Synthesis And Characterization Of Amorphous Fe2.75dy-Oxide Thin Films Demonstrating Room-Temperature Semiconductor, Magnetism, And Optical Transparency

Recently, amorphous/disordered oxide thin films made from Fe and lanthanides like Dy and Tb have been reported to have a rich set of magnetic, optical, and electronic properties, as well as room-temperature magneto-electric coupling with multiferroics [A. Malasi et al., Sci. Rep. 5, 18157 (2015); H. Taz et al., Sci. Rep. 6, 27869 (2016); and H. Taz et al., Sci. Rep. 10, 1-10 (2020)]. Here, we report the synthesis and detailed characterization of Fe2.75Dy-oxide thin films prepared on various substrates using electron beam co-evaporation. The structure, chemistry, electric, magnetic, and optical properties were studied for the as-prepared and annealed (373K, in air, 1h) films of thickness 40nm. High resolution transmission electron microscopy and electron diffraction study showed that the films were amorphous in both the as-prepared and annealed states. The electron energy-loss spectroscopy studies quantified that metal oxygen stoichiometry changed from Fe2.75Dy-O1.5 to Fe2.75Dy-O1.7 upon annealing. Synchrotron-based x-ray absorption spectroscopy investigation confirmed that the as-prepared films were highly disordered with predominantly metallic Fe and Dy states that became slightly oxidized with annealing in air. The as-prepared amorphous films demonstrated significantly high value of ordinary (similar to 10cm2/Vs) and anomalous (similar to10 2cm2/Vs) Hall mobility and high electrical conductivity ofsimilar to10 3S/cm at room temperature. The cryogenic magnetic property measurement shows two-step magnetization below 200K, suggesting exchange-spring magnetic interaction. The nature of the field cooled and zero-field cooled curves suggested a spin-glass like transition between 78K and 80K, with a characteristic broad peak. The Tauc plot analysis from optical transmission spectra confirms the existence of an optical bandgap ofsimilar to 2.42eV that increased slightly tosimilar to 2.48eV upon annealing. This rich set of transport, optical, and magnetic properties in these thin films is very exciting and points to potential applicability in low-cost multifunctional devices requiring a combination of transparent, semiconducting, and magnetic responses, such as in spintronics.