Transparent ferromagnetic and semiconducting behavior in Fe-Dy-Tb based amorphous oxide films

Abstract

We report a class of amorphous thin film material comprising of transition (Fe) and Lanthanide metals (Dy and Tb) that show unique combination of functional properties. Films were deposited with different atomic weight ratio (R) of Fe to Lanthanide (Dy + Tb) using electron beam co-evaporation at room temperature. The films were found to be amorphous, with grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy studies indicating that the films were largely oxidized with a majority of the metal being in higher oxidation states. Films with R = 0.6 were semiconducting with visible light transmission due to a direct optical band-gap (2.49 eV), had low resistivity and sheet resistance (7.15 × 10−4 Ω-cm and ~200 Ω/sq respectively), and showed room temperature ferromagnetism. A metal to semiconductor transition with composition (for R < 11.9) also correlated well with the absence of any metallic Fe0 oxidation state in the R = 0.6 case as well as a significantly higher fraction of oxidized Dy. The combination of amorphous microstructure and room temperature electronic and magnetic properties could lead to the use of the material in multiple applications, including as a transparent conductor, active material in thin film transistors for display devices, and in spin-dependent electronics.

Integration of amorphous ferromagnetic oxides with multiferroic materials for room temperature magnetoelectric spintronics

“…2(c), is of the order of 10 −1 to 10 2 −1 cm −1 and is much higher than those typically observed for systems with SPH conduction (highest being 10 −3 −1 cm −1 for vanadium oxide 41 ), VRH seemed the more likely conduction mechanism. In 3-D VRH, the DC conductivity, is related to the temperature through a parameter, which can be expressed as 1/(d + 1), d being the space dimension of the system [38,39] and 1/4 ≪ 1.0. The value of is largely determined by the localized DOS near the Fermi level, as explained by Singh and Shimakawa 42 .…”

“…We note that in this regard, while a large number of crystalline oxide metals have been explored, amorphous oxides have not been that well studied. Recent reports have emerged of amorphous materials made from iron and lanthanide systems that appear to show promising electronic or magnetic behavior 37,38 and this forms the background for our studies.…”

Same Precursor, Two Different Products: Comparing the Structural Evolution of In–Ga–O “Gel-Derived” Powders and Solution-Cast Films Using Pair Distribution Function Analysis

“…Amorphous metal oxide films exhibit a range of attractive properties for technological applications and are candidate materials for next-generation thin-film devices, such as thin-film transistors. − In particular, amorphous semiconducting oxides such as Zn–O, In–O, amorphous In–Ga–O, amorphous In–Ga–Zn–O, amorphous In–Sn–O, amorphous Zn–In–Sn–O, and amorphous Zn–Sn–O have garnered significant interest. ,,, Such materials have been shown to have high electron mobilities, , tunable conductivity, high optical transparency, , mechanical stress tolerance, ,, and compatibility with organic dielectric and photoactive materials, making them applicable for a number of applications. ,,− The performance of these materials is strongly correlated with the structure and disorder of the material. , However, the inherent complexity of amorphous oxide structures has hindered our understanding of chemical transformations and their influence on structure–property relationships.…”