Magnetoresistive detection of spin waves

Spin waves, or ‘magnons’, are local vibrations in the magnetisation of magnetic materials. It has recently been proposed to use them in new information processing architectures known as ‘magnonic’, which would combine the ease of interconnection of wave systems with the information storage capabilities of magnetic systems. To do this, they need to be interfaced with microelectronic circuits, which involves converting these spin waves into an electrical signal at a nanometric scale relevant to current technologies. The techniques used to date - such as optical imaging or inductive detection - have struggled to capture these waves at sub-micrometric scales. 

The present study was carried out in the following CNRS laboratories:

• Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS, CNRS/Université de Strasbourg)
• Service de physique de l'état condensé (SPEC, CEA/CNRS)

Researchers have developed a new method for effectively detecting spin waves as part of the national PEPR Spin programme. The team integrated a giant magnetoresistance sensor directly under a waveguide. When the waves pass close to the sensor, they cause the magnetisation of one of the sensor's layers to oscillate slightly. This causes the sensor's electrical resistance to change, and this variation is converted into a measurable signal at a frequency of several gigahertz. Using this device, the researchers measured a signal fifty times stronger than that obtained with the inductive method, for an equivalent detection surface area. This measurement shows that magnetoresistive detection works remarkably well at the nanometric scale and for these very high frequencies. The researchers also confirmed these results through numerical simulations that accurately reproduce the behaviour observed in the laboratory.

By using more sensitive sensors, such as tunnel magnetoresistance sensors, it would even be possible to increase the signal further. This innovation paves the way for ultra-compact spin wave sensors capable of operating in extreme conditions (at scales smaller than 100 nm, or using spin waves generated by thermal fluctuations, for example). It could also make it easier to integrate magnonics into conventional electronic circuits, enabling the design of new architectures that are faster and more energy efficient. These results are published in the journal Science Advances.