A new window on caloric effects in spin transport With Moore’s law expected to break down in the relatively near future, researchers are searching for new ways to control heat, charge and spin currents in nanostructures. The SpinCaT priority programme supports research into novel spin caloric effects, which could lead to interesting new functionalities, as Professor Christian Back explains It is expected that Moore’s law will break down with respect to CMOS technologies in the relatively near future due to the thermodynamic bottleneck, prompting a renewed focus on research into thermodynamic transport, spin caloric effects and other related topics. With circuit designers approaching physical limits in terms of the number of components that will fit on an integrated circuit, scientists are searching for new ways to control heat, charge and spin currents in nanostructures, topics central to the work of the SpinCaT priority programme. “The aim of SpinCaT was to develop the new research field of caloric effects in spin transport,” explains Professor Christian Back, the programme’s coordinator. Over 40 projects were supported under the programme, focussing on four areas. “These were spin caloric effects and spin mediated heat transport in planar geometry, thermal conductivities across interfaces in nanopatterned devices, spin currents induced by large temperature gradients and materials for spin caloric applications,” outlines Professor Back.
system FeCo, which allowed us to systematically tune the Fermi energy through the band structure, and to investigate the evolution of the transport properties with respect to composition.” A number of projects within the programme have focused on other novel spin-caloric effects, the spin counterparts of well-known thermoelectric effects like the Peltier effect. A deeper understanding of the electronic band structure
We have established an experimental platform for the simultaneous measurement of the electric, thermoelectric and thermal transport coefficients of metal films. The platform was applied to the alloy system FeCo, which allowed us to systematically tune the Fermi energy Spin caloric effects The projects were selected for inclusion in the programme solely according to scientific value, with scientists looking to build a deeper understanding of novel spin caloric effects, which can modify thermal transport, magneto-resistance and possibly even magnetic states. Based himself at the Technical University of Munich, Professor Back has been working on a project looking at the spin-dependent Seebeck effect, as well as thermal spin transfer torque. “We have clarified inconsistent evidence from different experiments in the literature, by showing that the so-called transversal spin-Seebeck effect in metals is unobservably small, when compared to the competing (established) magnetothermoelectric effects,” he outlines. “In the course of these efforts, we have established an experimental platform for the simultaneous measurement of the electric, thermoelectric and thermal transport coefficients of metal films. The platform was applied to the alloy
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and electron transport can help researchers to optimize these effects. “A good example is the design of materials in Ferromagnetic alloy/tunnel junction/ferromagnetic alloy elements based on e.g. Fe/MgO/Fe, where the spin dependent Seebeck effect can be optimized by tuning the electronic band structure and thus improving electron transport across such a device,” says Professor Back. Research within the programme holds a lot of interest for industry, for example with respect to harvesting energy from waste heat using spintronic materials, while Professor Back says there are also other examples. “Heat management in nanoscale spintronic devices, such as read sensors or nano-oscillators, is another area of interest for industry. Then there’s energy harvesting in wearable electronics, employing the spin Seebeck effect,” he outlines. The primary motivation in research is scientific interest however, rather than the possibility of commercial applications, and the focus now is
building on the progress that has been made. Professor Back and his colleagues are applying a lot of technical advances that were achieved within their project, using spin Hall effects as efficient detection and characterization techniques, yet the focus of their research has shifted. “We are working on skyrmion hosting materials, as a new priority programme has just started on this topic. Skyrmions are non collinear magnetic nanosized topological objects that can be controlled and manipulated by spin currents and hold a lot of potential for future magnetic storage devices,” says Professor Back.
SPINCAT PP 1538 Spin Caloric Transport The priority programme was funded by the DFG for six years with a total amount of about 12 Million Euros. Professor Christian Back TUM Physics Department James-Franck-Str. 1 85748 Garching T: +49 89 289-12401 E: christian.back@tum.de W: http://www.spincat.info/ index.php Christian Back is a Full Professor of experimental physics at the Technical University of Munich. He previously worked as a postdoctoral researcher at the Stanford Linear Accelerator Center and IBM San Jose, before taking up a research position at ETH Zurich. He subsequently held a Professorship at the University of Regensburg before taking up his current position in 2017.
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