Thermally excited magnetic waves enable generation of electricity using insulators
The recovery of waste heat in all kinds of processes poses one of the main challenges of our time to making established processes more energy-efficient and thus more environmentally friendly. The Spin Seebeck effect (SSE) is a novel, only rudimentarily understood effect, which allows for the conversion of a heat flux into electrical energy, even in electrically non-conducting materials.
A team of physicists at Johannes Gutenberg University Mainz (JGU), the University of Konstanz, the University of Kaiserslautern, and the Massachusetts Institute of Technology (MIT) have now succeeded in identifying the origin of the Spin Seebeck effect. By the specific investigation of the material- and temperature-dependence of the effect, the German and American researchers were able to show that it exhibits a characteristic length scale attributable to its magnetic origin.
This finding now allows for the advancement of this long-time controversial effect in terms of first applications. The resulting research paper was published in the scientific journal Physical Review Letters, with a fellow of the JGU-based Graduate School of Excellence "Materials Science in Mainz" (MAINZ) as first author.
The Spin Seebeck effect represents a so-called spin-thermoelectric effect, which enables the conversion of thermal energy into electrical energy. Contrary to conventional thermoelectric effects it also enables the recovery of heat energy in magnetic insulators in combination with a thin metallic layer.
Owing to this characteristic, it was assumed that the effect originates from thermally excited magnetic waves. The currently employed method of measurement, which makes use of a second metallic layer converting these magnetic waves into a measurable electrical signal, has so far not been able to allow for a distinct assignment of experimentally detected signals.
By measuring the effect for different material thicknesses in the range of a few nanometers up to several micrometers as well as for different temperatures, the scientists have found characteristic behavior. In thin films the signal amplitude increases with increasing material thickness and eventually saturates after exceeding a sufficient thickness.
In combination with the detected enhancement of this critical thickness at low temperatures, the agreement with the theoretical model of thermally excited magnetic waves developed at Konstanz could be demonstrated. With these results, the researchers were able for the first time to reveal a direct relation between the assumed thermally excited magnetic waves and the effect.
"This result provides us with an important building block of the puzzle of the comprehension of this new, complex effect, unambiguously demonstrating its existence," said Andreas Kehlberger, Ph.D. student at Johannes Gutenberg University Mainz and first author of the publication.
"I am very pleased that this exciting result emerged in a cooperation of a doctoral candidate out of my group at the Graduate School of Excellence 'Materials Science in Mainz' together with co-workers from Kaiserslautern and our colleagues from Konstanz, with whom we collaborate within the Priority Program 'Spin Caloric Transport' funded by the German Research Foundation (DFG)," emphasized Professor Mathias Kläui, director of the MAINZ Graduate School of Excellence based at Mainz University.
"It shows that complex research is only possible in teams, for instance with funding by the German Federal Ministry of Education and Research (BMBF) through the Mainz-MIT Seed Fund."
The MAINZ Graduate School of Excellence was originally approved as part of the Federal and State Excellence Initiative in 2007 and received a five-year funding extension in the second round in 2012 – a tremendous boost for the Mainz-based materials scientists and for the sponsorship of young researchers at JGU.
The MAINZ Graduate School consists of work groups at Johannes Gutenberg University Mainz, the University of Kaiserslautern, and the Max Planck Institute for Polymer Research in Mainz. One of its focal research areas is spintronics, where cooperation with leading international partners plays an important role.
Kehlberger, A. et al.
Length Scale of the Spin Seebeck Effect
Physical Review Letters, 28 August 2015
Professor Mathias Kläui
Condensed Matter Theory Group
Institute of Physics
Johannes Gutenberg University Mainz
55099 Mainz, GERMANY
phone +49 6131 39-23633
http://www.mainz.uni-mainz.de/ (MAINZ Graduate School of Excellence)
http://www.uni-mainz.de/presse/19572_ENG_HTML.php - press release
http://www.iph.uni-mainz.de/index_ENG.php - Institute of Physics at JGU
http://www.klaeui-lab.physik.uni-mainz.de/index.php - Kläui Lab at JGU
http://www.mainz.uni-mainz.de/ - MAINZ Graduate School of Excellence
Petra Giegerich | idw - Informationsdienst Wissenschaft
An innovative high-performance material: biofibers made from green lacewing silk
20.01.2017 | Fraunhofer-Institut für Angewandte Polymerforschung IAP
Treated carbon pulls radioactive elements from water
20.01.2017 | Rice University
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Awards Funding
20.01.2017 | Materials Sciences
20.01.2017 | Life Sciences