New Directions in Energy Research or a Magnetic Quirk?

Report
New Directions in
Energy Research or a
Magnetic Quirk?
Research Interests
Superconductors
Magnetocaloric Effect
Thermoelectric effect
Waste heat
harvesting
Magnetic
refrigeration
Low loss power
transfer
http://www.superconductors.org/INdex.htm
Superconductivity
Courtesy Dr Gaifullin
Zero Resistance
Magnetic Levitation
Applications:
MRIs
CERN
Superconductors at CERN
2008: Magnets
quenched at the
LHC (CERN),
putting back
discovery of the
‘Higgs boson’ by
approximately a
year.
http://youtu.be/BEnaEMMAO_s
http://press.web.cern.ch/press-releases/2008/10/cern-releases-analysis-lhc-incident
Magnetocaloric Effect
(Solid State Magnetic Refrigeration)
http://www.sseec.eu/Solid_State_Energy_Efficient_Cooling.html
Magnetocaloric Effect
(Solid State Magnetic Refrigeration)
Need to find the
right material…
http://www.sseec.eu/Solid_State_Energy_Efficient_Cooling.html
The Thermoelectric Effect

=

JQ = Π
JQ
JC
Π = 
Onsager Reciprocity
• Onsager-Thomson:  = 
• Onsager reciprocity: Lij=Lji
•
•
•
•
•
•
•

11
 = 12
21
22
∆
−∆

∆

 
=Peltier coefficient
 =   −∆
S=Seebeck coefficient
∆

=
K=Thermal conductivity
∆ =0
Spin dependant
R=1/σ=electrical resistance=1/σ

Seebeck effect
= 
∆=0
Jc = charge current
( ↓ + ↑)/2
1



Lars
Chemistry

1the Nobel
′  prize
 Onsager
(for
↓ −
↑)/2
= ( ) received
JQ = heat current
in 1968 "for the
discovery
the reciprocal
relations
′  ofκ/
−/

bearing his name, which are fundamental for the
Js = spin current
 −
thermodynamics of irreversible processes“


Spin dependant
Peltier effect
=


()
′ =


↑
↓
Harvesting Heat
NASA Mars Rover
Powered by
plutonium238
http://mars.jpl.nasa.gov/files/mep/MMRTG_Jan2008.pdf
Peltier Cells to Recover Waste Heat
Skudderites are
a popular TEG
material:
Limited Thermoelectric Efficiency?
• Cost
• Efficiency
• Figure of merit
2
 =

• Wiedeman Franz Law
0
 = 0 =

2 
0 =
3 
2
=2.44 x 10−8 W Ω K−2
http://www1.eere.energy.gov/vehiclesandfuels/pdfs/deer_2004 /session4/2004_deer_fairbanks2.pdf
Current State of the Art
κ = κ + κ
Vineis et al., Adv. Mater., 22, 3970-3980 (2010)
Nanostructuring or bulk
engineering to improve ZT
K. Biswas et al., Nature, 489, 414-418 (2009)
The Spin Seebeck Effect
Co2MnSi
NiFe
GaMnAs
YIG
LaY2Fe5O12
K. Uchida et al., Nature Letters, 455, 778-781 (2008)
Onsager Reciprocity
• Onsager-Thomson:  = 
• Onsager reciprocity: Lij=Lji
•
•
•
•
•
•
•

11
 = 12
21
22
∆
−∆

∆

 
=Peltier coefficient
 =   −∆
S=Seebeck coefficient
K=Thermal conductivity
Spin dependant
R=1/σ=electrical resistance=1/σ
Seebeck effect
Jc = charge current
( ↓ + ↑)/2
1



