Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session Y43: New Techniques and Applications |
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Sponsoring Units: GMAG Chair: Sam Lofland, Rowan University Room: LACC 150C |
Friday, March 25, 2005 11:15AM - 11:27AM |
Y43.00001: Enhanced Magnetostrictively Transduced SAW Devices - Measurements \& Applications Noble C. Woo, Jonathan R. Petrie, R. Bruce van Dover Surface acoustic wave (SAW) transducers can be made with magnetic materials using magnetostriction as a means of electromechanical coupling. Unlike conventional piezoelectrically transduced SAW devices, the magnetically transduced SAWs do not require an exotic single-crystal substrate or high temperature processing, and therefore may be easily integrated into Si-based integrated circuits. These devices have many potential applications, biosensors being one of the most promising. When the substrate between a transmitter and a detector transducer is functionalized with specific bio-receptors, a binding event will affect propagation of the SAW wave that can be detected with simple electronics. In previous MTSAW devices, the magnetomechanical coupling was found to be poor, resulting in insufficient signal amplitude. To obtain better performance, we are studying the use of alternative magnetostrictive materials including an amorphous CoFeTaZr alloy, CoNbZr, and compositions in the Terfernol family (TbFe2, etc.). We are using combinatorial materials science (continuous composition spread approach) to identify optimum alloy compositions. The devices are also being redesigned to yield better performance. [Preview Abstract] |
Friday, March 25, 2005 11:27AM - 11:39AM |
Y43.00002: Permeability and Permittivity Spectra of Ferromagnetic Composites at High Frequencies Xiaokai Zhang, Erik Pearson, Karl Unruh, John Xiao Composites with submicron and nanometer-sized ferromagnetic particles embedded in a dielectric matrix are very promising for a variety of high frequency applications. In particular, these materials offer the potential for exhibiting a high permeability and permittivity, as well as low power losses at operating frequencies. In order to study the effect of the size, shape, and volume fraction of the ferromagnetic component on the microwave properties of these composites, we have prepared a series of samples with varying particle sizes, shapes, and volume ratios in a polymeric matrix. The magnetic and dielectric properties of these samples have been measured in the frequency range from 100 kHz to 18 GHz and compared with the effective medium theory. [Preview Abstract] |
Friday, March 25, 2005 11:39AM - 11:51AM |
Y43.00003: Magnetic anisotropy probed by momentum-resolved EELS Yasuo Ito, Yoshie Murooka, Russell Cook, Michel Van Veenendaal, Nanda Menon, Dean Miller We present an investigation of the temperature induced MLD in microcrystalline antiferromagnetic $\alpha $-Fe$_{2}$O$_{3}$ (hematite) particles, using the STEM-based momentum-resolved EELS [1] with a nanometer-scale electron probe in a 120kV TEM/STEM with the energy resolution lower than 0.7 eV. The focused incident beam was parallel to the c-axis of the (001) oriented microcrystalline. The difference between spectra obtained below and above 263K agrees with the calculated MLD spectrum based on the atomic multiplet calculation for the octahedrally coordinated Fe$^{3+}$ ion in $\alpha $-Fe$_{2}$O$_{3}$. The present result is also consistent with the result obtained by the synchrotron X- ray MLD experiment on a single crystal $\alpha $-Fe$_{2}$O$_{3}$ [2]. [1] J. Yuan, N.K. Menon, J. Appl. Phys. 81, (1997) 5087 [2] P. Kuiper et al., Phys. Rev. Lett. 70 (1993), 1549. [3] This work is supported by the US Department of Education, State of Illinois under HECA, NIU URA program, and work at Argonne, carried out in the Electron Microscopy Center, is supported by the U.S. Department of Energy, Basic Energy Sciences-Materials Sciences, under Contract {\#}W-31-109-ENG-38. [Preview Abstract] |
Friday, March 25, 2005 11:51AM - 12:03PM |
