Designing Nanoscale Materials
Lecture Series by 2004 Debye Institute
Professor
Christopher B. Murray
IBM Research
Ornstein Laboratory 166
Office phone 253 2227
cbmurray@alum.mit.edu
Debye Lecture 6
Nanostructured Magnetic Materials for
Information Technology
C. B. Murray
Magnetic Nanocrystals and Nanocrystal Superlattices
Inorganic
C.B. Murray, S. Sun, F. X. Redl, K. S. Cho and W. Gaschler.
Core 1-15nm IBM T. J. Watson Research Center; Yorktown Heights, NY
(1)
Synthesize, characterize and integrate nanostructured materials.
(2)
Probe the limits conventional materials/device scaling.
(3)
Harness mesoscopic properties for future technology.
Surfactants (4)
1-4 nm thick
Film Growth:
Self-Assembly
Explore the potential of self-assembly for nanofabrication.
Nanocrystal Superlattice
A
Synthesis
B
250C
Annealed Superlattice
60 nm
Reagents
30 nm
C
Size Selective
Processing
D
80 nm
5 nm
Patterning & addressing
Applications & Opportunities for High Energy Product magnets.
Automotive and Avionic Components
Micro/Nano Devices
Medical diagnostic system
Various actuators
Hard disk drives in acoustic systems
Head actuators
•Single magnetic domain particles.
M (emu)
Superparamagnetism
5K
300K
•Orientation determined by anisotropy energy, K.
0.02
•Energy barrier, ∆E = KV / k BT
•Remnant magnetization, M rem
M rem (t ) = M sat e
−t / τ
0.04
0.00
where τ = τo e − KV / k T
•Blocking temperature, k BTB ≈ 25∆E
B
-4000
-2000
0
2000
H (G)
4000
-0.02
•At T >> TB , particles are superparamagnetic.
-0.04
•Zero hysterises – Langevin equation
• M ( H ) = coth(µH / k BT ) − k BT / µH
8nm MT Co
90 K
120 K
150 K
180 K
210 K
240 K
270 K
M (emu)
Energy
•At T << TB , particles are ferromagnetic.
0.04
0.02
∆E
0.00
-100
-50
0
-0.02
Orientation
-0.04
50
100
H/T (G/K)
8.00E-02
2.50E-03
6.00E-02
1.88E-03
Magnetic Moment (Emu)
Magnetic Moment (Emu)
Magnetization - size dependence
4.00E-02
2.00E-02
0.00E+00
-2.00E-02
-4.00E-02
6.25E-04
0.00E+00
-6.25E-04
-1.25E-03
-1.88E-03
-6.00E-02
-8.00E-02
-5000
1.25E-03
-3000
-1000
1000
3000
Magnetic Field (Gauss)
dipole interaction
no dipole interactions
10nm fcc-Co particles
5000
-2.50E-03
-5000
-3000
-1000
1000
3000
Magnetic Field (Gauss)
dipole interactions
no dipole interactions
2-2.5nm fcc-Co particles
50
Synthesis and Self-assembly of Co nanoparticles
•
•
•
High temperature (200 oC), solution phase synthesis.
Rapid nucleation – growth controlled by coordinating ligands.
Size distribution improved by size selective precipitation.
Film Growth :Self-Assembly
Nanoparticle Superlattice
Size selective precipitation
Annealed Superlattice
Synthesis of Transition Metal Nanocrystals
Co2+ + (Et)3BH + R3P + C17H19COOH
250C
Na+Napth-
Sequential reduction of metals Core/Shell
Mn+
Co2+ + C16(OH)2+R3P + C17H19COOH
Simultaneous reduction of metals alloys
Co2(CO)8 + R3P + C17H19C00H
CoM
Co2+ + Mn+
AA
60 nm
Co 8 nm
Ni 9 nm
Co/Ni 9 nm
FePt 4 nm
Crystal phases of Cobalt
3 crystal phases are studied..
Fcc and hcp differ only in stacking sequence
of close-packed layers.
fcc: ABCABC…
Hcp: ABABAB...
