Contact deposition: UV lithography +

Sputtering (Ta5/Cu100nm) + lift off

MTJ stack

Ebeam ResistSiO2

Cu contact

2) Pillar patterning:E-Beam lithography +

Ar+ Ion Milling (85o + 5o)

1 ) Bottom contact patterning: UV lithography + 45o Ar+ Ion Milling


Tunnel JunctionsDerivative Spectroscopy

J J J

H H H

θ = 0 o V(J, H) dV/dJ(J, H) d2V/dJ2(J, H) θ = 0 o θ = 0 o

Annealed

AsDeposited


Tunnel BarriersMagneto-conductance

-2 -1 0 1 2-1.0

-0.5

0.0

0.5

1.0

MC

(Va)

qVa/E

F

-barrier

0.0 0.1 0.2 0.3 0.4 0.5-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

MC

Va (V)

EF/q

0.1 V 0.2 V 0.3 V 0.4 V 0.5 V

Delta barrier Realistic adiabatic barriers


Tunnel JunctionsMicromagnetic Effects

-3 -2 -1 0 1 2 34

6

8

10

12

14

Model:V

ac = off +

+ A cos[atan(H / Ha)]2

Parameters:off = 4.970(6) mVA = 8.51(2) mVH

a = 315(1) mT

R2 = 0.9995

De

riva

tive

Vo

ltag

e (

mV

)


0

2

4

6

8

10

12

14

16

0

30

60

90

120

150

180

210

240

270

300

330

0

2

4

6

8

10

12

14

16

= 20o

De

riva

tive

Vo

ltag

e (

mV

)

Field (mT) 200 100 50 20 10 5 2 1 < 0.5

Conventional magnetisation reversal process in exchange

biased junction

Small angle deviations of the electrodes


Tunnel JunctionsThe High Field Limit

0 25 50 75 100 125 150 175 200 225 250 275 300 325 3500.005

0.006

0.007

0.008

0.009

0.010

0.011

0.012

0.013

0.014

CoFeB AnnealedField Out Of Plane

De

ria

tive

Vo

ltag

e (

V)

Angle , deg

14 T 10 T 7 T 5 T 2 T 1 T 0.5 T

Is there any detail in the high field limit, when the magnetisations of junction electrodes are aligned parallel to each other and to the applied field?


Tunnel BarriersHigh Field TAMR?

DiffSRegBinT

DiffSRegBinT DiffSRegBinT

DiffSRegBinT

0 o

360 o

360 o

0 o

-0.5 +0.5 -0.5 V +0.5 Applied Voltage (V) Applied Voltage (V)

An

gle θ A

ngle θ

14 T 10 T

7 T 5 T

DiffSRegBinT DiffSRegBinT

DiffSRegBinT

-0.5 +0.5 -0.5 +0.5

360 o

0 o

360 o

0 o

Applied Voltage (V) Applied Voltage (V)

14 T 10 T

5 T

Angle θ

Angle θ

DiffSRegBinT

7 T

• Detail appears in the derivative spectra only after the constant derivative background has been subtracted• The symmetry of the effect is high and one base function should be sufficient to describe it• Unannealed junctions show at least three times lower amplitudes

Annealed

As

depo

site

d


Tunnel BarriersTAMR Base Function?

-100 -50 0 50

0

25

0

25

-50 0 50 100

UnannealedT = 2 K

Current (A)

AnnealedT = 10 K

14 T 10 T 7 T 5 T

D

iffer

ence

Vol

tage

(V

)AnnealedT = 2 K

UnannealedT = 10 K


Tunnel BarriersTAMR Fit?

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8-15

-10

-5

0

5

10

15

20

25

30

35 14 T 2 K Total Peak 1 Peak 2 Peak 3 Peak 4 Peak 5 Peak 6

Diff

ere

nce

Vo

ltag

e (V

)

DC Bias (V)

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8-20

-15

-10

-5

0

5

10

15

20

25

30

5 T 10 K Total Peak 1 Peak 2 Peak 3 Peak 4 Peak 5

Diff

ere

nce

Vo

ltag

e (V

)

DC Bias (V)

2 K 10 K

• The fit is a set of four Lorentzians of width 0.35 eV and approximately equivalent spacing of 0.25 eV, corresponding to the anisotropy of both spin-up and spin-down bands near the Fermi surface.


