Magnetic superstructures as a promising material for 6G technology

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When will 6G be a reality? The race to realize sixth generation (6G) wireless communication systems requires the development of suitable magnetic materials. Scientists at Osaka Metropolitan University and their colleagues have detected an unprecedented high-frequency collective resonance in a magnetic superstructure called the chiral spin soliton (CSL) lattice, revealing that chiral heliimans hosting CSLs are a promising material for 6G technology. The study was published in Physical Review Letters.

Future communication technologies require expanding the frequency band of the current few gigahertz (GHz) to more than 100 GHz. These high frequencies are not yet possible, since existing magnetic materials used in communication equipment can only resonate and absorb microwaves up to about 70 GHz with a magnetic field of practical strength. Addressing this gap in knowledge and technology, the research team led by Professor Yoshihiko Togawa of Osaka Metropolitan University delved deeper into the CSL helical twist superstructure.

“CSL has a periodicity-tunable structure, which means it can be continuously modulated by changing the strength of the external magnetic field,” Professor Togawa explained. “The CSL phonon mode, or collective resonance mode, when CSL kinks collectively oscillate around their equilibrium position, allows for wider frequency ranges than conventional ferromagnetic materials.” This CSL phonon mode has been understood theoretically, but has never been observed in experiments.

Searching for the CSL phonon mode, the team experimented with CrNb3yes6, a typical chiral magnetic crystal harboring CSL. They first generated CSL on CrNb3yes6 and then observed their resonance behavior under changing external magnetic field forces. A specially designed microwave circuit was used to detect the MRI signals.

The researchers looked at the resonance in three modes, namely the “Kittel mode”, the “asymmetric mode” and the “multiple resonance mode”. In the Kittel mode, similar to what is seen in conventional ferromagnetic materials, the resonance frequency increases only if the magnetic field strength increases, meaning that creating the high frequencies needed for 6G would require an impractical magnetic field. The CSL phonon was also not found in the asymmetric mode.

In multiple resonance mode, the CSL phonon was detected; Unlike what is observed with magnetic materials currently in use, the frequency increases spontaneously when the intensity of the magnetic field decreases. This is an unprecedented phenomenon that will possibly allow a boost to over 100 GHz with a relatively weak magnetic field; this boost is a much-needed mechanism to achieve 6G operability.

“We managed to observe this resonance motion for the first time,” said first author Dr. Yusuke Shimamoto. “Due to its excellent structural controllability, the resonant frequency can be controlled in a wide band up to the sub-terahertz band. This wide-band and variable-frequency characteristic exceeds 5G and is expected to be used in research and development of next-generation communication technologies.

New monochromatic phonon-based, magneto-tunable terahertz source

More information:
Y. Shimamoto et al, Observation of collective resonance modes in a chiral-spin soliton lattice with tunable magnon scattering, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.128.247203

Provided by Osaka Metropolitan University

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