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Research

Magnon spintronics

In the field of magnon spintronics, we study the transport and properties of spin waves (also called magnons). Magnons are the excited states in magnetic materials, and can be thought of as a wave of neighbouring electron spins precessing at the same frequency but with a different phase, as shown in figure 1. They arise because neighbouring electron spins interact strongly in a magnet, making it energetically favourable to excite the collective magnon mode, rather than flipping a single spin (figure 1b and 1c).

Magnons open up the possibility to transmit and manipulate information in a new class of materials: magnetic insulators. While no electric currents can flow in these materials, it turns out that we can send a flow of magnons through a magnetic insulator. The magnons carry a spin current; a flux of angular momentum, that can be used to encode information.

Simple picture of a ferromagnet. (a) Ground state of the magnet: All spin are aligned. (b) Excited state of the magnet: one spin is flipped. (c) Magnon excited state with a lower energy than in (b): Instead of flipping one spin, the net spin reduction is distributed over the whole system. The spins are rotating (precessing) around their equilibrium, forming a magnon.
Simple picture of a ferromagnet. (a) Ground state of the magnet: All spin are aligned. (b) Excited state of the magnet: one spin is flipped. (c) Magnon excited state with a lower energy than in (b): Instead of flipping one spin, the net spin reduction is distributed over the whole system. The spins are rotating (precessing) around their equilibrium, forming a magnon.

Interface with electronics

Magnon spintronics studies magnon spin currents and aims to integrate this technology with conventional electronic devices: It was recently shown in our group that it is possible to transmit an electronic signal using magnon spin currents, by converting an electric current into a magnon spin current and vice versa. Besides, by modifying the interface between electron and magnon spin current, the transport of magnons can be further manipulated. This makes magnon spintronics an interesting field with great potential for applications.

Magnon Hall effect

Magnons in magnetic insulators can also show the Hall effect, similar to electrons in metals. This means that magnons will obtain a transverse velocity while traveling under the influence of an effective magnetic field. This is due to either asymmetric spin-orbit scattering, also called Dzyaloshinskii-Moriya interaction, or dipolar interaction. We study this effect to investigate the interaction of magnons with magnetic fields, and to identify the role of spin-orbit scattering in our materials.

Spin Seebeck effect

Another technologically interesting phenomenon in the field is the spin Seebeck effect: applying a temperature gradient to the magnetic insulator will result in a magnon spin current flowing parallel to this gradient. This is very much analogous to the “ordinary” Seebeck effect, where a temperature gradient over a metal generates an electric current. Due to the favourable scaling of the spin Seebeck power with device area, this effect could find applications in energy harvesting from waste heat. In our group, we study this effect to understand its origin and quantify the relevant parameters, such as the magnon heat conductivity and the spin Seebeck coefficient.

Artisti impression of a device using magnons for signal transmission. An electric current I is converted to a magnon spin current in the bottom part of the device. The spin wave transmits the signal through the magnetic insulator, and is converted back to an electric signal in the top part. This is observed as a voltage V over the two top contacts.
Artisti impression of a device using magnons for signal transmission. An electric current I is converted to a magnon spin current in the bottom part of the device. The spin wave transmits the signal through the magnetic insulator, and is converted back to an electric signal in the top part. This is observed as a voltage V over the two top contacts.

Bachelor and Master projects

We have several projects available on this topic. Projects involve:

  • Fabrication of devices using state-of-the-art nanofabrication technology
  • Performing electronic measurements in our room temperature or cryogenic measurement setups
  • Data analysis and visualisation
  • Possible contribution to a scientific publication

Please contact Ludo Cornelissen (l.j.cornelissen@rug.nl) or Bart van Wees (b.j.van.wees@rug.nl) in case you are interested.

Publications

  1. L.J. Cornelissen, J. Liu, R.A. Duine, J. Ben Youssef and B.J. van Wees, “Long-distance transport of magnon spin information in a magnetic insulator at room temperature”, Nature Physics 11, 1022-1026 (2015)
  2. L.J. Cornelissen and B.J. van Wees, “Magnetic field dependence of the magnon spin diffusion length in the magnetic insulator yttrium iron garnet”, Physical Review B 93, 020403(R) (2016)
  3. L.J. Cornelissen, K.J.H. Peters, G.E.W. Bauer, R.A. Duine and B.J. van Wees, "Magnon spin transport driven by the magnon chemical potential in a magnetic insulator", Physical Review B 94, 014412 (2016)
  4. L.J. Cornelissen and B.J. van Wees, "Temperature dependence of the magnon spin diffusion length and magnon spin conductivity in the magnetic insulator yttrium iron garnet", arXiv:1607.01506 (2016)
  5. J. Shan, L.J. Cornelissen, N. Vlietstra, J. Ben Youssef, T. Kuschel, R.A. Duine, and B.J. van Wees, "Influence of yttrium iron garnet thickness and heater opacity on the nonlocal transport of electrically and thermally excited magnons", arXiv:1608.01178 (2016)

The magnon spintronics team

  • Ludo Cornelissen – PhD student
  • Jing Liu – PhD student
  • Juan Shan – PhD student
  • Timo Kuschel - Postdoc
  • Bart van Wees – Professor and group leader
Laatst gewijzigd:24 augustus 2016 12:22