Tunnel BarriersNo Effect in the Plane

DiffSRegBinT DiffSRegBinT DiffSRegBinT

0 o

360 o

+0.7 V -0.7 V -0.7 V -0.7 V +0.7 V +0.7 V

0.5 T 1.0 T 14.0 T

• One privileged direction only – after crystallization• The angle between the electron propagation direction and the magnetisation remains constant• Micromagnetic effects tend to dominate the low field transport• Directional anisotropy is obvious – exchange bias


Current Driven SwitchingTMR Junctions

-1.0 -0.5 0.0 0.5 1.0

800

1000

1200

1400

1600

1800

Resistance TMR

Current (mA)

Res

ista

nce

()

0H = 5 mT

-20

0

20

40

60

80

100

120

140

TM

R (%

)

-200 -150 -100 -50 0 50 100 150 200800

1000

1200

1400

1600

1800

2000

R TMR

External Magnetic Field (mT)

Res

ista

nce

()

0

20

40

60

80

100

120

TM

R (%

)

Nano-pillar x = 100 nm y = 200 nm

RA = 18 m2

x

Mfree

HEB , Hext, Hd

-1.0 -0.5 0.0 0.5 1.0-1.0

-0.5

0.0

0.5

1.0

Vol

tage

(V

)

Current (mA)


Tunnel JunctionsConclusions

• Well characterized tunnel junctions with high TMR, good patterning and well-behaved micromagnetically

• There is high field anisotropy of the tunnelling magnetoresistance

• Origin is the anisotropy of the electronic structure

• The fundamental reason is spin-orbit coupling


Sensors (Linear Response)GMR Junctions

-80 -40 0 40 80

0

2

4

6

8

GM

R R

atio

(%

)

Field (mT)

-100 -50 0 50 100

-4

-2

0

2

4

6

8

10Ta

5/CoFe

1.5/Cu

2.8/ CoFe

X / Ru

Y / CoFe

Z /Cu

2.8/CoFe

2.5/IrMn

10/Ta

5

Mag

nteo

resi

stan

ce (%

)

H (Field (mT))

X = 1.0, Y = 0.8, Z = 1.6 X = 1.6, Y = 0.8, Z = 1.0

SAF Moment Maintained

• Reversal behaviour typical of exchange-biased spin-valves• It is possible to engineer structures where the SAF looses magnetic integrity at small external fields, therefore resulting in negative GMR ratios


Sensors (Linear Response)TMR Junctions

-200 -150 -100 -50 0 50 100 150 200

300

320

340

360

380

400

R TMR

External Magnetic Field (mT)

Res

ista

nce

()

Max. Slope ~ 6 /mT ~ 2 %/mT

Nominal Res. ~ 340 Linear Region ~ 8.5 mTCentered at ~ 6 mT

0

5

10

15

20

25

30

35

TM

R (%

)

Nano-pillarx = 209 nm, y=122 nm

HEB

Hext, Hd

Mfree


Oscillatory &High Frequency Response

0 100 200 300 400 5000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Det

ecte

d D

C V

olta

ge (V

)

H (Oe)

5 GHz

4.5 GHz

4 GHz

0 5 10 15 20

0.0

5.0x10-7

1.0x10-6

1.5x10-6

2.0x10-6

2.5x10-6

3.0x10-6

3.5x10-6

Ind

uce

d D

C V

olta

ge

(V

)

Input Microwave Power (mW)

3 4 5 6 7 80

50

100

150

200

250

300

350

400

450

H (

Oe

)

Microwave Frequency (GHz)

IdcMW

Source

Bias T

Device


Direct detection of spin injection will require materials with long spin diffusion lengths > 10 μm and optimized gradiometer assemblies

Technology of fabricating and nanoscale pattering of MgO barrier magnetic tunnel junctions has been mastered. Installation of CMP in Spring 2009 will improve yield

Optimized low-barrier height Schottky contacts still deserve a detailed investigation as spin-injectors

Working thin film stacks and devices based on charge transfer ferromagnetism has yet to be demonstrated

Conclusions


Future work

Noise setup Stripline setup High resolution planar and volume GQUID gradiometers

Electric field gated spin electroinic devices


Outline

IV Phenomena and Devices

Documents

Transcript of IV Phenomena and Devices