Lithography-Free Ultrathin Lossless All-Dielectric Material with Magnetic Activity

We report the fabrication of an ultrathin, lossless, all-dielectric ferromagnetic film via the sequential deposition of TiO₂/Y₂O₃/MnO/ZnO (TYMZO) monolayers on silicon (100) substrates by using atomic layer deposition (ALD). The TYMZO films, with controlled thicknesses of 30, 60, and 100 nm, exhibit tunable optical and structural properties. Their composition and structural integrity were confirmed using spectroscopic ellipsometry, UV–vis spectrophotometry, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The extinction coefficient of TYMZO approached zero across the optical spectrum, attributed to the lossless optical properties of its constituent materials. Cross-sectional TEM analysis revealed amorphous phases in films deposited at a substrate temperature of 250 °C, with a well-defined film–substrate interface. The amorphous nature of the TYMZO film, coupled with atomic migration of Ti and Mn, facilitated the formation of ZnO, TiO, and Y₂O₃ clusters as well as the potential formation of Mn-ZnO and Ti-ZnO compounds, which are known for their anisotropic magnetic properties. Magnetic measurements confirmed anisotropic ferromagnetic behavior, likely resulting from Mn-ZnO and Ti-ZnO clusters with nonparallel easy axes. The TYMZO films on silicon exhibited exceptional absorption efficiency across a tunable range of wavelengths. This enhanced absorption is attributed to the localization of optical fields within the lossless TYMZO layer due to Fabry–Perot resonances, which are subsequently absorbed by the lossy silicon substrate. These findings demonstrate the potential of TYMZO films for advanced photonic and magnetic applications, combining lossless optical properties with tunable ferromagnetic behavior.