Y43.00004: Neutron Diffuse Reflectometry of Magnetic Thin Films with a 3He Analyzer Wangchun Chen, Kevin O'Donovan, Julie Borchers, Philippe Mangin, Charles Majkrzak, Thomas Gentile Polarized neutron reflectometry (PNR) is a powerful probe that characterizes the magnetization depth profile and magnetic domains in magnetic thin films. Although the conventionally used supermirrors are well-matched for specular PNR, they have limited angular acceptance and hence are impractical for complete characterization of the magnetic off-specular scattering where polarization analysis for diffusely reflected neutrons is required. Polarized $^{3}$He gas, produced by optical pumping, can be used to polarize or analyze neutron beams because of the strong spin dependence of the neutron absorption cross section for $^{3}$He. Here we report efficient polarization analysis of diffusely reflected neutrons in a reflectometry geometry using a polarized $^{3}$He analyzer in conjunction with a position-sensitive detector (PSD). We obtained spin-resolved two-dimensional Q$_{x}$-Q$_{z}$ reciprocal space maps for a patterned array of Co antidots in both the saturated and the demagnetized states. The preliminary results for a patterned amorphous bilayer, Gd$_{40}$Fe$_{60}$/ Tb$_{55}$Fe$_{45}$, measured with a $^{3}$He analyzer and a PSD will also be discussed. Using the spin exchange optical pumping method we have achieved record high $^{3}$He polarizations of 76{\%} on the neutron beam line where we measured an initial analyzing efficiency of 0.97 and a neutron transmission for the desired spin state of 0.45. [Preview Abstract] |
Friday, March 25, 2005 12:03PM - 12:15PM |
Y43.00005: Lithographically defined microdisks as alternative magnetic carriers for biomedical applications V. Novosad, F.Y. Fradin, K. Buchanan, K. Yu. Guslienko, V. Yefremenko, S.D. Bader, A.J. Rosengart, S.G. Guy Magnetic particles can be used as a transduction mechanism for target-directed delivery, manipulation, detection and functional control of attached single bio-molecules or cells. Here we will demonstrate how thin film growth techniques combined with traditional mask-transfer lithography can offer a new concept of magnetic nanoparticles with superior properties for bio-medical applications. The experimental and micromagnetic data for small (from hundred nanometers to few microns) microdisks will be reported. The microdisks have zero remanence due to formation of magnetic vortices in each particle, which results in independent behavior of the assembly of disks, e.g. no agglomeration. A very high Ms (up to 20 kOe) can be achieved~by applying relatively small magnetic fields. Furthermore, the static and dynamic properties of the microdisks can be tailored by choosing the appropriate geometrical aspect-ratio. We will also demonstrate that the resonant collective behavior of spins offers additional possibilities for detection by measurement of the reflected complex impedance of a coplanar micro-waveguide.~ [Preview Abstract] |
Friday, March 25, 2005 12:15PM - 12:27PM |
Y43.00006: Scanning element-specific magnetic microscopy at low temperatures Andrew Cady, D. Haskel, J. C. Lang, G. Srajer, P. Chupas, R. Osborn, J. F. Mitchell, S. Park, S-W. Cheong We have developed a low-temperature element-specific magnetic microscopy tool at beamline 4-ID-D at the Advanced Photon Source. The setup provides a means to measure localized ($\sim$1 sq. micron) magnetic behavior in materials at low temperature ($>$10K) under a moderate applied field ($<$0.8T). We demonstrate the potential of this apparatus by presenting results from two experiments. The first experiment shows the technique’s ability to measure paramagnetic-to-ferromagnetic transition temperatures in micron sized regions of a sample and correlate them with small chemical inhomogeneities. The second experimental result illustrates how the technique can be used to correlate magnetic and chemical domains in a multiferroic system. Work at the Advanced Photon Source was supported by the DOE, Office of Basic Sciences, under contract no. W-31-109-Eng-38. [Preview Abstract] |
Friday, March 25, 2005 12:27PM - 12:39PM |