A
B
A
(1) hcp Co
C
B
A
(2) fcc Co
•Cubic unit cell
•Complex internal structure
Set I - 8 atoms
Set II - 12 atoms
(3) ε-Co
Dinega, D.P; Bawendi, M.G. Angew. Chem., 1999, 38(12), 1788.
XRD modeling of cobalt nanoparticles
Better fits obtained by including
–
–
•
•
Stacking faults
Twin faults
Introduction of stacking faults
generates mixed fcc/hcp structures.
Leads to the inter conversion of fcc
and hcp phases
A
A
A
A
B
B B
B
C
C C
fcc
75% fcc
Intensity
•
50% fcc
75% hcp
Twin Plane
A
A
A
B B
B
B
C C C
C
Stacking Fault
hcp
30
40
50
60
70
2θ
80
90
100
002
XRD Modeling of hcp nanoparticles
101
Intensity
4nm
6nm
8nm
50
2θ
60
70
110
40
100
Intensity
10nm
Expt.
Fit
35 nm
•
•
40
50
60
70
2θ
TEM images show that hcp Co nanoparticles are slightly prolate.
XRD fitting show extensive faulting/disorder.
–
–
Approximately one fault every 2.5 stacking planes.
Consistent across a variety of particle sizes.
80
90
40
50
60
311
70
2θ
50
80
55
2θ
60
Expt
Fit
90
65
100
520
45
510
40
420
330
321
211
Intensity
310
Intensity (arbitrary units)
221
3nm
5nm
7nm
9nm
70
111
XRD Modeling of fcc nanoparticles
Intensity
4nm
7nm
8nm
200
40
40
50
60
50
Expt.
Fit
70
80
2θ
60
90
2θ
•
•
TEM images show that fcc Co nanoparticles are
spherical in shape.
XRD fitting - one fault every 4 planes.
–
•
70
220
Intensity
20 nm
6nm
Bad fits at higher angles.
Dark regions in TEM imply “multiple twinned”
(MT) structures.
100
111
6nm
Intensity
Intensity (arbitrary units)
4nm
7nm
40
45
50
Expt.
Fit
40
50
60
70
2θ
80
55
2θ
60
65
70
220
200
8nm
90
100
XRD Modeling of MT polyhedra
•
Better fits have been reported for MT polyhedra
–
–
•
Highly faceted structures
Icosahedral, cubeoctahedral and decahedral structures suggested
HR-TEM images also suggest the presence of multiple domains
–
Consistent with multiple twinning
Decahedron
2.0 nm
Cubeoctahedron Icosahedron
Hall,B.D. et al., Phys. Rev. B, 1991, 43(5), 3906.
221
XRD Modeling of ε-Co nanoparticles
310
Intensity
3nm
5nm
7nm
50
60
2θ
70
70
420
510
Expt
Fit
60
80
90
520
50
330
211
40
40
321
311
Intensity
9nm
100
2θ
•
•
•
TEM images show that ε-Co forms as
spherical nanoparticles with narrow
size distributions.
XRD fits - perfect crystalline internal
structure.
Supported by HR-TEM images of
individual nanoparticles.
Modeling of the magnetization of Co nanoparticles
•Equilibrium partition function of nanoparticles in applied magnetic field.
ρ ρ − E ( Hρ , µρ,K ,V ) / k T
∫ dµθ ∫ dµϕ M sat ( µ • Hρ )e
< M >= ∫ dKp ( K ) ∫ dVp (V ) ∫ dH θ ∫ dH ϕ
ρ
− E ( H , µ , K ,V ) / k T
dµ
dµ
e
∫ θ∫ ϕ
ρ ρ
E / V = − M sat µ • H − KS z2
B
B
M rem (t ) = ∫ dKp ( K ) ∫ dVp (V )[αM sat e −t / τ ] where
τ = τ o e − KV / k T
B
Moment, µ
θ
Easy axis
Applied
Field
Magnetic modeling of MT Co nanoparticles
M (emu)
0.06
Saturation Magnetization (1 Tesla)
0.05
0.06
0.04
M (emu)
0.04
Expt.
