Anticrossing behavior between magnons in the noncollinear chiral magnet ${\mathrm{Cu}}_2{\mathrm{OSeO}}_3$ and a two-mode $X$-band microwave resonator was studied in the temperature range 5–100 K. In the field-induced ferrimagnetic phase, we observed a strong-coupling regime between magnons and two microwave cavity modes with a cooperativity reaching 3600. In the conical phase, cavity modes are dispersively coupled to a fundamental helimagnon mode, and we demonstrate that the magnetic phase diagram of ${\mathrm{Cu}}_2{\mathrm{OSeO}}_3$ can be reconstructed from the measurements of the cavity resonance frequency. In the helical phase, a hybridized state of a higher-order helimagnon mode and a cavity mode—a helimagnon polariton—was found. Our results reveal a class of magnetic systems where strong coupling of microwave photons to nontrivial spin textures can be observed.

• Received 20 February 2018
• Revised 15 June 2018

DOI:https://doi.org/10.1103/PhysRevB.99.140401