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Exchange Coupling and Spin Transport in Hybrid Spintronic Devices

Nitin Samarth

Studies of exchange interactions and spin transport in heterogeneous materials have evoked long-standing interest in condensed matter physics for both fundamental and technological reasons. For instance, exchange-biased spin valves and magnetic tunnel junctions that incorporate ferromagnetic (and antiferromagnetic) metals with conventional metals (and insulators) form the backbone of mainstream spintronics technology. On the other hand, the juxtaposition of ferromagnets with superconductors has been driven by more fundamental questions, ranging from the precise measurement of spin polarization to the search for new phenomena created by competing order parameters. In this general context, we have been exploring spin-dependent phenomena in a variety of hybrid magnetic/semiconductor and magnetic/superconductor systems of varying scale and dimensionality. This talk provides a thematic motivation for such a program and describes the implications for spintronics, with glimpses of key results from some of our recent explorations. Using magnetometry and transport measurements in macro- and meso-scale metal/semiconductor spin valves and tunnel junctions, we develop a comprehensive picture of interfacial and interlayer exchange coupling in a regime distinct from analogous all-metal devices [1-4]. We also briefly describe emerging opportunities in “nanospintronics,” driven by the synthesis of axially- and radially-modulated magnetic/ semiconductor nanowires [5,6] and by the observation of long-ranged proximity effects in superconductor/ferromagnet nanostructures [7].

1. M. Zhu et al., Appl. Phys. Lett. 91, 192503 (2007).
2. M. Zhu et al., Phys. Rev. B 78, 195307 (2008).
3. M. J. Wilson et al., Phys. Rev. B 81, 045319 (2010).
4. P. Mitra et al., (in preparation, 2010).
5. B. J. Cooley et al., Nano Lett. 9, 3142 (2009).
6. N. Dellas et al., (submitted, 2010).
7. J. Wang et al., Nature Physics, 6, 389 (2010).