Y43.00007: Ferromagnetic Resonance Force Microscopy (FMRFM): Magnetostatic modes in the presence of a localized tip field Radovan Urban, Alexander Putilin, Philip Wigen, Michael Cross, Michael Roukes Magnetostatic modes of Yttrium Iron Garnet (YIG) films have been investigated by ferromagnetic resonance force microscopy (FMRFM). A probe magnet on the tip of a compliant cantilever introduces inhomogeneity in the internal field of the YIG sample. The local variation of this internal field creates a perturbation upon the sample's magnetostatic modes analogous to either a potential barrier or well, depending on the mutual orientation of the external dc and the tip field. For antiparallel orientation of the external and tip field, localization of the magnetostatic modes can be observed. This allows one to extract local magnetic properties of ferromagnetic samples in spite of the strong spin-spin interaction. The lateral resolution of localized modes scales with size of the probe magnet. Data from our experiments is in excellent agreement with the theoretical predictions based upon the Landau-Lifshitz-Gilbert equation of motion and Maxwell's equations. [Preview Abstract] |
Friday, March 25, 2005 12:39PM - 12:51PM |
Y43.00008: Scanning Hall Probe Microscopy (SHPM) using Quartz Crystal AFM Feedback Munir Dede, Koray Urkmen, Ahmet Oral Scanning Hall Probe Microscopy (SHPM)[1] is a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations such as ferromagnetic domains with high spatial and magnetic field resolution of $\sim $50nm {\&} 7mG/(Hz)$^{0.5}$ at room temperature. In the SHPM technique, Scanning Tunneling Microscope(STM)[1] or Atomic Force Microscope(AFM)[2] feedback is usually used for bringing the Hall sensor into close proximity of the sample. In the latter, the Hall probe has to be integrated with an AFM cantilever in a complicated microfabrication process. In this work, we have eliminated the difficult cantilever-Hall probe integration process; a Hall sensor is simply glued at the end of a 32,768 Hz Quartz crystal, which is used as force sensor. The sensor assembly is dithered at the resonance frequency and the quartz force sensor output is detected with a Lock-in. SHPM electronics is modified to detect AFM topography and the phase, along with the magnetic field image. NIST MIRS ( Hard Disk ) sample is imaged with the Quartz Crystal AFM feedback and the performance is found to be comparable with the SHPM using STM feedback. Quartz Crystal AFM feedback offers a very simple sensor fabrication and operation in SHPM. This method eliminates the necessity of conducting samples for SHPM. [1] A. Oral \textit{et. al.} Appl. Phys. Lett., 69, 1324 (1996) [2] A.J. Brook \textit{et. al.} Appl. Phys. Lett. 82, 3538 (2003) [Preview Abstract] |
Friday, March 25, 2005 12:51PM - 1:03PM |
Y43.00009: A study of the magnetic hysteresis of a single magnetic element using a sensitive microcantilever torque magnetometer L. Gao, L. Yuan, K.H.P. Kim, S.H. Liou, M.D. Chabot, D.H. Min, J.M. Moreland A sensitive microcantilever torque magnetometer (MTM) has been developed for measuring the magnetic properties of nanomagnets. The sensitivity of the technique at room temperature in air was demonstrated by the successful measurement of the magnetization switching of a single micronmeter sized Ni$_{80}$Fe$_{20 }$element. The permalloy dot has a size of 1.5 $\mu $m in diameter and 30 nm in thickness with a moment of 5.5 $\times $ 10$^{-11}$ emu. The sensitivity of our current MTM instrument can be estimated as 10$^{-12}$ emu, which is about three orders better than commercial SQUID. The hysteresis loop indicates that the switching process of the element is dominated by the domain wall propagation through the element gradually. [Preview Abstract] |
Friday, March 25, 2005 1:03PM - 1:15PM |
Y43.00010: The Born Oppenheimer-Potential for the Hydrogen Bond in the H5O2+ Complex: Comparison of Theories and Experiment Nina Verdal, Bruce Hudson, George Reiter The Born-Oppenheimer potential surface for motion of the central H atom in the hydrogen bond in the H$_{5}$O$_{2}^{+}$ ion is of considerable interest. This quantity has been elusive experimentally and computations are of unknown reliability. By measuring the momentum distribution of the protons in the centrosymmetric aquonium perchlorate, H$_{5}$O$_{2}^{+}$ ClO$_{4}^{-}$, and subtracting the ice-like contribution from the non-hydrogen bonded protons, we are able to measure the momentum distribution of the proton in the bond. This distribution is calculated for several ab-initio treatments of the potential surface and compared with the measurements as a means of distinguishing between these methods. [Preview Abstract] |
Friday, March 25, 2005 1:15PM - 1:27PM |
