TORONTO – Spin wave technology goes back decades, but as an alternative to semiconductor circuits that transmit information by electric charges, it’s been hampered by the fact that the properties of its signal propagation vary in different directions — until now.
Researchers at the National University of Singapore (NUS) have developed a method of propagating spin waves that lead to the development of high speed, miniaturized data processing devices, which could have huge potential as memory devices that are more energy efficient, faster and higher in capacity.
Spin wave based devices use collective excitations of electronic spins in magnetic materials as a carrier of information. But as Professor Adekunle Adeyeye from NUS’ department of electrical and computer engineering explained in an interview with EE Times, the technology’s anisotropic signal propagation creates challenges for practical industrial applications of spin wave-based devices.
However, Adeyeye’s research team recently developed a method for the simultaneous propagation of spin wave signals in multiple directions at the same frequency, without the need for any external magnetic field, by using a novel structure comprising different layers of magnetic materials to generate spin wave signals. This approach, he said, allows for ultra-low power operations, making it suitable for device integration as well as energy-efficient operation at room temperature.
Professor Adekunle Adeyeye from the department of electrical and computer engineering at the NUS faculty of engineering leads a team that recently developed a novel method for the simultaneous propagation of spin wave signals in multiple directions at the same frequency without the need for any external magnetic field. Photo Credit: National University of Singapore.Spin-wave devices use collective excitations of electronic spins as a carrier of information, making them an alternative to charge-based semiconductor technology. As explained by Adeyeye, the osotropic in-plane propagating coherent spin waves known as magnons require magnetization to be out of plane in a spin-wave devices. In the paper, he and the team outline how they solved the lack of availability of low-damping perpendicular magnetic material. Typically, a well-known in-plane ferrimagnet yttrium iron garnet (YIG) is used with a large out-of-plane bias magnetic field, which tends to hinder the benefits of isotropic spin waves.
In their experiment, Adeyeye’s team was able to demonstrate a spin-wave device that eliminates the need for external magnetic field to obtain perpendicular magnetization in an otherwise in-plane ferromagnet, Ni80Fe20 or permalloy (Py), a typical choice for spin-wave microconduits. Perpendicular anisotropy in Py was induced by the exchange-coupled Co/Pd multilayer. Isotropic propagation of magnon spin information has been experimentally shown in microconduits with three channels patterned at arbitrary angles.
In the experimental configuration as detailed in the team’s research paper, a laser beam was focused using a 100× objective onto the sample, which is placed on top of a nanopositioning stage. The scattered beam was collected by the same objective and directed toward an interferometer by using a polarizing beam splitter. A white light and a camera are collinearly arranged for positioning and stabilization of the sample. Spin waves were excited by a GSG-type stripe antenna, which is shown to be connected to an RF signal generator.
(A) SEM image of the concept device in which a Co-Pd-Py conduit has three channels at three different angles. Antenna is placed at the three-channel junction. (B) BLS spectra as a function RF recorded at three channels indicated by different symbols in the SEM image. (C) Two-dimensional spin wave intensity maps at 5.7, 6.7, and 8.2 GHz recorded over an area of 3 × 12 µm2. Each pixel corresponds to BLS intensity at that position.The project was supported by the National Research Foundation Singapore’s Competitive Research Program, and the research team’s results have been published in the scientific journal Science Advances with lead author Dr Arabinda Haldar, formerly a Research Fellow with the department at NUS, and now an assistant professor at Indian Institute of Technology Hyderabad. This research project builds on an earlier study by the team that was published in Nature Nanotechnology in 2016, in which a device that could transmit and manipulate spin wave signals without the need for any external magnetic field or current was developed. The research team has filed patents for these two inventions.
Adeyeye said that together these discoveries make on-demand control of spin waves and the local manipulation of information and reprogramming of magnetic circuits possible, which in turn enables the implementation of spin wave-based computing and coherent processing of data. He doesn’t want to speculate how long it might take before the patents lead to actual commercial devices, but the ultimate goal would be for any spin wave devices to be compatible with existing CMOS processes to increase the likelihood of adoption.
For the immediate future, the team is exploring the use of novel magnetic materials to enable coherent long-distance spin wave signal transmission.
—Gary Hilson is a general contributing editor with a focus on memory and flash technologies for EE Times.
Related Articles:
- Quantum Photons Emitted
- 4 Views of the Silicon Roadmap
- 12 Views on the Future of Electronics
- Four Grand Engineering Challenges
- Spin Waves Cut Logic Power