1
′ 
 = ( ) 
( ↓ − ↑)/2
JQ = heat current
 ′  κ/

−/
Js = spin current
 −
Spin dependant
Peltier effect
=


()
′ =


↑
↓
2007 Nobel Prize: Fert and Grϋnberg
(GMR)
Giant Magneto Resistance
(GMR) achieved by thin films
magnetised anti-parallel (with
respect to each other).
Moore’s Law
“Number of transistors doubles every 2 years”
“Data storage density doubles every 2 years”
“Processing power doubles every 2 years”
GMR
Intel Corp.
http://www.mooreslaw.org/
What Exactly is Spintronics?
Giant MR
Andreev Reflection
Spin Hall effect in
PMs
Current induced spin
polarisation in PMs
Using charge
and spin to
contain
information:
Four possible
states (qubits).
D. Pesin and A.H. MacDonald, Nature Materials, 11, 409-416 (2012)
The Spin Seebeck Effect
Transverse spin Seebeck
Longitudinal spin Seebeck
VISHE
VISHE
B
T
T
Material
Spin
Current
Charge
Current
Normal metal


Ferromagnetic metal


Ferromagnetic
semiconductor


Ferromagnetic
insulator


A spin current may flow in
an electric insulator
Aside: How do You Detect a Spin
Current?
Spin Hall Effect: Generation of a spin polarised current due to
charge current flowing from a paramagnet to a ferromagnet.
Inverse Spin Hall Effect: Generation of a voltage – EISHE – due
to a spin polarised current.
Heavy metals such as Pt
are typically very good
for detection of Js by
generation of EISHE.
Aside: Spin Hall Angle
Can be thought of as the
efficiency with which a
spin current, JS is
converted to a charger
current, JC.


=

Element
Spin Hall
Angle, θSH (%)
Al
0.02
Au
0.25 — 11
Bi
>0.8
Cu
0.22
Mo
-0.05 — -0.8
Nb
-0.87
Pd
0.64 — 1
Pt
1.3 — 11
Ta
-0.37 — -12
W
-33
Maximising VISHE, Minimising Cost
Contact
Cost of host metal
($/g)
Cost of dopant
($/g)
Total cost of contact
($/g)
Measured (M), or predicted (P),
spin Hall angle (%)
Pt
50.95
-
50.95
Cu
0.12
-
0.12
Cu+1% Pt
0.12
51
0.63
1.2 to 11[1]
(M)
0.22 [2]
(M)
2.7 [3]
(P)
Cu+1% Bi
0.12
0.02
0.12
8.1 [3]
(P)
Cu+1% Ta
0.12
6.3
0.18
-1 [4]
(P)
Ag
0.71
-
0.71
Ag+1% Pt
0.71
51
1.21
0.47 [2]
(M)
1.0 [3]
(P)
Ag+1% Bi
0.71
0.02
0.7
[1] A. Hoffman, IEEE Trans. Magn., 49, 5172 (2013).
[2] H.L. Wang et al., arXiv:1307.2648 (2013).
[3] M. Gradhand et al., Phys. Rev. B, 81 245109 (2010).
[4] A. Fert and P.M. Levy, Phys. Rev. Lett., 106 157208 (2011).
1.4 [3]
(P)
Measuring the Spin Seebeck Voltage
B
The Next Stage?
Impact of the Spin Seebeck Effect
Energy
Materials for energy
applications
Energy
efficiency
Energy
storage
Thermoelectrics
Increased
figure of merit,
ZT
Reduced
fabrication
costs
Information and
Communication Thermal spin
Technologies transfer torque
Non-CMOS
technology
Charge
transport
Spin
transport
Thermal
transport
Spintronics
Spin
valves
Quantum
Computing
Physical
Sciences
Tunnel
Magnetic heat junctions
switches
Available PhD project.
“As part of the PhD you will be expected to characterise potential spin Seebeck
samples using x-ray diffraction, x-ray reflectivity, transport measurements,
thermal transport and magnetometry. It is also likely that you will prepare
patterned thin films using pulsed laser deposition and physical vapour deposition
techniques.”
http://homepages.lboro.ac.uk/~phkm2/Phd.htm
Pieter Kok (Sheffield) on Quantum Imaging
Dan Browne (UCL) on D-Wave’s “quantum”
computer
When: 7pm Wed 26 March
Where: Swan in the Rushes (upstairs)
Target Audience: Part C and above but all
welcome
(space permitting)

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