Fit
0.02
0.03
For 0.1 T, only T>170 K in equilibrium
0.00
-10000
0.02
-5000
0
5000
-0.02
0.01
Remnant Magnetization (120 s)
-0.04
0.00
0
50
100
150
200
250
300
-0.06
T (K)
•
•
TEM analysis - 7 nm diameter
Magnetic fitting
–
–
•
•
•
Diameter
K
6.2 + 0.5 nm
7.0x105 + 3.5x105 ergs cm-3
Smaller “magnetic” diameter accounted for by the presence of oxide layer.
Anisotropy close to bulk fcc value
Remnant magnetization is half saturation magnetization at low temperatures
–
Implies uniaxial symmetry.
10000
H (G)
Magnetic modeling of MT Co nanoparticles
M (emu)
0.06
Saturation Magnetization (1 Tesla)
0.05
0.06
0.04
M (emu)
0.04
Expt.
Fit
0.02
0.03
For 0.1 T, only T>170 K in equilibrium
0.00
-10000
0.02
-5000
0
5000
-0.02
0.01
Remnant Magnetization (120 s)
-0.04
0.00
0
50
100
150
200
250
300
-0.06
T (K)
„
„
‹
„
„
„
‹
TEM analysis - 7 nm diameter
Magnetic fitting
Diameter
6.2 + 0.5 nm
‹ K
7.0x105 + 3.5x105 ergs cm-3
Smaller “magnetic” diameter accounted for by the presence of oxide layer.
Anisotropy close to bulk fcc value
Remnant magnetization is half saturation magnetization at low temperatures
Implies uniaxial symmetry
‹ Predicted for MT polyhedra
10000
H (G)
Magnetic modeling of ε-Co nanoparticles
0.004
M (emu)
Saturation Magnetization (1 Tesla)
0.003
M (emu)
(0.1 Tesla)
0.004
0.002
Expt.
Fit
0.002
0.000
-10000
0.001
Remnant magnetization (120 s)
-5000
0
5000
-0.002
0.000
0
50
100
150
200
250
300
-0.004
T (K)
•
•
TEM analysis - diameter of 9.5 nm
Magnetic fitting
–
–
•
•
Diameter 8.4 + 0.9 nm
Anisotropy 7.1x105 + 4.0x105 ergs cm-3
Anisotropy also close to bulk fcc value
Remnant magnetization is half saturation magnetization at low temperatures
–
Implies uniaxial symmetry.
10000
H (G)
Materials Selection: KuV >> kT
Ku
103
Ni
NiO.Fe2O3
Fe
104
105
106
107
108
109
Cubic
KuV >> kT
KuV < kT
CoOFe2O3
BaO.6Fe2O3
Co
MnAl
CoPt
FePt
Fe14Nd2B
YCo5
SmCo5
SmFe11Ti
Hexagonal
Tetragonal
Hard
magnets
Crystal Anisotropy
Shape Anisotropy
Exchange Anisotropy
Strain Anisotropy
Co
Pt
CoPt L10 structure
(tetragonal)
Shape ?
