Electron spin resonance study in the chiral ferromagnet Cu₂OSeO₃ using pulsed magnetic fields up to 64 T and terahertz free electron laser

The recent discovery of skyrmions in Cu₂OSeO₃ has established a new platform to create and manipulate skyrmionic spin textures. We use high-field electorn spin resonance (ESR) spectroscopy combining a terahertz free electron laser and pulsed magnetic fields up to 64 T to probe and quantify ist microscopic spin-spin interactions. Besides providing direct access to the long-wavelength Goldstone mode, this technique probes also the high-energy part of the excitation spectrum which is inaccessible by Standard low-frequency ESR. Fitting the behavior of the observed modes in magnetic field to a theroretical Framework establishes experimentally that the fundamental magnetic building blocks of this skyrmionic magnet are rigid, highly entangled and weakly coupled tetrahedra.