Synthesis of highly spin-polarized Co1-xFexS2 thin films for fundamental studies of spintronic devices

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Date/Time:Thursday, 23 Sep 2010 from 4:10 am to 5:00 am
Location:Physics 5
Phone:515-294-5630
Channel:Condensed Matter Physics
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Michael Manno
Department of Chemical Engineering and Materials Science,
University of Minnesota, Minneapolis, MN 55455, USA

Highly spin polarized materials offer many advantages for future spintronic devices. Recently, Co1-xFexS2, an isostructural alloy of CoS2 and FeS2, has been shown to exhibit high, composition tunable, spin polarization (-56 % < P < +85 %) in bulk polycrystals while circumventing many of the traditional problems with half-metallic ferromagnets. These unique characteristics make Co1-xFexS2 an interesting system for fundamental spintronic device studies, although exploitation of these unique properties clearly requires development of a reliable thin film synthesis route. In this work we demonstrate that ex situ sulfidation of Co1-xFex thin films provide such a synthesis method. Detailed structural characterization demonstrates that we can obtain single-phase stoichiometric polycrystalline thin films, while magnetometry and transport measurements confirm bulk-like properties. Moreover, these films were found to exhibit an unexpected low-field hysteretic magnetoresistance (MR), which is proven to be due to spin-dependent intergranular tunneling. The significance of this observation is that it provides a simple probe of P in such thin film samples, which we found to be as high as 90 %. The intergranular tunneling also leads to the emergence of some rich physics in the thin film/low grain size limit, where the Coulomb energy penalty associated with charging of individual grains becomes visible in the transport. In the final part of my talk I will discuss our recent progress with synthesis of such films on GaAs(100) for tunable semiconductor spin injection, where the reactivity of the substrate provides some very significant challenges.