Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 58, Number 12
Friday–Saturday, October 18–19, 2013; Denver, Colorado
Session I2: Condensed Matter III: Magnetics |
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Chair: Lincoln Carr, Colorado School of Mines Room: 281 |
Saturday, October 19, 2013 8:00AM - 8:24AM |
I2.00001: Yttrium Iron Garnet Nano Films for Spintronics Applications Invited Speaker: Mingzhong Wu Magnetization precession in yttrium iron garnet (YIG) damps slower than in any other known magnetic materials. This fact gives rise to the recent birth of a new paradigm in the discipline of spintronics -- ``spintronics using yttrium iron garnets.'' This presentation will touch on several important topics related to YIG spintronics. The first part will demonstrate the feasibility of the use of pulsed laser deposition and magnetron sputtering to grow low-damping, nanometer-thick YIG films. The second part will present the determination of efficiency of spin angular momentum transfer across YIG/normal metal interfaces. The last part of the presentation will report on the impacts of the magnetic proximity effect on spin pumping in YIG/Pt heterostructures.\\[4pt] In collaboration with Yiyan Sun, Tao Liu, Houchen Chang, Zihui Wang, Michael Kabatek, William Schneider, Department of Physics, Colorado State University; B. Kardasz, C. Burrowes, E. Montoya, B. Heinrich, Department of Physics, Simon Fraser University; and Suzanne Velthuis, Vincent Vlaminck, Helmut Schulthei{\ss}, Axel Hoffmann, Materials Science Division, Argonne National Laboratory. [Preview Abstract] |
Saturday, October 19, 2013 8:24AM - 8:36AM |
I2.00002: Ferromagnetic Resonance in CoFeB Ultrathin Films with Perpendicular Anisotropy David Ellsworth, Lei Lu, Mingzhong Wu, Ding-Shuo Wang, Chih-Huang Lai Magnetic ultrathin films with perpendicular anisotropy have potential applications in high-density, fast-switching magnetic memories. This presentation reports on ferromagnetic resonance (FMR) in CoFeB films which are only 1 nm thick and have strong perpendicular magneto-crystalline anisotropy. The samples were a multi-layered structure of Si/SiO2/Pd(3nm)/CoFeB(1nm)/MgO(1.6nm)/Pd(3nm). The FMR measurements were carried out by placing the film sample on a co-planar waveguide (CPW), magnetizing the film with an out-of-plane magnetic field, and measuring the transmission coefficients of the film/CPW structure with a vector network analyzer. The measurements were conducted over a frequency range of 10-33 GHz. The fitting of the measured FMR field vs. frequency responses with the Kittel equation yielded effective anisotropy fields that were close to the values obtained from the hysteresis loop measurements of the films. The linear fitting of the FMR linewidth vs. frequency responses gave rise to an effective Gilbert damping constant range of 0.01-0.02. The fitting also indicated a strong contribution (200-500 Oe) to the FMR linewidth from long-range film inhomogeneity. [Preview Abstract] |
Saturday, October 19, 2013 8:36AM - 8:48AM |
I2.00003: Structural and magnetic characterizations of organically prepared Fe$_{3}$O$_{4}$ nanoparticles Karine Chesnel, Matea Trevino, Yanping Cai, Jared Hanckock, Roger Harrison Magnetite (Fe3O4) particles exhibit a superparamagnetic behavior when their size is in nanometer scale. Because of their small sizes, their ability to be manipulated by a magnetic field, and their compatibility with the human body, Fe3O4 nanoparticles can potentially be used in a wide range of applications in the medical field. Our goal is to investigate the magnetic properties in self-assemblies of such nanoparticles. We fabricate our Fe3O4 nanoparticle and characterize them by magnetometry measurements. We have investigated different preparation methods: an inorganic route, mixing salts or mixing solution, and an organic route.. XRD measurements show that the different methods lead to different sizes of particles, ranging from 5 nm to 50 nm in size. It also shows that the organic method leads to smaller particles of about 5nm, with a better size control. Magnetometry FC/ZFC measurements show a blocking temperature in the range of 100K to 200K. The smaller particles with better size control are then used to form a thin film. The particles are deposited on a substrate and just tend to form a lattice, here hexagonal lattice. The goal is to achieve one monolayer. The film is then used for synchrotron X-ray XMCD and XRMS measurements. [Preview Abstract] |
Saturday, October 19, 2013 8:48AM - 9:00AM |