Solution phase synthesis
Example: FePt nanopartilces
Starting Materials
Mixing
Particle dispersion
FeCl2
FePt
FePt
FePt
Pt(acac)2
FePt
FePt
COOH (acid)
FePt
FePt
FePt
NH2 (amine)
FePt
LiBEt3H (Superhydride )
200-260°C
H 3C
CH 3
O
O
Pt(acac)2 =
Pt
O
H 3C
O
CH 3
S. Sun, C. B. Murray,
IBM Yorktown
Nanoparticles for magnetic storage
• Narrow size distribution
higher thermal stability
• Smaller particles
narrower transition widths
35 GBit/in2 prototype media
8.5 nm grains
σarea ≅ 0.6
50 nm
Nanoparticle arrays
4 nm FePt particles
σarea ≅ 0.05
50 nm
S. Sun, Ch.Murray, D. Weller, L. Folks, A. Moser, Science, 287 (2000) 1989
Magnetic properties
• Annealing leads to formation of ordered,
ferromagnetic phase
Chemically
disordered
fcc structure
Superparamagnetic
Annealing at 550C
Pt
Chemically
ordered
fct structure
Ferromagnetic
Fe
C axis
Magnetic properties
• Order parameter and coercivity increase with
annealing temperature and duration
3 layer samples of 6 nm FePt particles
1
0
-100
-200
580 ºC
650 ºC
400 ºC
450 ºC
-300
-20-15-10 -5 0 5 10 15 20
H (kOe)
Order parameter
200
100
20
0.8
N2
0.6
15
N2
10
0.4
FG
5
0.2
FG
0
0
30 0 40 0 500 60 0 700 80 0 90 0
tempe ratu re (C )
XRD data M. Toney, IBM Almaden
Hc (kOe)
M (emu/cm3)
300
VSM Hysteresis loops
3 layers, annealed in N2 at 580 C for 30 min, FePt samples from FeCl2
0.15
perpendicular
parallel
moment (memu)
0.1
“3D” random
assembly of 4nm
particles
0.05
0
-0.05
-0.1
-0.15
-20
-15
-10
-5
0
5
10
magnetic field (kOe)
15
20
Chemical analysis
12
20% Fe
80% γ Fe2O3
8
4
Unannealed
Hc = 0
0
700 705 710 715 720 725 730
energy (eV)
Total electron yield (rel. units)
Total electron yield (rel. units)
• Near Edge X-ray Absorption Fine Structure (NEXAFS)
spectroscopy shows iron oxide fraction that is reduced upon
annealing
• NEXAFS more sensitive to particle surface
- averaged ratio may be
16
16
different
12
60% Fe
40% γ Fe2O3
8
4
650 oC 5 min,
Hc = 8.4 kOe
0
700 705 710 715 720 725 730
energy (eV)
Special thanks to Robin Farrow for providing iron oxide reference samples.
Structural properties
a
c
b
50 nm
1
20
0.8
15
0.6
10
0.4
5
0.2
0
0
0
400
800
o
50 nm
(111) coherence length (nm)
Fraction of L10 pahse
50 nm
TEM images of 6 nm
particles
(a) as synthesized
(b) 530 ºC for 60 min
in vacuum
(c) 600 ºC for 60 min
in vacuum
TEM images courtesy of Zu-Rong Dai
• X-ray scattering and
TEM used to study
structural properties
3 layers of 4 nm particles annealed in N2
tem perature ( C)
XRD data M. Toney, IBM Almaden
Polymer-mediated self assembly
•
Substrate surface is functionalized
•
Dipped into dispersion of stabilized
nanoparticles
•
Ligand exchange leads to formation of
strongly bound layer of nanoparticles
•
New layer of functional molecule replaces
stabilizer
Substrate
•
Repeat process to form multilayers
Substrate
Functional polymer
Substrate
Substrate
S. Sun, C. B. Murray, IBM Yorktown
Magnetic recording
Computer
V
Servo
Electronics
I
4 nm ferromagnetic
FePt particle assembly
Writing
>
Slider
Sample
> X-Y Piezo Scanning Stage
to piezos
Reading
500 fc/mm
4
2
0
1040 fc/mm
MR signal [mV]
-2
-4
-6
2140 fc/mm
-8
-1 0
5000 fc/mm
-1 2
-1 4
-1 6
-1 8
-2 0
0
5
10
15
x [µ m ]
20
25
Size control of nanocrystals in the absence of Ostwald ripening
p
r
e
c
u
r
s
o
r
s
nucleation
growth
Factors influencing the nucleation rate
fast
until all monomer is
consumed
slow
CoPt3 nanocrystals
220 oC
170 oC
200 oC
145 oC
• reaction temperature
• concentrations of precursors
• concentrations of surfactants
Fe2O3 nanocrystals
307 oC
255 oC
245 oC
200 oC
Cobalt Nanocrystal Superlattices (T. Betley et al)
Hexagonal packing
Cubic packing
10 nm Cobalt NCs
Three-dimensional colloidal supercrystals
of CoPt3 nanocrystals
Institute of Physical Chemistry, University of Hamburg,
Hamburg, Germany
hν
hν
vacuum
secondary electrons
sample surface
Electron
escape
depth 5 nm
Photon
penetration
depth
50 nm
sample
FePt
Fe2O3
polymer
3
2.5
2
FePt
1.5
Fe2O3
1
)
10
-6
0.5
Magnetisation (emu x10
contribution to spectrum (rel.
