Magnetic superstructures as a promising material for 6G technology

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When will 6G become a reality? The competition for the implementation of sixth generation (6G) wireless communication systems requires the development of appropriate magnetic materials. Researchers at Osaka Metropolitan University and colleagues have found unprecedented collective resonance at high frequencies in a magnetic superstructure called a chiral spin soliton lattice (CSL), revealing chiral helimagnets with CSL as a promising material for 6G technology. The study was published in Physical examination letters.

Future communication technologies require expanding the bandwidth from the current few gigahertz (GHz) to over 100 GHz. Such high frequencies are not yet possible, given that existing magnetic materials used in communication equipment can resonate and absorb microwaves up to approximately 70 GHz with a magnetic field of practical strength. Tackling this knowledge and technology gap, a research team led by Professor Yoshihiko Then of Osaka Metropolitan University delved into the helical rotating CSL superstructure.

“CSL has an adjustable periodicity structure, which means that it can be continuously modulated by changing the strength of the external magnetic field,” explained Professor Then. “CSL phonon mode or collective resonance mode – when CSL curves oscillate collectively around their equilibrium position – allows frequency ranges wider than those of conventional ferromagnetic materials.” This phonon mode of CSL is understood theoretically, but has never been observed in experiments.

Searching for CSL phonon mode, the team experimented with CrNb3S6, a typical chiral magnetic crystal that hosts CSL. They first generated CSL in CrNb3S6 and then observes its resonant behavior under a changing force of an external magnetic field. A specially designed microwave circuit was used to detect magnetic resonance signals.

Researchers have observed resonance in three modes, namely “Kitel mode”, “asymmetric mode” and “multiple resonance mode”. In the Kittel mode, similar to that observed in conventional ferromagnetic materials, the resonant frequency only increases if the magnetic field strength increases, which means that creating the high frequencies required for 6G will require an impractically strong magnetic field. The CSL phonon was also not detected in asymmetric mode.

The CSL phonon was detected in the multiple resonance mode; in contrast to what is observed with magnetic materials currently in use, the frequency increases spontaneously when the strength of the magnetic field decreases. This is an unprecedented phenomenon that is likely to increase to over 100 GHz with a relatively weak magnetic field – this amplification is a much-needed mechanism for achieving 6G performance.

“We were able to observe this resonant movement for the first time,” said first author Dr. Yusuke Shimamoto. “Due to its excellent structural controllability, the resonant frequency can be controlled over a wide range up to the sub-terrazz range. This broadband and variable frequency response exceeds 5G and is expected to be used in research and development of next generation communication technologies. ”

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More info:
Y. Shimamoto et al, Observation of collective resonance regimes in a chiral spin soliton lattice with adjustable magnon dispersion, Physical examination letters (2022). DOI: 10.1103 / PhysRevLett.128.247203

Provided by Osaka Metropolitan University

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