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MM: Fachverband Metall- und Materialphysik

MM 8: Topical Session Nanoporous Functional Materials III

MM 8.2: Topical Talk

Montag, 23. März 2009, 15:15–15:45, IFW A

Porous silicon as functionalized magnetic material — •Heinz Krenn, Klemens Rumpf und Petra Granitzer — Institut für Physik, Bereich Experimentalphysik, Karl-Franzens-Universität Graz

Porous silicon prepared as a template for 1D wires or as 3D particles is increasingly used for gas testing, micro devices, batteries and for biological testing equipment. The focus of the present study will be on magnetic functionalization: The electrochemical synthesis of mesoporous silicon allows tailored pore sizes for a controllable inclusion of magnetic transistion metals (Ni, Co). The corresponding spin magnetism is well understood for magnetic fields below 1 Tesla. Interestingly for high fields (> 3T) a novel kind of orbital magnetism [1] is observed mediated by spin injection from the metal into the silicon matrix (which is still crystalline) driven by impurity assisted tunneling. In the same way as electrochemical etching is self-limited by forming a depletion layer, the silicon matrix becomes intrinsic. Due to quantum and dielectric confinement the energy levels of ionized impurities are blue-shifted. If these levels are resonant with the Fermi-level of Ni or Co wire, unbalanced spins are injected and persistent currents around the wires cause orbital paramagnetism in the symmetry-breaking electric field of the interface barrier. Strange effects are observed: negative magnetization in the hysteresis loop, non-saturation up to 7 T, and suppression of orbital magnetism under cyclotron resonance conditions. [1] K. Rumpf, P. Granitzer, H. Krenn, J. Phys.: Condens. Matter 20 (2008) 454221. (Work supported by the Austrian Science Fund under grant P18593).