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Slide 1
New Directions in Energy Research or a Magnetic Quirk?
Slide 2
Superconductors Magnetocaloric Effect Thermoelectric effect
Superconductors Magnetocaloric Effect Thermoelectric effect
Research Interests http://www.superconductors.org/INdex.htm Waste
heat harvesting Low loss power transfer Magnetic refrigeration
Slide 3
Superconductivity Zero Resistance Magnetic Levitation
Applications: MRIs CERN Courtesy Dr Gaifullin
Slide 4
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
Slide 5
Magnetocaloric Effect (Solid State Magnetic Refrigeration)
http://www.sseec.eu/Solid_State_Energy_Efficient_Cooling.html
Slide 6
Magnetocaloric Effect (Solid State Magnetic Refrigeration) Need
to find the right material
http://www.sseec.eu/Solid_State_Energy_Efficient_Cooling.html
Slide 7
The Thermoelectric Effect JCJC JCJC JQJQ
Slide 8
Onsager Reciprocity Spin dependant Seebeck effect Spin
dependant Peltier effect Lars Onsager received the Nobel prize for
Chemistry in 1968 "for the discovery of the reciprocal relations
bearing his name, which are fundamental for the thermodynamics of
irreversible processes
Slide 9
Harvesting Heat Powered by plutonium- 238
http://mars.jpl.nasa.gov/files/mep/MMRTG_Jan2008.pdf NASA Mars
Rover
Slide 10
Peltier Cells to Recover Waste Heat Skudderites are a popular
TEG material:
Slide 11
Limited Thermoelectric Efficiency? Cost Efficiency Figure of
merit Wiedeman Franz Law
http://www1.eere.energy.gov/vehiclesandfuels/pdfs/deer_2004
/session4/2004_deer_fairbanks2.pdf
Slide 12
Slide 13
Current State of the Art K. Biswas et al., Nature, 489, 414-418
(2009) Nanostructuring or bulk engineering to improve ZT Vineis et
al., Adv. Mater., 22, 3970-3980 (2010)
Slide 14
The Spin Seebeck Effect Co 2 MnSi NiFe GaMnAs YIG LaY 2 Fe 5 O
12 K. Uchida et al., Nature Letters, 455, 778-781 (2008)
2007 Nobel Prize: Fert and Grnberg (GMR) Giant Magneto
Resistance (GMR) achieved by thin films magnetised anti-parallel
(with respect to each other).
Slide 17
Moores Law http://www.mooreslaw.org/ Intel Corp. Number of
transistors doubles every 2 years Data storage density doubles
every 2 years Processing power doubles every 2 years GMR
Slide 18
What Exactly is Spintronics? Using charge and spin to contain
information: Four possible states (qubits). D. Pesin and A.H.
MacDonald, Nature Materials, 11, 409-416 (2012) Giant MR Andreev
Reflection Current induced spin polarisation in PMs Spin Hall
effect in PMs
Slide 19
The Spin Seebeck Effect B V ISHE TT MaterialSpin Current Charge
Current Normal metal Ferromagnetic metal Ferromagnetic
semiconductor Ferromagnetic insulator V ISHE TT Transverse spin
SeebeckLongitudinal spin Seebeck A spin current may flow in an
electric insulator
Slide 20
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 E ISHE due to a spin polarised
current. Heavy metals such as Pt are typically very good for
detection of J s by generation of E ISHE.
Slide 21
Can be thought of as the efficiency with which a spin current,
J S is converted to a charger current, J C. Aside: Spin Hall Angle
ElementSpin Hall Angle, SH (%) Al0.02 Au0.25 11 Bi>0.8 Cu0.22
Mo-0.05 -0.8 Nb-0.87 Pd0.64 1 Pt1.3 11 Ta-0.37 -12 W-33
Slide 22
Maximising V ISHE, 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 (%) Pt50.95- 1.2 to 11[1]
(M) Cu0.12- 0.22 [2] (M) Cu+1% Pt0.12510.63 2.7 [3] (P) Cu+1%
Bi0.120.020.12 8.1 [3] (P) Cu+1% Ta0.126.30.18 -1 [4] (P) Ag0.71-
0.47 [2] (M) Ag+1% Pt0.71511.21 1.0 [3] (P) Ag+1% Bi0.710.020.71.4
[3] (P) [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).
Slide 23
Measuring the Spin Seebeck Voltage B
Slide 24
The Next Stage?
Slide 25
Impact of the Spin Seebeck Effect Thermal transport Spin
transport Charge transport Reduced fabrication costs Spintronics
Spin valves Magnetic heat switches Tunnel junctions Quantum
Computing Physical Sciences Increased figure of merit, ZT
Thermoelectrics Energy Energy efficiency Energy storage Materials
for energy applications Information and Communication Technologies
Thermal spin transfer torque Non-CMOS technology
Slide 26
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