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
MANSE Midterm Review
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
MANSE Midterm Review
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
MANSE Midterm Review
— 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)
MANSE Midterm Review
Introduction
Junctions & Devices
Metallic Structures
(Non GMR)
Direct Spin Injection
Detection
Anomalous
Magnetoresistance
Structures (In-plane
Anisotropy)
Spontaneous Hall
Effect Structures &
Metal-Semiconductor
Contacts
Magnetic Field Effects
Theory
&
Experiment
Large Area Junctions
Electronic &
Magnetic Response
Sensors (Linear Response)
Low Barrier Height Junctions
for Spin Injection
Perpendicular
Anisotropy &
Domain Wall
Velocity
GMR and TMR
Junctions
Small Area Junctions
MANSE Midterm Review
Field & Current Driven
Switching
Oscillatory &
High Frequency Response
Spin Injection – Spin-Self-Diffusion
P ˆ  P ˆ P ˆ
D 2 A
 CP  0
t
z
z
z
P  P0 exp( )
2
s
s  D sf
 sf
0
MANSE Midterm Review
Hence the spin diffusion
length is much greater
than the mean free path.
Direct Measurement of Injected
Polarisation
2 cm
Au
H, M
Al
η
Fe,Co,
Ni, Zn
Au Al Injector
+I
straw
z axis
λs
z
Z
Point spread function for single dipole at z
1.5 10
10
rc
1 10
10

Φ(Wb)
vy
k
vy lin
l
5 10
11
Line
j
X
0.04
0.03
0.02
0.01
0
5 10
0.01
0.02
0.03
0.04
Y+
+
-
•Using a
commercial
second-order
gradiometer
system
11
z (m)
vx  vx lin   m
k
l j
1
• The magnetic background of the injectors is a major concern
MANSE Midterm Review
Magnetisation Profile
Theory & Experiment
6
13
p ferro R ti
Rr i
i
2
Injected
moment for
positive
electronic
current
Fe moment
2
pr paraR t 1
i
R l i 0.5
i
2
pl para
R l Ri r
i
i
0
0
1
4
Rr
i
2
Rl
i
R
i
0
0
λs=0.35 cm
2
0
24
3
4
2
3
1
2
1
z
0
0
z
(cm)
iz
1
2
3
4
1
2
3
4
4
3
2
right injection
1
2
3
4
Fe @ 100 mT, 1.8 K
3.0
2.5
Rp
i
Raw Voltage USQUID(V)
Rr
i
0
Rl
i
R pl
i
R pr
i
0
z
(cm)
i
3
1
0
1
z
i
left injection
4
Rt
i
2
+15 mA
-15 mA
0 mA
0 mA
2
2.0
1.5
1
Rt
i1.0
2
0.5
0
R l R r 0.0
i
i
1
0
depolarization
Rd
i
-0.5
1
-1.0
paramagnetism
-1.5
2
4
-2.0
2
0
4
3
2
1
0
z
i
1
2
3
4
3
1
2
2
1
3
0
z
Position i(cm)
4
•The injected magnetisation is small even for 100 % efficiency
MANSE Midterm Review
1
5
2
6
3
7
4
8
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
…
MANSE Midterm Review
Various Aspects of the Observed Effects
2
0.00002
0.00001
0.00000
-0.00001
-0.00002
antisymmetric, ± H
-0.00003
1.6
1.4
8
3
0.00003
Abs. Symmetric Response S x 10 , Am
2
0.00004
Scaled Response x 10 Am
symmetric, - H
0 mA bkgnd H+
10 mA asym H+
10 mA sym H +
0 mA bkgnd H 10 mA asym H 10 mA sym H -
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
-0.00004
0
1
2
3
4
5
Position (cm)
6
7
2
10
100
Temperarure T, K
symmetric, + H
Symmetries of the Effects
Temperature Dependence
12
10
AC Out of Phase Amplitude
Linear Fit
10000
antisymmetric (mutual inductance)
symmetric (heating, injection ...)
8
Peak Magnetic Moment Density mz x 10 , Am
1
8
8000
Magnitude (a. u.)
