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

H Taz,D Kumar,T Sakthivel,S Seal,C Carr,N K Yamoah,R Kalyanaraman

doi:10.1038/srep27869

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.

Highlights

The films were found to be homogeneous in composition and had amorphous microstructure
Chemical analysis by X-ray photoelectron spectrometer (XPS) studies showed that while the metal cation fraction increased with decreasing atomic ratio Fe:(Dy +Tb), all the films had a large fraction of oxidized metal (≥66%)
XPS valence band edge analysis suggested that high iron compositions were metallic while the high Lanthanide composition was semiconducting

Summary

Introduction

Thin films with varying composition atomic ratio of Fe:(Dy +Tb) (atomic percentages) were fabricated at room temperature. These properties were supported by optical transmission and electrical resistivity measurements of the films. The finding of the composition-tunable metallic-semiconducting behavior, as well as the presence of room temperature ferromagnetism, optical transparency, and semiconducting behavior suggests the following: the combination of Fe with the Lanthanides (Dy and Tb) can lead to a class of materials with a range of multifunctional applications in the amorphous phase.

Results

Conclusion