Bulletin of the American Physical Society
Fall 2009 Meeting of the Four Corners Section of the APS
Volume 54, Number 14
Friday–Saturday, October 23–24, 2009; Golden, Colorado
Session B4: Magnetic Materials |
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Chair: Gary Wysin, Kansas State University Room: Parker Student Center Ballroom E |
Friday, October 23, 2009 2:10PM - 2:22PM |
B4.00001: Ultrafast Magnetization Dynamics Probed at Elemental M-edges of Ni and Fe Using Tabletop High-Order Harmonic EUV Light Chan La-o-vorakiat, Stefan Mathias, Patrik Grychtol, Roman Adam, Mark Siemens, Justin Shaw, Hans Nembach, Claus Schneider, Martin Aeschlimann, Thomas Silva, Margaret Murnane, Henry Kapteyn We show for the first time that EUV light generated from the high-harmonic generation process can be used to observe element-selective femtosecond-to-attosecond magnetization dynamics of magnetic materials. Using the transverse magneto-optic Kerr effect, we measured an asymmetry of reflectivity in a Permalloy film of up to 6{\%} around the M absorption edges of Fe (54eV) and Ni (67eV). Furthermore, we observed an ultrafast demagnetization of the permalloy film within 250 fs after hearting up by a femtosecond pulse. [Preview Abstract] |
Friday, October 23, 2009 2:22PM - 2:34PM |
B4.00002: A High Bandwidth Optically Pumped Atomic Magnetometer Ricardo Jimenez-Martinez, Clark W. Griffith, Svenja Knappe, John Kitching The measurement of magnetic fields has proved to be relevant in many realms of basic and applied science. Among the different techniques to measure magnetic fields, that of optically pumped atomic magnetometers has experienced considerable attention recently. This interest stems from the development of atomic magnetometers that achieve sensitivities in the sub-femto Tesla range, and the development of techniques that enable highly miniaturized, compact, with low-power consumption magnetometers. The sensitivity and bandwidth of atomic magnetometers is set by their spin coherence time, which in most magnetometers is limited by atomic collisions. Better sensitivities are achieved by suppressing the spin decoherence introduced by atomic collisions, but at a cost of lower bandwidth. For certain applications, a magnetometer with a high bandwidth is useful. Here we present a technique to achieve high bandwidth while preserving high sensitivity. We support the technique with table-top measurements showing that a bandwidth of 10 KHz and sensitivity of 10 pT$_{rms}$/(Hz)$^{1/2}$ can be achieved in a compact device. We also highlight the current development of a miniature atomic magnetometer based on this technique. [Preview Abstract] |
Friday, October 23, 2009 2:34PM - 2:46PM |
B4.00003: Effects of Seed Layers on Ferromagnetic Resonance Linewidths of Fe$_{65}$Co$_{35}$ Thin Films Lei Lu, Ke Sun, Mingzhong Wu, Jared Young, Christoph Mathieu, Matthew Hadley Because of their high saturation magnetization and low coercivity, FeCo thin films have promising applications in both magnetic recording heads and sensors. In light of the applications in recording heads, there is a critical need for the understanding of high-frequency magnetic losses in FeCo thin films. This need is critical because the losses in these films can substantially affect the dynamics of magnetization reversal. This presentation reports for the first time the effect of seed layers on the ferromagnetic resonance (FMR) linewidth of Fe$_{65}$Co$_{35}$ thin films. Six 100 nm-thick films were prepared under the exact same conditions but on different types of seed layers. The FMR measurements were conducted over 8.5-17.5 GHz. The measurements show that the type of seed layer strongly affects both the level and frequency dependence of the FMR linewidth of the films. The results demonstrate the feasibility of the tuning of microwave losses in FeCo films through the use of different seed layers. [Preview Abstract] |
Friday, October 23, 2009 2:46PM - 2:58PM |
B4.00004: Growth of High-Quality Yttrium Iron Garnet Thin Films on Metallic Thin Layers Yiyan Sun, Young-Yeal Song, Mingzhong Wu Yttrium iron garnet (YIG) is one type of ferrite materials that has the lowest loss at microwave frequencies. One typically grows YIG on gadolinium gallium garnet (GGG) substrates, and this is typical mainly because of the perfect matching between the YIG and GGG lattice constants. For applications in monolithic devices, however, one needs to grow YIG films on metallic conductors or electrodes. This presentation reports the deposition of YIG thin films on metallic thin layers and the optimization of the deposition procedures. The metallic and YIG films were deposited by pulsed laser deposition and magnetron sputtering techniques and were characterized by scanning electron microscopy, x-ray diffraction, and ferromagnetic resonance measurements. The work shows rather clearly the critical roles of the selection of metallic materials, the thickness of the metallic layers, the deposition temperature, and the use of buffer layers on the deposition of high-quality YIG films. [Preview Abstract] |
Friday, October 23, 2009 2:58PM - 3:10PM |
B4.00005: Vortex phase diagram for films of type-I Ginzburg-Landau superconductors Mark Sweeney, Martin Gelfand It has been known since the work of Tinkham, Maki, and Pearl in the early 1960's that a thin film of type-I material in a perpendicular field supports a triangular vortex lattice below the upper critical field $H_{c2}$. What happens as film thickness is increased? This was addressed in the vicinity of $H_{c2}$ using linearized Ginzburg-Landau theory, first by Lasher and more completely by Callaway. The vortex phase diagram is remarkably rich. We have made progress on this question within the full G-L theory, following an approach widely applied by Brandt (iteratively solving the G-L equations in a space of trial functions). We find that Brandt's proposed form for the magnetic field in thin-film geometry leads to some unphysical results and have devised an alternative. Our calculations precisely locate phase boundaries between triangular, square, and rectangular vortex arrays as a function of film thickness and magnetic field. They are consistent with a simple picture of vortices which repel near the film surfaces but attract away from them. [Preview Abstract] |
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