8
6
4
6000
4000
2000
2
0
0
0
5
10
15
20
25
30
35
0
40
Current Amplitude IDC, mA
20
40
60
80
100
Magnetic Field (mT)
Current Dependence
Field Dependence
MANSE Midterm Review
0.4
10
Scaled current response x 10 , Am
2
AC rod sample - Fe @ 1.8 K, 20 mT
0.0
-0.4
-0.8
Zero bias
Positive bias
Negative bias
-1.2
0
2
4
6
8
Position (cm)
cross-induction
• Only cross-induction from the injection electrodes is observable
MANSE Midterm Review
Spin Injection
Conclusions
• 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
MANSE Midterm Review
AHE Sample, Setup and Specs
~ 100 mA
2 kΩ
40 dB
-100 dBV
V
20 kΩ
-100 dB
± 1.2 T
40 dB
V
60 dB
Real-Time
Digital
Oscilloscope
•
•
•
•
•
•
•
•
•
•
•
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
MANSE Midterm Review
CoFe/Pt Domain Topology
2 μm, 5 μm
1 μm, 2 μm
500 nm, 1 μ m
MANSE Midterm Review
400 nm, 500 nm 200 nm, 200 nm
M,UAHE vs μoH without Exchange Bias
T = 300 K
AHE Voltage (V)
6
Top Cross
5
4
3
2
1
7
5
4
3
2
4
-7
3
Bottom Cross
2
1
0
-1
-2
-3
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
-8
Bottom Cross
-9
-10
-11
-12
-13
-0.20
0.20
Top Cross
6
0
AHE Voltage (V)
AHE Voltage (V)
AHE Voltage (V)
7
-0.15
Magnetic Field (T)
•
•
•
Symmetric with ± B
Reversal through multiple domain
states, NOT a single nucleationpropagation event
DC Bias offsets
-0.10
-0.05
0.00
0.05
0.10
0.15
0.20
Magnetic Field (T)
•
•
•
•
Asymmetric with ± B
Reversal may be through a single nucleationpropagation event
Advantageous to come back from the EB
direction
Opposite EB directions on the two crosses
MANSE Midterm Review
Example without Exchange Bias
• Independent
reversal at the
two crosses
• Field-sweep-rate
determined time
delay
• Large number of
events
• Small induction
effects
10
AHE Voltage (V)
5
0
Bottom Cross
Top Cross
Bottom Filtered
Top Filtered
-5
-10
-15
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
Time (s)
MANSE Midterm Review
Example with Exchange Bias
• Correlated
reversal on the
two crosses
• Field-sweep-rate
independent time
delay
• Small number of
evens
• Negligible
induction effects
AHE Voltage (V)
8
6
4
2
0
Top Cross
Bottom Cross
-2
Filtered AHE Voltage (V)
-4
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-0.02
Top Cross
Bottom Cross
-0.01
0.00
0.01
0.02
0.03
Time (s)
MANSE Midterm Review
0.04
Schottky Barriers
Current 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.
MANSE Midterm Review
Schottky Barriers
Simple Models
The Schottky Model
q 2 Dn Nc
Jn 
kT
2q(b  Va ) N d
s
 qb  
 qVa  
exp  
 exp 
  1
 kT  
 kT  
The Bethe Model
4 qmc*k 2 2
 qb  
 qVa  
Jn 
T exp  
 exp 
  1
3
h
 kT  
 kT  
The Sze Model
qNc vr
 qb  
 qVa  
Jn 
exp  
exp 
 1



vr
 kT  
 kT  
1
vd
MANSE Midterm Review
Schottky Barriers
Effective Circuit
Rl
Cj
+Out
-Out
Rr
Rs
Ddd
Dti
Schottky
Junction
• 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
MANSE Midterm Review
Schottky Barriers
Magnetic Field Effects
g m B B
Thermionic-emission: MC  
metal
kT
c gs B B
semiconductor
MC   s
kT
