September 2012

Abstracts of the QSIT Lunch Seminar, September 6, 2012

Magnetic states of individual ferromagnetic nanotube probed by anisotropic magnetoresistance

Daniel Rüffer,  Laboratory of Semiconductor Materials, EPFL 

Co-Authors: R. Huber2, P. Berberich2, E. Russo-Averchi1, M. Heiss1, J. Arbiol3,  A.Fontcuberta I Morral1, D. Grundler1,2, D.Weber4, A.  Buchter4, F. Xue4, M. Poggio4
1 EPFL Lausanne, 2 TU München, Germany, 3 ICREA & ICMAB-CSIC, Bellaterra, Spain, 4 Universität Basel

Future high-density memory elements and spintronic devices are expected to employ nanoscale ferromagnets as basic building blocks. Recently, a novel type of magnetic structure, the ferromagnetic nanotube, has been fabricated. The tubular geometry is interesting as it offers, compared to solid wires, an additional geometrical parameter for tuning the magnetic properties. Furthermore, because such a tube is free of magnetic matter along the axis, Vortex states without magnetic singularity in the core are possible. Hybrid structures consisting of a semiconductor nanowire surrounded by a ferromagnetic nanotube offer novel perspectives for spin injection and spin transport in a one-dimensional electron system.

We report on magnetotransport studies performed on individual ferromagnetic nanotubes deposited on GaAs nanowires with a diameter of 150 nm, grown by molecular beam epitaxy (MBE). The shell of metallic ferromagnet Ni was deposited by atomic layer deposition (ALD). Single tubes were electrically contacted to perform magnetoresistance measurements under varying field orientation in cryogenic environment. We found hysteretic magnetoresistance behavior. Analyzing the peculiar behavior in terms of the anisotropic magnetoresistance in thin films we develop for the first time a classification of relevant magnetization states in the nanotube.

Complementary experiments using cantilever magnetometry on single tubes were performed in collaboration with the group of M. Poggio. The results will be briefly discussed.

References:

  • Rüffer et al., Nanoscale 2012, 4, 4989-4995
  • Weber at al., in review

Ultra-High Quality Factor Single-Crystal Diamond Nanoresonator

Ye Tao, Spin Physics and Imaging - Degen Lab, ETHZ

Diamond has a reputation as a uniquely versatile material, yet one that is intricate to grow and process. Single-crystal diamond nanostructures are expected to possess superb mechanical properties, including high quality factors and low dissipation. In this talk, we show two routes to batch-fabricate single-crystal diamond nanocantilevers as thin as 85 nm and with lateral dimensions up to 240 um. Quality factors (Q) exceeding 5 million and dissipation levels in the range of 10-14 kg/s are found, resulting in a force sensitivity of a few attonewtons (1 aN = 10-18 N) per root Hz at 4K, and a few hundred zeptonewtons (1 zN = 10-21 N) per root Hz at millikelvin temperatures. These values surpass force sensitivities achieved with state-of-the-art silicon cantilevers of similar dimensions by up to an order of magnitude. We have also investigated the effect of diamond material quality and surface chemistry on the Q factor so as to gain insights into the causes of mechanical dissipation. These insights will possibly allow further improvement of these amazing mechanical devices. Combination of single-crystal diamond nanoresonators with photonic structures or optical and magnetic defects may well lead to revolutionary applications in classical and quantum science.

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