Electrically Modulated Multilevel Optical Chirality in GdFeCo Thin Films

This study introduces a simple approach to dynamically control multilevel optical ellipticity in ferrimagnetic GdFeCo alloys by switching the spin orientation through Joule heating induced by electrical current, with the assistance of a low magnetic field of 3.5 mT. It is demonstrated that selecting specific compositions of Gd x (FeCo)100-x alloys, with magnetic compensation temperatures near or above room temperature, allows for significant manipulation of the circular dichroism (CD) effect. This control enables the transformation of transmitted light from linearly polarized to elliptically polarized or the reversal of the rotation direction of elliptically polarized light across the photon energy range from visible (vis) to ultraviolet (UV). The efficacy of this method is rooted in the dominant contributions of FeCo to the CD effect in the vis-to-UV energy range. Because the magnetization of FeCo remains relatively independent of the temperature, substantial optical ellipticity is maintained for optical device applications, regardless of whether the compensation temperature is approached or crossed. Our results highlight the potential of GdFeCo thin films in chiral optics and demonstrate the selective contributions of rare-earth transition-metal elements to the CD effects, facilitating the design of advanced optical devices leveraging energy-resolved CD phenomena.