gs B B
MC   s
Drift-diffusion:
2qb
* 2 Va r
Ambipolar diffusion: MC  (  )
B
2
xd
c
m
Recombination:
( g c  g v ) B B
MC  
2kT
MANSE Midterm Review
CoFe1
CoFe2
0.008
0.006
0.004
0.002
0.000
-4
-2
0
2
CoFe
0.0005
Difference in Differential Conductances
OUT - IN
Differantial Conductance s , S
Schottky Barriers
Derivative Spectroscopy CoFe/Si<111>
4
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0.0000
-0.0005
-0.0010
-0.0015
-0.0020
-0.0025
-6
-4
-2
0
2
4
6
4
5
Voltage U, V
0.7
0.5 T
1T
1.5 T
2T
2.5 T
3T
3.5 T
4T
4.5 T
5T
5.5 T
0.6
0.000
Derivative Deviation (mVRMS)
Difference in Differantial Conductance
Voltage U, V
-0.001
-0.002
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
-0.2
-0.3
-0.4
-0.003
-5
-4
-3
-2
-1
0
1
2
3
4
5
-1
0
1
2
3
Voltage Bias UDC, V
Voltage U, V
MANSE Midterm Review
T
T
T
T
T
T
T
T
T
T
T
T
0.013
0.012
Cu
Cu1
Cu2
0.011
0.0022
Difference in Differential Conductances
OUT - IN
Differantial Conductance s , S
Schottky Barriers
Derivative Spectroscopy Cu/Si <111>
0.010
0.009
0.008
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0.000
-5
-4
-3
-2
-1
0
1
2
3
4
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0.0020
0.0018
0.0016
0.0014
0.0012
0.0010
0.0008
0.0006
0.0004
0.0002
-6
5
-4
-2
Voltage U, V
2
4
6
0.14
0.006
0.12
Derivative Deviation (mVRMS)
Difference in Differential Conductances
0
Voltage U, V
0.005
0.004
0.003
0.002
0.001
0.10
0.08
0.06
0.04
0.02
0.00
-0.02
0.5 T
1T
1.5 T
2T
2.5 T
3T
3.5 T
4T
4.5 T
5T
5.5 T
-0.04
-0.06
-0.08
-0.10
-0.12
-0.14
-0.16
0.000
-5
-4
-3
-2
-1
0
1
2
3
4
5
-5
-4
-3
-2
-1
0
1
Voltage Bias UDC, V
Voltage U, V
MANSE Midterm Review
2
3
4
5
T
T
T
T
T
T
T
T
T
T
T
T
Schottky Barriers
Photo-illumination
metal
+++
semiconductor
front illmination
back illumination
(1) 
0
h
I0
h
I0
ohmic contact
h
I
---
Ec
EF
(2)
A
Ev
d
V
metal
semiconductor
• Illumination eliminates the
need for external biasing
Iaux
Iph
• The contribution of the series
magneto-resistance of the
diode base is strongly
diminished
D
Rs
V
(a)
MANSE Midterm Review
Rs
D
V
(b)
Schottky Barrier
Magneto-Photo-Voltaic Effect ?
0.50
AuSi @ 61 K
0.45
b  lim VOC (h )
0.40
Photovoltage Uph, V
0.35
I g* ( ) 0
CoSi @ 61 K
0.30
0.25
0.20
AuSi @ 300 K
b  lim VOC ( I )
0.15
I  ,T 0
0.10
CoSi @ 300 K
0.05
0.00
0
10
20
30
40
50
60
70
80
90
100
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
MANSE Midterm Review
Schottky Barriers
Magneto-Photo-Voltaic Effect
5
6
Magneto-Photo-Voltaic Effect MPV, %
100 K
Magneto-Photo-Voltaic Effect MPV, %
5
0
-5
-10
MPV % / T @ T = 100 K
Co 0.33(1)
Au 0.024(4)
Fe -1.23(4)
Ag 0.12(1)
-15
4
3
2
1
0
200 K
-1
-2
-3
-4
MPV % / T @ T = 200 K
Co 0.126(8)
Au 0.014(9)
Fe -0.512(8)
Ag 0.377(6)
-5
-6
-7
-8
-9
0
2
4
6
8
10
12
14
0
2
Magnetic Field 0H, T
Metal / Si
(% / T) 100K
4
6
8
10
12
14
Magnetic Field 0H, T
(% / 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
MANSE Midterm Review
Schottky Barriers
Photovoltaic 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
MANSE Midterm Review
