New Directions in Energy Research or a Magnetic Quirk?

Superconductors Magnetocaloric Effect Thermoelectric effect Superconductors Magnetocaloric Effect Thermoelectric effect Research Interests Waste heat harvesting Low loss power transfer Magnetic refrigeration

Superconductivity Zero Resistance Magnetic Levitation Applications: MRIs CERN Courtesy Dr Gaifullin

Superconductors at CERN 2008: Magnets quenched at the LHC (CERN), putting back discovery of the ‘Higgs boson’ by approximately a year.

Magnetocaloric Effect (Solid State Magnetic Refrigeration)

Magnetocaloric Effect (Solid State Magnetic Refrigeration) Need to find the right material…

The Thermoelectric Effect JCJC JCJC JQJQ

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“

Harvesting Heat Powered by plutonium NASA Mars Rover

Peltier Cells to Recover Waste Heat Skudderites are a popular TEG material:

Limited Thermoelectric Efficiency? Cost Efficiency Figure of merit Wiedeman Franz Law /session4/2004_deer_fairbanks2.pdf

Current State of the Art K. Biswas et al., Nature, 489, (2009) Nanostructuring or bulk engineering to improve ZT Vineis et al., Adv. Mater., 22, (2010)

The Spin Seebeck Effect Co 2 MnSi NiFe GaMnAs YIG LaY 2 Fe 5 O 12 K. Uchida et al., Nature Letters, 455, (2008)

Onsager Reciprocity Spin dependant Seebeck effect 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 Intel Corp. “Number of transistors doubles every 2 years”  “Data storage density doubles every 2 years”  “Processing power doubles every 2 years” GMR

What Exactly is Spintronics? Using charge and spin to contain information: Four possible states (qubits). D. Pesin and A.H. MacDonald, Nature Materials, 11, (2012) Giant MR Andreev Reflection Current induced spin polarisation in PMs Spin Hall effect in PMs

The Spin Seebeck Effect B V ISHE TT MaterialSpin Current Charge Current Normal metal  Ferromagnetic metal Ferromagnetic semiconductor  Ferromagnetic insulator  V ISHE TT Transverse spin SeebeckLongitudinal spin Seebeck 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 – 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.

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, θ 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

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 (%) Pt to 11[1] (M) Cu [2] (M) Cu+1% Pt [3] (P) Cu+1% Bi [3] (P) Cu+1% Ta [4] (P) Ag [2] (M) Ag+1% Pt [3] (P) Ag+1% Bi [3] (P) [1] A. Hoffman, IEEE Trans. Magn., 49, 5172 (2013). [2] H.L. Wang et al., arXiv: (2013). [3] M. Gradhand et al., Phys. Rev. B, (2010). [4] A. Fert and P.M. Levy, Phys. Rev. Lett., (2011).

Measuring the Spin Seebeck Voltage B

The Next Stage?

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

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.”