units)
For the unannealed particles the ratio in the spectra can be
estimated as 20%Fe, 80% Fe2O3 (I am still not sure what
oxide we have, maybe a mixture). On the left is the
contribution to the spectra as a function of radius. A 3nm
diameter FePt metal core with a 0.5nm thick oxide shell
would produce such a spectrum.
0
0
0.5
1
1.5
2
2.5
radius (nm)
20% Fe 80% gammaFe2O3
5
FePt 100201A-2 Perp2
Unannealed
Hc = 258 Oe
S = 0.10
0
-5
100201-A2
-10
14
-15
-10
12
-5
0
5
Applied Field (kOe)
10
15
10
15
10
10
Magnetisation (emu x10
-6
)
8
6
4
2
0
700
5
FePt 100201A-2 Inplane
Unannealed
Hc = 242 Oe
S = 0.14
0
-5
-10
705
710
715
720
725
730
735
-15
energy (eV)
-10
-5
0
5
Applied Field (kOe)
2
1.5
FePt
Fe2O3
1
For the annealed particles the metal ratio is much higher,
here an example for 650C/5min anneal. On the left is the
contribution to the spectra as a function of radius. A 3.6 nm
diameter FePt metal core with a 0.2nm thick oxide shell
would produce such a spectrum.
0.5
0
0.5
1
1.5
2
2.5
)
0
100
Magnetisation (emu x10
-6
contribution to spectrum (rel.
units)
2.5
radius (nm)
101701C
60% Fe 40% gammaFe2O3
FePt 101701C Perp2
Annealed 650/5 SS
Hc = 7847 Oe
S = 0.77
50
0
-50
-100
12
-10
10
100
-6
)
8
Magnetisation (emu x10
6
4
2
0
Applied Field (kOe)
10
FePt 101701C Inplane
Annealed 650/5 SS
Hc = 7115 Oe
S = 0.76
50
0
-50
-100
0
695
700
705
710
715
energy (eV)
720
725
730
735
-10
0
Applied Field (kOe)
10
FePt
gamm aF e2O3
F e3 O4
alpha F e2O3
FePt
gamm aF e2O3
F e3 O4
alpha F e2O3
0.7
2.5
(2)
0.6
2
(3)
0.5
1.5
(1)
0.4
1
(1)
0.3
0.5
0.2
0
718
0.1
720
7 22
724
ene rgy (eV)
L3
726
728
730
734
735
736
7 37
738
ene rgy (eV)
L2
739
740
741
742
lef t norm
right norm
F e3O 4 ru n 2012513
F e3O 4 ru n 2012513
0.2
6
0
5
-0.2
4
-0.4
3
-0.6
-0.8
2
-1
1
-1.2
0
715
720
725
730
735
740
-1.4
745
715
720
7 25
730
735
7 40
745
energy (e V)
ene rgy (e V)
Polar Kerr
H
Fe3O4
0.1
Kerr signal
Fe3O4 sample from Robin
XMCD in 500 Oe, 20 degrees incidence
along easy axis
run 20125013
0.05
0
-1000
-500
0
-0.05
-0.1
field (Oe)
500
1000
201240_20su m
Fe3O4 Rob in run 20124021
0.2
0.4
0
0.2
0
-0.2
-0.2
-0.4
-0.4
-0.6
-0.6
-0.8
-0.8
-1
-1
-1.2
-1.2
715
720
7 25
730
735
7 40
745
ene rgy (e V)
Fe3O4 sample from Robin
XMCD in 500 Oe, 20 degrees incidence
along easy axis
test reproducibility - is very good
715
720
7 25
730
ene rgy (e V)
735
7 40
745
Three layers of PEI-E066 on
Si(110) annealed under Ar +
H(5%) for 30 min. The samples
have been immersed into acetone
for 1 min and dried.