R3D – GdCo2
5.4
Ni
Electron work function , eV
5.2
Co
5.0
4.8
Cu
Cr
4.6
Ti
4.4
Fe
V
4.2
Mn
4.0
Zn
3.8
Sc
3.6
3.4
20
21
22
23
24
25
26
27
28
29
30
31
Atomic number Z
-20
10
o
Y annealed at 1000 C
R0 = 10.9 
ln (I0.2 V)
Current (mA)
5
0
-30
GdCo2
-40
0.641(2) eV
0.192(3) eV
-50
-60
-70
-5
-80
-90
-10
-0.10
-0.05
0.00
Voltage (V)
0.05
0.10
0.000
0.005
0.010
0.015
0.020
Inverse Temperature 1/T, 1/K
MANSE Midterm Review
0.025
0.030
MTJ Optimisation
MANSE Midterm Review
Tunnel Junction Fabrication
1 ) Bottom contact patterning:
UV lithography + 45o Ar+ Ion Milling
4) Lift off: Ar+ Ion Milling (5o) +
Hot Ultrasonic for 5-6 hours
in remover
2) Pillar patterning:
E-Beam lithography +
Ar+ Ion Milling (85o + 5o)
5) Top Contact deposition:
UV lithography +
Sputtering (Ta5/Cu100nm)
+ lift off
3) Sputtering SiO2 Deposition
(100 nm)
MTJ stack
Ebeam Resist
SiO2
Cu contact
MANSE Midterm Review
Tunnel Junctions
Derivative Spectroscopy
V(J, H)
θ=0o
dV/dJ(J, H)
J
H
θ=0o
d2V/dJ2(J, H)
J
H
θ=0o
J
Annealed
H
As
Deposited
MANSE Midterm Review
Tunnel Barriers
Magneto-conductance
1.0
1.0
-barrier
0.5
0.5
0.0
MC
MC(Va)
0.0
-0.5
-1.0
-0.5
EF/q
-1.5
-1.0
-2
-1
0
1
2
-2.0
0.0
qVa/EF
Delta barrier
0.1
0.2
0.3
Va (V)
Realistic adiabatic barriers
MANSE Midterm Review
0.4
0.1 V
0.2 V
0.3 V
0.5
0.4
V
0.5 V
Tunnel Junctions
Micromagnetic Effects
90
16
12
10
2
Parameters:
off = 4.970(6) mV
A = 8.51(2) mV
Ha = 315(1) mT
8
Field (mT)
200
100
50
20
10
5
2
1
< 0.5
60
12
+ A cos[atan(H / Ha)]
10
120
o
14
Model:
Vac = off +
Derivative Voltage (mV)
Derivative Voltage (mV)
14
 = 20
2
R = 0.9995
6
30
150
8
6
4
2
0
180
0
2
4
6
8
330
210
10
12
4
-3
-2
-1
0
1
2
3
14
240
16
Magnetic Field 0H, T
300
270
Conventional magnetisation
reversal process in exchange
biased junction
Small angle deviations of
the electrodes
MANSE Midterm Review
Tunnel Junctions
The High Field Limit
0.014
Deriative Voltage (V)
0.013
14 T
10 T
7T
5T
2T
1T
0.5 T
CoFeB Annealed
Field Out Of Plane
0.012
0.011
0.010
0.009
0.008
0.007
0.006
0.005
0
25
50
75 100 125 150 175 200 225 250 275 300 325 350
Angle , deg
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?
MANSE Midterm Review
Tunnel Barriers
High Field TAMR?
0o
0o
10 T
14 T
10 T
Angle θ
Angle θ
Annealed
360 o
360 o
0o
0o
7T
D iffSRegBin
T
Angle θ
T
D iffSRegBin
5T
7T
Angle θ
T
5T
T
D iffSRegBin
D iffSRegBin
360 o
360 o
-0.5
Applied Voltage (V)
+0.5
-0.5 V
Applied Voltage (V)
As deposited
14 T
-0.5
+0.5
Applied Voltage (V)
+0.5
-0.5
Applied Voltage (V)
+0.5
• Detail appears in the derivative spectra only after the constant derivative
background hasD iffSRegBin
been subtracted D iffSRegBin
D iffSRegBin
D iffSRegBin
• 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
T
T
T
MANSE Midterm Review
T
Tunnel Barriers
TAMR Base Function?
Annealed
T=2K
Annealed
T = 10 K
Unannealed
T=2K
Unannealed
T = 10 K
Difference Voltage (V)
25
0
14 T
10 T
7T
5T
25
0
-100
-50
0
50
-50
Current (A)
MANSE Midterm Review
0
50
100
Tunnel Barriers
TAMR Fit?
