A New Magnetic Phase and Magnetic Interactions in Skyrmionic Insulator Cu₂OSeO₃

Copper(II) oxy-selenite (Cu₂OSeO₃), unlike most skyrmionic materials which are metallic, is an insulating and structurally chiral compound with several strong infrared-active phonons that exhibit anomalous behavior across multiple magnetic transitions at low temperatures and fields. Most previous spectroscopic studies have focused on its skyrmionic nature at low fields and frequencies. Here, we present experimental data from circular and vortex polarized magneto-infrared transmission in the Voight and Faraday configurations, ellipsometry, and circularly polarized Raman spectroscopy, revealing a new magnetic phase that develops above 2 T, characterized by distinct magnetic modes and phonon interactions. In the Faraday configuration we observed strong circular and vortex-beam dichroism for the coupled magnetic-phonon modes in magnetic fields up to 7 T.