030902-A, 400C
030902-B, 450C
030902-C, 500C
030902-D, 530C
030902-E, 560C
030902-F, 580C
030902-A 400C Hc=0 Ms=115 emu/cm^3
400
M (emu/cm^3)
300
200
100
0
-20
030902-C 500C Hc=2.28 Ms=305 emu/cm^3
300
200
200
0
-200
20
M (emu/cm^3)
M (emu/cm^3)
300
10
100
0
-20
-10
-100
0
-200
-300
-300
-400
-400
H (kOe)
20
H (kOe)
400
0
10
-400
400
-100
0
-300
100
-10
-100
-200
030902-B 450C Hc=0.77 Ms=312 emu/cm^3
-20
-10
H (kOe)
10
20
And here the comparison between 8nm, 6nm, and 4nm.
0.06
4nm 5L
6 nm 7L
0.05
8nm 7L
0.04
0.03
0.02
0.01
0
700
705
710
7 15
720
en ergy (eV)
7 25
730
735
740
030902-E 560C Hc=2.7 kOe Ms=319 emu/cm^3
400
400
300
300
200
200
100
0
-20
-10
-100
0
10
20
-200
M (emu/cm^3)
M (emu/cm^3)
030902-D 530C Hc=2.3 kOe Ms=380 emu/cm^3
100
0
-20
-10
-100
0
10
20
-200
-300
-300
-400
-400
H (kOe)
H (kOe)
5
030902-F 580C Hc=4.8 kOe Ms=316 emu/cm^3
350
Ms
400
4
300
3
250
M (emu/cm^3)
300
200
100
Hc
0
-20
-10
-100
0
10
20
2
200
1
150
-200
-300
-400
H (kOe)
0
350
400
450
500
550
Anneal temperature (C)
100
600
0.5
0.4
0.3
0.2
0.1
0
350
400
450
500
550
Anneal temperature (°C)
From Mike Toney, XRD
600
12
10
8
6
4
2
0
350
400
450
500
550
Annealing temperature (°C)
From Mike Toney, XRD
600
30
B
Total electron yield (rel. units)
25
A
C
D
20
α− Fe O
2
γ − Fe O
15
2
Fe O
3
10
400°C
450°C
500°C
530°C
560°C
580°C
5
0
700
4
705
710
715
720
energy (eV)
725
Fe
730
3
3
Hello,
Here the data from the latest ALS run. Jan made two samples for comparison,
sample #4 is 50 nm Fe55Pt45 without cap layer
sample #5 is 50 nm Fe55Pt45 with 2 nm Pt cap layer
Here the Fe spectra for comparison. The one without cap layer is much more
oxidized as expected.
total yield (rel. units)
sample #4 FePt no cap
sample # 5 FePt with cap
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
700
4
5
710
720
730
energy (eV)
740
750
This graph shows sample #5 with respect to a clean Fe reference, and the best
fit to the spectrum I got with assuming 70% Fe and 30% FeO.
0.05
Fe
70%F e30% FeO
#5
0.04
0.03
0.02
0.01
0
700
705
710
715
720
energ y (eV)
7 25
730
735
740
And the contribution to the spectra of Fe and Fe3O4 for 8nm, 6nm, and 4nm.
If I put this into the model the oxide layer for the 6 and 8 nm particles seems
to be thinner (2A) than for the 4 nm particles (4A).
Fe f raction (% )
Fe3 O4 fra ction (% )
80
70
60
50
40
30
20
3
4
5
6
pa rticle size (nm)
7
8
9
-20
-10
0.12
0.1
0.08
0.06
0.04
0.02
0
-0.02 0
-0.04
-0.06
-0.08
-0.1
041801-F Hc=10.8 kOe
0.15
10
20
Polar Kerr angle (deg)
Polar Kerr angle (deg)
041801-E Hc=2.35 kOe
0.1
0.05
0
-20
-10
-0.05
0
10
-0.1
-0.15
H (kOe)
H (kOe)
6nm
8nm
The 8nm sample has very high coercivity.
