Berlin 2012 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 4: Spin-dependent Transport Phenomena
MA 4.5: Vortrag
Montag, 26. März 2012, 10:30–10:45, H 1012
Tunnel-induced spin-anisotropy in quantum dot spin valves — •Maciej Misiorny1, Michael Hell1, and Maarten Wegewijs1,2 — 1Peter Grünberg Institut, Forschungszentrum Jülich & JARA Jülich Aachen Research Alliance, 52425 Jülich, Germany — 2Institute for Theory of Statistical Physics, RWTH Aachen, 52056 Aachen, Germany
Atomic-scale spintronic systems, such as single-molecule magnets (SMMs) and magnetic adatoms, have recently been studied intensely mainly because of their large spin-anisotropy arising from strong spin-orbit and ligand fields. We show that spin-anisotropy can also be generated in spin-isotropic systems by spin-dependent transport of electrons. For a generic spin-1 quantum dot tunnel coupled to two metallic ferromagnetic electrodes we show that quantum fluctuations induce a quadrupolar exchange field, generalizing the well established (dipolar) exchange field. This field generates a uniaxial spin-anisotropy barrier that increases with the tunnel coupling, achieving values comparable to that of SMMs, but with the added flexibility of electric and magnetic tuneability. Besides inducing it, the transport can also be used to directly read out the quadrupolar field, utilizing its competition with Kondo spin-exchange processes with the ferromagnets. In this regime the proximity-induced quadrupolar exchange field is found to dominate over the dipolar exchange field, strongly enhancing the low-temperature spin-filtering as compared to spin-1/2 quantum dot spin-valves. Consequently, not only do spin-quadrupole effects in spin-polarized transport seem inevitable in high-spin nanosystems, but they also offer new prospects for spintronic applications.