On 23rd January 2018 at 14:00 Dr Andrew Carauna will give a physics seminar in room INB3305. Below is the title, abstract and summary of Andrew’s work.
Title:
Studying the spin Seebeck Effect using Polarised Neutron Reflectivity
Talk outline:
Thermoelectric generators (TEGs) are of increasing interest due to their potential use in energy harvesting of waste heat. The efficiency of such devices is often characterised by the thermoelectric figure of merit, zT[1], which is ultimately limited by the thermal and electric conductivities in conventional TEGs. The ideal TEG material should have a high electrical conductivity (to reduce resistive losses), and low thermal conductivity (so that a large temperature gradient can be setup across the device) for the optimisation of zT. However, these properties are intrinsically linked to one another, as best described by the Weidemann-Franz Law (κ=σL0T), thus providing a limit to the upper value of zT.
The spin Seebeck effect (SSE) may overcome this limitation. When a thermal gradient is applied to a magnetised ferromagnet (FM) it can induce a spin current, JS [2]. By placing a heavy metal (NM) in contact with a FM material, JS can be converted to a charge current, JC, via the inverse spin hall effect (ISHE). Due to the separation of the active material (FM layer) and the electric circuit (NM layer) the FM layer can be chosen so that the thermal conductivity is minimised without affecting the electrical conductivity of the contact NM layer.
Polarised Neutron Reflectivity (PNR) provides information of the physical density and magnetic moment of a thin film or multilayer as a function of depth. Since PNR can probe buried interfaces, layer and interface parameters such as layer thickness, layer density, magnetic moment of the layer and the roughness at each interface can be determined. By the use of specific sample environment (magnets, cryostats, furnaces etc.), the depth profile of the magnetic moment can be probed under a variety of different conditions. In our recent work we have been investigating the magnetic depth profile of our SSE based devices[2] when a thermal gradient is applied across the device, using a custom built thermal cell. In this talk, I will provide an introduction to the SSE, PNR and the POLREF beamline at ISIS and show our recent work using the in-situ SSE-thermal cell.
[1] L. E. Bell, Science, 321, 1457 (2008)
[2] K. Uchida et al, J. Phys. Condens. Matter, 26, 343202 (2014)
[3] A. Caruana et al, Phys. Status Solidi RRL 10, No. 8, 613–617 (2016)
About Dr Andrew Carauna:
Studied for an undergraduate masters MPhys in pure physics at Loughborough University (graduated 2010). Conducted an experimental PhD in physics on pulsed laser deposition (PLD) of oxide thin films (graduated 2015, Supervisor Dr Mike Cropper). I was a postdoc for 1 year working under Dr Kelly Morrison on the Spin Seebeck Effect (SSE), growing thin film SSE devices using PLD. I now work as an instrument scientist on the POLREF polarised neutron reflectometer at the ISIS Neutron and Muon Source. My main research interests lie in magnetic thin film devices for use in spintronics, i.e. the Spin Seebeck effect, specifically looking at interfacial effects on the induced spin pumping within these devices. Additionally, I am also interested in developing sample environment for in-situ measurement techniques on the beamline, i.e. in-situ SSE and ferromagnetic resonance/spin pumping.
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