041801-E
E098, 6nm
Fe52Pt48
SiO2/Si
PEI-E098,
7Layers
N2, 580C, 30 min
041801-F
E095, 8 nm
~Fe52Pt48
SiO2/Si
PEI-E095,
7Layers
N2, 580C, 30 min
20
This is a comparison of the films made 030101. They are all just after the onset
of being ferromagnetic, the spectra are all very similar.
4nm 3L F e50 Pt50 F e(C O)5
4nm 3L F e55 Pt45 F e(C O)5
8nm 1 L FeC l2
4nm 2 L Fe5 8Pt4 2 FeC l2
4nm 2 L Fe5 8Pt4 2 FeC l2
2.5
2
1.5
1
0.5
0
700
705
710
7 15
720
en ergy (eV)
725
730
735
740
030101-A Hc=1.2 kOe
0.01
0.005
0
-20
-10
-0.005 0
10
20
-0.01
-0.015
Polar Kerr angle (deg)
Polar Kerr angle (deg)
0.02
0.015
-20
-10
-0.02
H (kOe)
0.01
0.005
0
10
20
-0.01
-0.015
Polar Kerr angle (deg)
Polar Kerr angle (deg)
0.02
-0.005 0
20
-20
-10
0.01
0.008
0.006
0.004
0.002
0
-0.002 0
-0.004
-0.006
-0.008
-0.01
H (kOe)
030101-D Hc=1.2 kOe
0.015
-10
10
H (kOe)
030101-B Hc=2.4 kOe
-20
0.025
0.02
0.015
0.01
0.005
0
-0.005 0
-0.01
-0.015
-0.02
-0.025
Hc=1.1 kOe
Polar Kerr angle (deg)
030101-C Hc=0.14 kOe
-20
-0.02
H (kOe)
-10
0.025
0.02
0.015
0.01
0.005
0
-0.005 0
-0.01
-0.015
-0.02
-0.025
10
20
H (kOe)
030101-A
E066, Fe58Pt42
SiO2/Si
PEI-Fe58Pt42, 2 layer
N2, 580C, 30 min
030101-B
E066, Fe58Pt42
SiO2/Si
PEI-Fe58Pt42, 2 layer
N2, 580C, 30 min
030101-C
F062, Fe50Pt50
SiO2/Si
PEI-Fe50Pt50, 3 layers
N2, 580C, 30 min
030101-D
F070, Fe55Pt45
SiO2/Si
PEI-Fe55Pt45, 3 layers
N2, 580C, 30 min
030101-E
E068,
~8nm FePt
SiO2/Si
PEI-FePt, 1 layer
N2, 580C, 30 min
10
20
Hi all,
I did a calculation of the signal one would expect in total yield detection for the following
geometry:
This is basically a particle of 40A diameter with 32A FePt core surrounded by one monolayer
Fe3O4. It is embedded in the polymer (for the calculation I assumed just carbon) with 60A
particle distance, that gives about 10A carbon on top.
polymer
Fe3O4
FePt
32A
40A
10A
Fe3O4 Nanocrystals
(Sun and Zeng)
Fe(acac)2
or
Fe(acac)3
TOE or DOE
OA (and tributylphosphine)
300 C
TOA or DOE
OA, 350 C
armorphous
Fe-NC
Fe(CO)5
TOA, OA
300 C
N O
Ox
in
air
FeO
>300 C
Fe + Fe3O4
Shape selective synthesis of wuestite
Substitute
trimetylamine N-oxide
with pyridin N-oxide
Fe(CO)5
oleic acid
dioctyl ether
or trioctylamine
∆T
FeO-NC
N O
FeO Nanoparticles
Right a) TEM image of a single cubic superlattice built of cubic FeO nanocrystals with 11 nm edge length. b) TEM image of a
larger superlattice oxidized or decomposed after storage. c) SAED of the cubic superlattice in b) showing reflections for magnetite
and orientational ordering in the superlattice.