I2.00004: Magneto-optical Kerr effect hysteresis measurements of pound-key-like magnetic nanostructures Lin Li, Martin Asmat, Brian Shaw, Arabinda Haldar, Kristen Buchanan The magnetic antivortex (AV) state is a topological configuration that is expected to exhibit interesting physical behavior and it may also be useful for applications. Recent work showed that magnetic antivortices can be created in pound-key-like nanostructures via a two-step magnetic field procedure [1]. In this procedure, magnetic hysteresis measurements are important to predict the field values at which the AV's will form. The Magneto-Optical Kerr Effect (MOKE) is widely used to make magnetic hysteresis measurements, especially for magnetic nanostructures since measurements can be made on individual structures or small arrays. MOKE measurements were made on a series of micron-sized pound-key-like structures made of Permalloy to examine how the reversal process and critical fields depend on the details of the structure shape and size. Hysteresis loops were obtained with a high signal-noise ratio even though the amount of magnetic material and consequently the Kerr rotation angle were small (less than 0.02 mrad). Subsequent magnetic force microscopy imaging of the structures showed successful AV formation at the fields predicted from the MOKE measurements.\\[4pt] [1] Haldar and Buchanan, Appl. Phys. Lett. 102, 112401 (2013). [Preview Abstract] |
Saturday, October 19, 2013 9:00AM - 9:12AM |
I2.00005: Detection of Magnetic Antivortices with Magnetic Force Microscopy Brian Shaw, Martin Asmat-Uceda, Lin Li, Arabinda Haldar, Kristen Buchanan Magnetic antivortices (AV's) are uniquely shaped domain pattern that involve magnetic moments that sweep inwards from two opposing directions, e.g., the top and bottom, then outwards to the left and right, with a central out-of-plane core that is only $\sim$10 nm in diameter at the intersection. AV's possess interesting and potentially useful properties but they are metastable and are thus difficult to create reliably. We recently showed that AV's will form in pound-key-shaped structures made from Permalloy that are on the order of tens of microns in size. In this talk, I will discuss measurements of the statistics of the AV formation several different variations on this design. Arrays that contained 625 nominally identical structures were magnetized using fields at and near the coercive field of the structures as determined from hysteresis measurements, and then the arrays were imaged using magnetic force microscopy (MFM) to identify the magnetic states. The AV's can be easily identified in MFM images by their distinct hourglass shape. For each structure design at least three areas, each containing 25 structures, were imaged to determine the success rate of the AV formation. Our results show that the details of the geometry are important and confirm that the hysteresis measurements can be used to select the best fields for a given structure design. [Preview Abstract] |
Saturday, October 19, 2013 9:12AM - 9:24AM |
I2.00006: Magnetic order and fluctuation of Fe3O4 nanoparticles Yanping Cai, Karine Chesnel, Matea Trevino, Andrew Westover, Roger Harrison, Alexander Reid, Andreas Scherz Magnetite (Fe$_{3}$O$_{4})$ nanoparticles tend to self-assemble when they are deposited on a substrate. Our goal is to understand the magnetic order and magnetic interactions between the particles, when they are self-assembled. After bulk structural and magnetic characterizations, we have been studying our Fe$_{3}$O$_{4}$ nanoparticles by using X-ray Magnetic Circular Dichroism (XMCD) as well as X-ray Resonant Magnetic Scattering (XRMS) at synchrotron radiation facilities. Both techniques utilize the interaction between magnetic spins in the material and polarized light. The XMCD can identify the L$_{2}$ and L$_{3}$ edges and gives information about the average magnetization in the material. We set our X-ray energy at the L3 edge and collect the XRMS scattering pattern. The XRMS scattering pattern shows information about the magnetic order and magnetic fluctuations in the nanoparticles assembly.~By studying the profile of the XRMS patterns, we~try to extract the magnetic signal from the charge signal, and learn about the magnetic order between the nanoparticles. We also utilize the coherence of the X-ray light and apply a correlation spectroscopy technique to learn about magnetic fluctuations. [Preview Abstract] |
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