Y43.00011: Ordered and Disordered Magnetic States in Mott insulators: Insights from Spectral Density Functional Theory Quan Yin, Sergej Savrasov, Gabriel Kotliar Self-consistent many body + electronic structure calculations using dynamical mean field based spectral density functional method are presented to study various magnetic states in several Mott-Hubbard insulators such as classical transition metal oxides MnO, FeO, CoO, NiO, as well as FeS. Solution of the Anderson impurity problem in these strongly correlated systems will be approximated by using the Hubbard I method. Comparison will be made for the electronic spectral functions and magnetic moments in both ordered and local moment regimes. The results will be contrasted to less rigorous LDA+U calculations. Prospects for theoretical predictions of the Neel temperatures within this method will be discussed. [Preview Abstract] |
Friday, March 25, 2005 1:27PM - 1:39PM |
Y43.00012: Renormalization group method for weakly-coupled quantum chains: application to the spin one-half Heisenberg model Samuel Moukouri The Kato-Bloch perturbation formalism is used to present a density-matrix renormalization-group (DMRG) method for strongly anisotropic two-dimensional systems. This method is used to study Heisenberg chains weakly coupled by the transverse couplings $J_{\perp}$ and $J_{d}$ (along the diagonals). An extensive comparison of the renormalization group and quantum Monte Carlo results for parameters where the simulations by the latter method are possible shows a very good agreement between the two methods. It is found, by analyzing ground state energies and spin-spin correlation functions, that there is a transition between two ordered magnetic states. When $J_{d}/J_ {\perp} \alt 0.5$, the ground state displays a N\'eel order. When $J_{d}/J_{\perp} \agt 0.5$, a collinear magnetic ground state in which interchain spin correlations are ferromagnetic becomes stable. In the vicinity of the transition point, $J_ {d}/J_{\perp} \approx 0.5$, the ground state is disordered. But, the nature of this disordered ground state is unclear. While the numerical data seem to show that the chains are disconnected, the possibility of a genuine disordered two- dimensional state, hidden by finite size effects, cannot be excluded. [Preview Abstract] |
Friday, March 25, 2005 1:39PM - 1:51PM |
Y43.00013: Method of measuring anhysteretic magnetization and magnetostriction in ferromagnetic thin films Peter Finkel, Edward Garrity We have developed a new method of the stress dependant anhysteretic magnetization measurements in a thin--film ferromagnetic materials. This is achieved by combining conventional vibrating sample magnetometer with the specially designed loading fixture allowing to apply uniaxial stresses on thin film and wires. The anhysteretic magnetization is obtained by ac demagnetization of the sample and measuring the subsequent magnetization at a given dc magnetic field. Also we have developed a contactless method for determining uniaxial stress in thin anisotropic ferromagnetic samples based on monitoring velocity of a flexural wave using time of flight measurements. The method has been demonstrated for membrane thickness down to 100$\mu $m and stresses up to 1 GPa. Estimated accuracy of this method is better than 0.2{\%}. [Preview Abstract] |
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Y43.00014: Sensitive Measurement of Parallel and Transverse Susceptibility by Alternating Gradient Magnetometry Mladen Barbic, Mary Brady Reversible susceptibility tensor measurements reveal important information about the switching fields and anisotropies of magnetic materials. We show that a simple reconfiguration of an alternating gradient magnetometer can be used to measure both reversible parallel and transverse susceptibilities with high sensitivity. It is demonstrated that positioning the sample off-axis with respect to the magnetometer gradient field coils results in a signal at twice the frequency of the gradient field that is directly proportional to the reversible susceptibility. Offsetting the sample along the x-axis results in a sensor signal proportional to the reversible parallel susceptibility, while rotating the sample holder by 90 degrees and offsetting it along the y-axis results in a sensor signal proportional to the reversible transverse susceptibility. Examples of reversible parallel and transverse susceptibility measurements of aligned nanoparticle systems will be demonstrated. [Preview Abstract] |
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