Right: a) LRTEM image of a quadratic subunit of a TEM grid showing nearly cubic superlattice built up of cubic wuestite nanocrystals.
b) SAED of a selected superlattice with uneven but symmetric intensity distribution caused by preferred alignment of the particles
(orientational ordering). c) TEM image of aligned superlattices arising during deposition of cubic FeO nanocrystals in a magnetic field
parallel to the substrate. d) TEM image of aggregated superlattices deposited without external magnetic field.
Figure 6: a) TEM image of wuestite nanocrystals with seeds of magnetite inside. b) SAED of the material showing a speckled pattern for FeO
reflections and diffuse rings for magnetite reflctions. c) Dark-field image of the region in Figure 5a (shown as negative); a part of the magnetite
reflections were selected with the objective aperture. d) Dark-field image of the region in Figure 5a (shown as negative); a part of the wuestite
reflections were selected with the objective aperture.
Fe3O4 nanoparticles
Sun et al, J. Am. Chem. Soc. 2004, 126, 273.
Shape induce crystal alignment
(14 nm MnFe2O4 nanoparticles)
(100) texture
(400)
16000
14000
Y Axis Title
12000
10000
8000
6000
4000
2000
(220) (311)
20
30
40
(511) (440)
50
60
70
80
2θ
(100) texture
H. Zeng, et al
Dark Field Imaging of the Fe3O4 and FeO in TEM.
Figure 6: a) TEM image of wuestite nanocrystals with seeds of magnetite inside. b) SAED of the material showing a speckled pattern for FeO
reflections and diffuse rings for magnetite reflctions. c) Dark-field image of the region in Figure 5a (shown as negative); a part of the magnetite
reflections were selected with the objective aperture. d) Dark-field image of the region in Figure 5a (shown as negative); a part of the wuestite
reflections were selected with the objective aperture.
Bimagnetic Core/Shell Nanoparticles
Zeng et al, Nano Lett. 2004, 4, 187.
Spin-dependent tunneling in Nanocrystal arrays
Chuck Black, Bob Sandstrom, Chris Murray, Shouheng Sun
I (pA)
400
T = 70 K
T=2K
200
0
-200
-400
-0.4
shortest current path ~ 8 nanocrystals
-0.2
0.0
V (V)
0.2
0.4
10
2
10
1
10
0
10
-1
10
-2
10
-3
1.00
20
40
60
80x10
-3
-1
1/T (K )
data fit by:
ln(GV=0) = const. - Ec/kBT
from fit to data, measure EC~ 10 meV
for all devices measured, 10 meV < EC < 14 meV
R/RH=0
GV=0 (1/GΩ)
GV=0 follows simple thermal-activation
H
H
0.98
0.96
0.94
0.92
-0.4
-0.2
0.0
0.2
applied field (T)
0.4
Fe3O4 Nanocrystals
(Sun and Zeng)
20
70 K
15
80 K
H =0
H = 3.5 T
10
I (nA)
90 K
5
0
-5
-10
-4
-3
-2
-1
0
1
2
3
140 K
-15
110 K
100
-20
-0.4
4
-0.2
0.0
0.2
0.4
VB (V)
H (T)
-0.26
-0.25
-0.28
-0.26
-0.27
-0.30
-0.28
MR
MR
(R(H)-R(0))/R(0) (%)
2
0
-2
-4
-6
-8
-10
-12
-14
-16
-18
-20
-0.32
-0.29
60 K
-0.34
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
Vb
-0.30
100 K
-0.31
-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4
Vb
Potential for spintronic device applications
Nanoparticle synthesis from
self-assembled polymer templates
• Diblock
copolymer
system
PS/PMMA
• Self-assembly
promoted by
heating
• Removal of
PMMA
100
nm
metallization
remove polymer
C.
Black, K.
W. Guarini, R. L. Sandstrom, IBM Yorktown
• T.Metal
deposition