Engineering 101

Magnetic Superstructures and 6G Developers

The race to 6G requires the development of suitable magnetic materials. Scientists from Osaka Metropolitan University detected an unprecedented collective resonance at high frequencies in a magnetic superstructure called a chiral spin soliton lattice (CSL), revealing CSL-hosting chiral helimagnets as a promising material for 6G technology. They published their study in Physical Review Letters.

Communication technologies will require expanding the frequency band from the current few Gigahertz (GHz) to over 100 GHz. Such high frequencies are not yet possible. Magnetic materials used in communication equipment can only resonate and absorb microwaves up to approximately 70 GHz with a practical-strength magnetic field. Researchers from Osaka Metropolitan University delved into the helicoidal spin superstructure CSL, which has a tunable structure in periodicity. The CSL phonon mode, or collective resonance mode, when the CSL’s kinks oscillate collectively around their equilibrium position, allows frequency ranges broader than those for conventional ferromagnetic materials.

The team experimented on CrNb3S6, a typical chiral magnetic crystal that hosts CSL. They first generated CSL in CrNb3S6 and observed its resonance behavior under changing external magnetic field strengths. They used a specially designed microwave circuit to detect the magnetic resonance signals.

The researchers observed resonance in three modes, namely the “Kittel mode,” the “asymmetric mode,” and the “multiple resonance mode.” In the multiple resonance mode, the CSL phonon was detected; the frequency spontaneously increases when the magnetic field strength decreases. This is an unprecedented phenomenon that will possibly enable a boost to over 100 GHz with a relatively weak magnetic field. This boost is a much-needed mechanism for achieving 6G operability.

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