14 T 2 K
Total
Peak 1
Peak 2
Peak 3
Peak 4
Peak 5
Peak 6
30
2K
Difference Voltage (V)
25
20
15
10
5
0
30
20
15
10
0
-5
-10
-10
-15
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
10 K
5
-5
-15
-0.8
5 T 10 K
Total
Peak 1
Peak 2
Peak 3
Peak 4
Peak 5
25
Difference Voltage (V)
35
-20
-0.8
-0.6
DC Bias (V)
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
DC Bias (V)
• 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.
MANSE Midterm Review
Tunnel Barriers
No Effect in the Plane
0.5 T
1.0 T
14.0 T
0o
360 o
-0.7 V
+0.7 V
-0.7 V
+0.7 V
-0.7 V
+0.7 V
• One privileged direction only – after crystallization
direction and the
T• The angle between
T
T the electron propagation
egBin
D iffSRegBin
D iffSRegBin
magnetisation remains constant
• Micromagnetic effects tend to dominate the low field transport
• Directional anisotropy is obvious – exchange bias
MANSE Midterm Review
Current Driven Switching
TMR Junctions
Nano-pillar
x = 100 nm y = 200 nm
R
TMR
40
1200
RA = 18 m
1000
20
2
0
-150
-100
-50
0
50
100
150
200
80
1400
60
1200
40
1000
20
0
800
-1.0
-0.5
0.0
External Magnetic Field (mT)
-20
1.0
0.5
Current (mA)
1.0
HEB , Hext, Hd
0.5
Mfree
120
100
Voltage (V)
800
-200
0H = 5 mT
x
0.0
-0.5
-1.0
-1.0
-0.5
0.0
Current (mA)
MANSE Midterm Review
0.5
1.0
TMR (%)
1400
TMR (%)
60
Resistance
TMR
1600
80
1600
140
1800
100
1800
Resistance ()
120
Resistance ()
2000
Tunnel Junctions
Conclusions
• 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
MANSE Midterm Review
Sensors (Linear Response)
GMR Junctions
Ta5/CoFe1.5/Cu2.8/ CoFeX / RuY / CoFeZ /Cu2.8/CoFe2.5/IrMn10/Ta5
10
X = 1.0, Y = 0.8, Z = 1.6
X = 1.6, Y = 0.8, Z = 1.0
8
Magnteoresistance (%)
GMR Ratio (%)
8
6
4
2
6
4
2
0
-2
SAF Moment Maintained
-4
0
-80
-40
0
40
80
-100
-50
0
50
100
H (Field (mT))
Field (mT)
• 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
MANSE Midterm Review
Sensors (Linear Response)
TMR Junctions
35
400
R
TMR
380
30
25
~ 6 /mT
~ 2 %/mT
Nominal Res. ~ 340 
Linear Region ~ 8.5 mT
Centered at
~ 6 mT
340
20
15
10
320
5
300
-200
Nano-pillar
x = 209 nm, y=122 nm
-150
-100
-50
0
0
50
100
External Magnetic Field (mT)
HEB
Mfree
Hext, Hd
MANSE Midterm Review
150
200
TMR (%)
Resistance ()
Max. Slope
360
Oscillatory &
High Frequency Response
5.0
Bias T
4 GHz
4.5 GHz
4.0
Device
Detected DC Voltage (V)
4.5
3.5
3.0
2.5
5 GHz
2.0
MW
Source
Idc
1.5
1.0
0.5
450
0.0
0
100
200
300
400
500
400
H (Oe)
-6
3.5x10
350
-6
3.0x10
300
2.5x10
H (Oe)
Induced DC Voltage (V)
-6
-6
2.0x10
250
200
-6
150
-6
100
1.5x10
1.0x10
50
-7
5.0x10
0
3
0.0
4
5
6
7
Microwave Frequency (GHz)
0
5
10
15
Input Microwave Power (mW)
20
MANSE Midterm Review
8
Conclusions
 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
MANSE Midterm Review
Future work
 Noise setup
 Stripline setup
 High resolution planar and volume GQUID gradiometers
 Electric field gated spin electroinic devices
MANSE Midterm Review
Outline
MANSE Midterm Review