New Directions in Energy Research or a Magnetic Quirk?
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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 ππ π= ππ JQ = Ππ½π JQ JC Π = ππ Onsager Reciprocity • Onsager-Thomson: π« = ππ • Onsager reciprocity: Lij=Lji • • • • • • • π½π πΏ11 π½π = πΏ12 πΏ21 πΏ22 βπ −βπ π βπ π½π π π π«=Peltier coefficient π½π = π« πΎ −βπ S=Seebeck coefficient βπ π = K=Thermal conductivity βπ π½π=0 Spin dependant R=1/σ=electrical resistance=1/σ π½ Seebeck effect π«= π½ βπ=0 Jc = charge current π»(π ↓ +π ↑)/2π 1 π ππ π½π Lars Chemistry π 1the Nobel π′ ππ prize π½π Onsager π»(πfor ↓ −π ↑)/2π = π(ππΉ ) received JQ = heat current in π½1968 "for theππ discovery the reciprocal relations π′ ππ ofκπ/π −π»π/π π bearing his name, which are fundamental for the Js = spin current π −π thermodynamics of irreversible processes“ π π Spin dependant Peltier effect π= ππΉ π π(ππ) π′ = ππΉ ππ ↑ ↓ 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 π2π ππ = π ο« • Wiedeman Franz Law πΏ0π ο« = ππΏ0π = π π2 ππ΅ πΏ0 = 3 π 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 = κππ + κπππ‘ 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: π« = ππ • Onsager reciprocity: Lij=Lji • • • • • • • π½π πΏ11 π½π = πΏ12 πΏ21 πΏ22 βπ −βπ π βπ π½π π π π«=Peltier coefficient π½π = π« πΎ −βπ S=Seebeck coefficient K=Thermal conductivity Spin dependant R=1/σ=electrical resistance=1/σ Seebeck effect Jc = charge current π»(π ↓ +π ↑)/2π 1 π ππ π½π 1 π′ ππ π½π = π(ππΉ ) π π»(π ↓ −π ↑)/2π JQ = heat current ππ π′ ππ κπ/π π½π −π»π/π Js = spin current π −π Spin dependant Peltier effect π= ππΉ π π(ππ) π′ = ππΉ ππ ↑ ↓ 2007 Nobel Prize: Fert and GrΟnberg (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” 﨓Data storage density doubles every 2 years” 﨓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 ο³T ο³T Material Spin Current Charge Current Normal metal ο» οΌ Ferromagnetic metal οΌ οΌ Ferromagnetic semiconductor οΌο» οΌο» Ferromagnetic insulator οΌ ο» 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. πππ» π±π = π±π 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)
