Tunable spin polarizations up to 85% have been reported in bulk Co1-x Fex S2. In this paper, we report on the synthesis of polycrystalline Co1-x Fex S2 thin films on Al2O3 (0001) and SrTiO3 (001) by ex situ sulfidation of epitaxial Co1-x Fex. As a function of sulfidation temperature (TS), the films evolve from unreacted Co1-x Fex, through a mixed phase dominated by Co1-xFexS, to single-phase Co 1-xFexS2 at TS 350 °C. At optimized deposition conditions, the films are sulfur stoichiometric, have an average in-plane grain size of 35 nm, surface roughness of 3.7 nm (at a thickness of 56 nm), and are delamination-free up to 300 nm. The Curie temperature, saturation magnetization, resistivity, and magnetoresistance are similar to those of bulk. Significantly, we find 1.0 μB /Co at x=0.15 and a vanishing spin-flip electron-magnon scattering signature in magnetotransport, consistent with the very highly polarized state observed in bulk crystals. Ex situ sulfidation is therefore a simple route to the formation of Co1-x Fex S2 films, opening up the possibility of exploiting this unique material in fundamental studies of heterostructured spintronic devices.
Bibliographical noteFunding Information:
This work was supported primarily by the MRSEC Program of the NSF under Award Nos. DMR-0212302 and DMR-0819885. We would like to thank J. Thomas for assistance with Auger depth profiling, T. Stefanek for assistance in sample preparation, and M. Sharma, M. Torija, J. Parker, and M. Erickson for thoughtful discussions and assistance.