A group of scientists from the University of Gothenburg and the Royal Institute of Technology (KTH) have become the first group in the world to demonstrate that theories about nanoscale spin waves agree with observations. This opens the way to replacing microwave technology in many applications, such as mobile phones and wireless networks, by components that are much smaller, cheaper, and that require less resources.
The research group has used one of the three advanced spin wave microscopes in the world, at the university in the Italian town of Perugia, to visualise the motion. The microscope makes it possible to see the dynamic properties of components with a resolution of approximately 250 nanometre.
Schematic sample layout.
Spin torque oscillators with nanoscale electrical contacts are able to produce coherent spin waves in extended magnetic films, and offer an attractive combination of electrical and magnetic field control, broadband operation fast spin-wave frequency modulation, and the possibility of synchronizing multiple spin-wave injection sites. However, many potential applications rely on propagating (as opposed to localized) spin waves, and direct evidence for propagation has been lacking. Here, we directly observe a propagating spin wave launched from a spin torque oscillator with a nanoscale electrical contact into an extended Permalloy (nickel iron) film through the spin transfer torque effect. The data, obtained by wave-vector-resolved micro-focused Brillouin light scattering, show that spin waves with tunable frequencies can propagate for several micrometres. Micromagnetic simulations provide the theoretical support to quantitatively reproduce the results.
Magnonics may give smaller and cheaper components
The results have opened the way for a new field of research known as “magnonics”, using nanoscale magnetic waves.
“I believe that our results will signal the start of a rapid development of magnonic components and circuits. What is particularly exciting is that these components are powered by simple direct current, which is then converted into spin waves in the microwave region. The frequency of these waves can be directly controlled by the current. This will make completely new functions possible”, says Johan Åkerman, who is looking forward to exciting developments in the next few years.
Its magneto-optical and metallic properties mean that magnonic technology can be integrated with traditional microwave-based electronic circuits, and this will make completely untried combinations of the technologies possible. Magnonic components are much more suitable for miniaturisation than traditional microwave technology.