Regensburg 2010 – scientific programme

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MA: Fachverband Magnetismus

MA 16: Micro- and Nanostructured Magnetic Materials II

MA 16.7: Talk

Wednesday, March 24, 2010, 11:45–12:00, H23

Semiconductor-ferromagnet core-shell nanowires grown by molecular beam epitaxy — •Maria Hilse, Yukihiko Takagaki, Jens Herfort, Claudia Herrmann, Manfred Ramsteiner, Steffen Breuer, Lutz Geelhaar, and Henning Riechert — Paul-Drude-Institut für Festkörperelektronik, Berlin

The special geometry of nanowires (NWs) offers the possibility to elastically absorb lattice mismatch strain. Thus, axial and radial NW heterostructures consisting of dissimilar materials can be grown with high quality. In addition, spin dependent functionalities are introduced to NW devices when a ferromagnet is incorporated into these heterostructures. MnAs is one of the attractive materials as it is ferromagnetic at room temperature (the Curie temperature is about 40 °C). In this work, we combine GaAs and MnAs in a NW core-shell geometry by means of molecular beam epitaxy (MBE). The GaAs NWs were grown using the Au-assisted vapor-liquid-solid mechanism on GaAs(111)B substrates. The MnAs growth took place under the typical conditions for planar growth on GaAs. A curving of the NWs is observed if the sample stage is not rotated during MnAs overgrowth, evidencing the diffusion length of Mn being less than the perimeter of the NWs. By analyzing the planar film and NW shell thicknesses, we demonstrate the MnAs growth to take place by direct deposition on the NW sidewalls. NWs exhibit a hexagonal cross section indicating the c-axis, i.e., the magnetic hard axis of MnAs to be parallel to the NW axis. This orientation is confirmed by magnetization measurements and magnetic-force microscopy.