Magnetism offers new possibilities to develop more powerful and energy-efficient computers, but the realisation of magnetic computing on the nanoscale is a challenging task. A research team from Kaiserslautern, Jena and Vienna reports on a decisive progress in the field of calculations with ultra-low power requirements using magnetic waves in the journal Nano Letters.
A local disturbance in the magnetic order of a magnet can propagate in waves over a material. These waves are called spin waves and the associated quasi-particles are called magnons. Scientists of the Technical University of Kaiserslautern, Innovent e.V. from Jena and the University of Vienna are known for their Expertise in the research field "Magnonics". Here, magnons are used for the development of new types of computers which may complement the electron-based processors in use today.
"A new generation of computers with magnons could be more powerful and, above all, consume less energy. An important prerequisite is that we must be able to produce so-called monomode waveguides, which enable us to use advanced wave-based signal processing schemes", says junior professor Philipp Pirro, one of the project's leading scientists. "To do this, the dimensions of our structures in the nanometer range. The development of such data lines opens up an access to develop neuromorphic computer systems based on the function of the human brain"..
However, scaling the magnonics technology to the nanoscale is a challenge: "A very Yttrium-iron-garnet (YIG) is a promising material for magnetic applications. YIG is a kind of 'noble magnetic material' because magnons survive in it about a hundred times longer than in other materials," says the Project leader, Professor Andrii Chumak from the University of Vienna. "But everything has its price: YIG is very complex and difficult to handle when you try to make tiny structures out of it. Therefore YIG structures were millimetre in size for decades, and only now have we succeeded in going down to 50 nanometres, which is about is 100,000 times smaller."
For this purpose, a special new technology was developed at the Nano Structuring Center of the Technical University of Kaiserslautern in which the YIG layers cultivated by Dr. Carsten Dubs from Innovent e.V. in Jena can be used. A thin metal layer, a so-called mask, is applied to this YIG layer, which leaves most of this layer free. The sample is then bombarded with a strong stream of argon ions, which unprotected parts of the YIG layer are removed, while the material under the mask remains intact Afterwards removes the metal mask, revealing a 50 nm thin strip of the finished YIG layer.
"A crucial factor for the success of the whole process was to find the right materials for the mask, to find out how thick it has to be, and set dozens of different parameters to adjust the properties of a YIG layer," says Björn Heinz, the lead author of the paper. "After several years investigations, we have finally found the appropriate process, a combination of chrome and titanium layers. The width of the YIG structure is about a thousand times smaller than the thickness of a human hair. According to the successful structuring, scientists continued to study the propagation of magnons to test whether the nano-sized YIG structures retain the superior material properties of the YIG layers.
"We were able to show that the structuring process has only a minor influence on the fantastic properties of this material," says Heinz. "Furthermore, we were able to prove experimentally that magnons transport information efficiently over long distances in the pipelines, as was previously the case in theory was claimed. These results are an important step in the development of magnonic circuits and prove the general feasibility of magnon-based data processing".
The research was funded under the ERC Starting Grant MagnonCircuits (A. Chumak), the Collaborative Research Centre SFB 173 Spin+X (P. Pirro) and the DFG project DU 1427/2-1 (C. Dubs) and funded by the State Research Centre OPTIMAS.
The results were published in the journal Nano Letters:
Jun.-Prof. Dr. Philipp Pirro
Technische Universität Kaiserslautern
Tel.: +49 631 205 4092
Univ.-Prof. Dr. habil. Andrii Chumak
Tel.: +43 1 4277-73910