Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session T1: Probes of Nanoscale Magnetism |
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Sponsoring Units: DCMP Chair: Chris Hammel, Ohio State University Room: Spirit of Pittsburgh Ballrom A |
Wednesday, March 18, 2009 2:30PM - 3:06PM |
T1.00001: Chiral magnetic order at surfaces driven by inversion asymmetry Invited Speaker: |
Wednesday, March 18, 2009 3:06PM - 3:42PM |
T1.00002: Ultrasensitive magnetometry and magnetic resonance imaging using cantilever detection Invited Speaker: Micromachined cantilevers make remarkable magnetometers for nanoscale measurements of magnetic materials and for magnetic resonance imaging (MRI). We present various applications of cantilever magnetometry at low temperature using cantilevers capable of attonewton force sensitivity. Small, unexpected magnetic effects can be seen, such as anomalous damping in magnetic field. A key application is magnetic resonance force microscopy (MRFM) of both electron and nuclear spins. In recent experiments with MRFM-based NMR imaging, 3D spatial resolution better than 10 nm was achieved for protons in individual virus particles. The achieved volumetric resolution represents an improvement of 100 million compared to the best conventional MRI. The microscope is sensitive enough to detect NMR signals from adsorbed layers of hydrocarbon contamination, hydrogen in multiwall carbon nanotubes and the phosphorus in DNA. Operating with a force noise on the order of 6 aN per root hertz with a magnetic tip that produces a field gradient in excess of 30 gauss per nanometer, the magnetic moment sensitivity is $\sim $0.2 Bohr magnetons. The corresponding field sensitivity is $\sim $3 nT per root hertz. To our knowledge, this combination of high field sensitivity and nanometer spatial resolution is unsurpassed by any other form of nanometer-scale magnetometry. [Preview Abstract] |
Wednesday, March 18, 2009 3:42PM - 4:18PM |
T1.00003: Ferromagnetic Resonance Imaging with Magnetic Resonance Force Microscopy Invited Speaker: Magnetic resonance force microscopy achieves very high resolution three-dimensional imaging capabilities of magnetic resonance imaging by taking advantage of very high sensitivity mechanical force detection. This enables non-contacting, microscopic studies and imaging of a broad range of materials. As a consequence of the strong interactions between spins, the assumptions underlying conventional MRI are not applicable to FMR imaging. However, using a new approach to localizing the resonant volume in an FMR measurement founded on the strong, nonuniform magnetic field of the micromagnetic probe tip, we have demonstrated scanned probe Ferromagnetic Resonance (FMR) imaging [1]. The scanned probe FMR images obtained in patterned ferromagnetic films are well explained by detailed numerical modeling. In addition to illuminating the mechanisms underlying localized FMR, the model provides the basis for submicron scanned probe FMR imaging of films and buried ferromagnetic elements. This work was supported by the U.S. Department of Energy through Grant No. DE-FG02-03ER46054. \newline \newline [1] ``Local Ferromagnetic Resonance Imaging with Magnetic Resonance Force Microscopy,'' Yu. Obukhov, D.V. Pelekhov, J. Kim, P. Banerjee, I. Martin, E. Nazaretski, R. Movshovich, S. An, T.J. Gramila, S. Batra, and P. C. Hammel, Phys. Rev. Lett. \textbf{100}(19), 197601 (2008). [Preview Abstract] |
Wednesday, March 18, 2009 4:18PM - 4:54PM |
T1.00004: Ultrafast magnetization dynamics of cobalt nanoparticles and individual ferromagnetic dots Invited Speaker: The ultrafast magnetization dynamics of magnetic materials can be investigated using femtosecond laser pulses to perform femtosecond magneto-optical Kerr and Faraday measurements [1]. In this talk, we will focus on the magnetization dynamics of cobalt nanoparticles which are either ferromagnetic or super-paramagnetic at room temperature and on the dynamics of individual ferromagnetic dots. In the first case (Co nanoparticles), we will demonstrate that the magnetization dynamics preceding the fluctuations over the anisotropy energy barrier is coherent but exhibits a strongly damped precession [2]. These results, which have been obtained with a three dimensional analysis of the magnetization vector [3] will be discussed in the context of the N\'{e}el-Brown models involving the gyromagnetic character of the magnetization. We will also examine the dynamics of self-organized supra-crystals of cobalt nanoparticles [4]. In the second case, we will present the ultrafast magnetization dynamics of individual ferromagnetic dots (CoPt$_{3}$, Permalloy, Nickel) made either by e-beam lithography or induced optically on thin films deposited on sapphire and glass substrates. The technique employed is the magneto-optical pump probe imaging (MOPPI) which allows performing time resolved magneto-optical Kerr images with with spatial and temporal resolutions of 300 nm and 150 fs [5]. The study of the demagnetization of the dots for different laser intensities shows that it is possible to write and read ultrafast monodomains on thin films. \\[3pt] [1] E. Beaurepaire, J.-C. Merle, A. Daunois, J.-Y. Bigot~ Phys. Rev. Lett., \textbf{76}, 4250 (1996) \\[0pt] [2] L.H.F. Andrade, A. Laraoui, M. Vomir, D. Muller, J.-P. Stoquert, C. Estourn\`{e}s, E.~Beaurepaire, J.-Y. Bigot Phys. Rev. Lett. \textbf{97}, 127401 (2006). \\[0pt] [3] M. Vomir, L. H.F. Andrade, L. Guidoni, E. Beaurepaire, J.-Y. Bigot Phys. Rev. Lett. \textbf{94}, 237601 (2005). \\[0pt] [4] I.~Lisiecki, V.~Halt\'{e}, C. Petit, M.-P.~Pileni, J.-Y.~Bigot Adv. Mater., \textbf{20}, 4176 (2008). \\[0pt] [5] A. Laraoui, M. Albrecht, J.-Y. Bigot Optic. Letters \textbf{32}, 936 (2007). [Preview Abstract] |
Wednesday, March 18, 2009 4:54PM - 5:30PM |
T1.00005: Magnetic soft X-ray microscopy: Towards imaging ultrafast spin dynamics on the nanoscale Invited Speaker: Modern magnetic microscopies are challenged with providing spatial resolution in the nanometer regime, a time resolution on a fs scale and elemental specificity to allow for studying multifunctional magnetic nanostructures and their ultrafast spin dynamics. Magnetic soft X-ray microscopy combines X-ray magnetic circular dichroism (X-MCD) as element specific magnetic contrast mechanism with high spatial and temporal resolution. Fresnel zone plates provide a spatial resolution down to currently $<$15nm [1] with current developments approaching the 10nm regime thus approaching fundamental magnetic length scales. Utilizing the inherent time structure of current synchrotron sources fast magnetization dynamics with 70ps time resolution, limited by the lengths of the electron bunches, can be performed with a stroboscopic pump-probe scheme. Soft x-ray microscopy at upcoming high brilliant fsec X-ray sources makes snapshot images of fsec spin dynamics feasible. In this talk I will present recent results on the study of the stochastical character in magnetization reversal and domain wall pinning [2] as well as on time resolved imaging of current induced resonant vortex core motion which allows to determine spin polarization of currents [3] \\[4pt] [1] D.-H. Kim, et al., J. Appl. Phys. 99, 08H303, (2006) \\[0pt] [2] M.-Y. Im et al, Adv. Mater 20 1750 (2008) \\[0pt] [3] S. Kasai et al. Phys Rev Lett (2008) accepted [Preview Abstract] |
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