Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session W16: Focus Session: Biomagnetics, Magneto-Optics, and Ultrafast Effects |
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Sponsoring Units: GMAG DMP Chair: Weigang Wang, University of Arizona Room: 318 |
Thursday, March 21, 2013 2:30PM - 3:06PM |
W16.00001: GMAG PhD Dissertation Research Award Talk: Dynamic Magnetic Traps for Particle Self-Assembly and Lab-on-Chip Applications Invited Speaker: Aaron Chen Micro-patterned Permalloy thin films serve as an excellent means to architect the spatial profile of magnetic fields with the tunable, high gradients required to manipulate objects with weak induced magnetic moments. In this presentation, I will highlight two projects carried out during my PhD studies. These findings demonstrate the functionalities achieved through carefully designed patterns of different sizes and shapes (e.g. circular, triangular, octagonal profiles): (i) By tuning a precessing magnetic field in conjunction with such Permalloy patterns, microsphere (i.e. dipole) cluster structures ranging from closely packed to frustrated and to plum-pudding-like planar lattices are stabilized. Such self-assembly of components at the micro to nanometer range not only support a rich variety of physical phenomena, but also have applications, for example, as filters or force probes and field-tunable photonic crystals. (ii) Mobile magnetic trap arrays consisting of Permalloy disks have enabled rapid transport of magnetic beads or immunomagnetically labeled cells across surfaces. Integration of these arrays with microfluidic droplet technology allows separation of labeled cells and their subsequent encapsulation into picoliter-sized droplets. The droplets serve as isolated containers for individual cells to be probed without cross-contamination. The separation-encapsulation function could become a critical component in point-of-care single-cell analysis platforms. [Preview Abstract] |
Thursday, March 21, 2013 3:06PM - 3:18PM |
W16.00002: Magnetic multicomponent nanoparticles Cu$_{x}$Mn$_{1-x}$Fe$_{2}$O$_{4}$ for biomedical applications Nurcan Dogan Magnetic nanoparticles (NPs) are increasingly important in many biomedical applications, such as drug delivery, hyperthermia, and magnetic resonance imaging (MRI) contrast enhancement. In this multicomponent nanoparticles Cu$_{x}$Mn$_{1-x}$Fe$_{2}$O$_{4}$ (CuMnF), x$=$ 0, 0.6, 1, were prepared by hydrothermal synthesis, sol-gel and solid state methods. To build the most effective magnetic nanoparticle systems for various biomedical applications, particle characteristics including size, surface chemistry, magnetic properties and toxicity have to be fully investigated. In this work, effects of production methods of magnetic nanoparticles for the bio-medical applications are discussed. X-ray powder diffractometry (XRD), scanning electron microscopy (SEM) and vibrating scanning magnetometer (VSM) were used to characterize the structural, morphological and magnetic properties. The particle size of samples is measured by Malvern Instruments Zeta Sizer Nano-ZS instrument. The temperature dependence of field cooled (FC) magnetization of all Cu$_{x}$Mn$_{1-x}$Fe$_{2}$O$_{4}$ samples have been shown here. The data were recorded under 1k Oe and 100 Oe magnetic fields for different ratio. [Preview Abstract] |
Thursday, March 21, 2013 3:18PM - 3:30PM |
W16.00003: Detection of low-concentration superparamagnetic nanoparticles using a functional biosensor based on magneto-impedance technology Jagannath Devkota, Alejandro Ruiz, Pritish Mukherjee, Hariharan Srikanth, Manh-Huong Phan, Chunyan Wang, Subhra Mohapatra Improving the sensitivity of existing magnetic biosensors for detection of magnetic nanoparticles as biomarkers in biological systems is an important and challenging task. Here we demonstrate the possibility of combining the magneto-resistance (MR), magneto-reactance (MX), and magneto-impedance (MI) effects to develop a functional magnetic biosensor with tunable and enhanced sensitivity. A systematic study of the 7 nm Fe$_{\mathrm{3}}$O$_{\mathrm{4\thinspace }}$nanoparticle concentration dependence of MR, MX, and MI ratios of a soft ferromagnetic amorphous ribbon shows that these ratios first increase sharply with increase in particle concentration (0 - 124 nM) and then become unchanged for higher concentrations ($>$124 nM). This points to the sensitivity and limit of the detection of the biosensor. The MX-based biosensor shows the highest sensitivity. With this sensor, 2.1$\times $10$^{\mathrm{11}}$ 7 nm Fe$_{\mathrm{3}}$O$_{\mathrm{4}}$ nanoparticles can be detected over a detection area of 2.0$\times $10$^{\mathrm{5\thinspace }}\mu $m$^{\mathrm{2}}$, which is comparable to a SQUID biosensor that detects the presence of 1$\times $10$^{\mathrm{8\thinspace }}$11 nm Fe$_{\mathrm{3}}$O$_{\mathrm{4}}$ nanoparticles over a detection area of 6.8$\times $10$^{\mathrm{4\thinspace }}\mu $m$^{\mathrm{2}}$. [Preview Abstract] |
Thursday, March 21, 2013 3:30PM - 3:42PM |
W16.00004: Characterization of magnetic nanoparticles using Magnetic Hyperthermia System (MHS) for the application in cancer treatment M.E. Sadat, Ronak Patel, David B. Mast, Donglu Shi, Sergey L. Bud'ko, Jiaming Zhang, Hong Xu In this study, the heating profiles of various concentrations of three Fe$_{3}$O$_{4}$ magnetic nanoparticle systems were measured when the nanoparticles were exposed to alternating magnetic fields in a RF Magnetic Hyperthermia System. The Fe$_{3}$O$_{4}$ core nanoparticles of each system were approximately 10nm in diameter, but each system had different nanoparticle configurations and surface modifications. The heating profiles were used to investigate the dominant heating mechanism, the heat transfer into the surrounding fluid, and the overall effectiveness of each nanoparticle system for possible use in hyperthermia cancer treatments. Magnetization measurements showed that all samples were superparamagnetic in nature with almost zero retentivity and coercivity. For all samples, the saturation magnetization was observed to increase linearly with increasing concentration of Fe$_{3}$O$_{4}$. Five different concentrations of the three Fe$_{3}$O$_{4}$ nanoparticle samples were exposed to a 13.56 MHz alternating magnetic field with an amplitude of 4500 A/m, while the solution temperature was measured as a function of time using an optical fiber temperature probe. A correlation was observed between the heating rate, the initial susceptibility, and the type of surface modification of the Fe$_{3}$O$_{4}$ nanoparticles. [Preview Abstract] |
Thursday, March 21, 2013 3:42PM - 3:54PM |
W16.00005: Magnetization measurements of magnetic fluids Z. Boekelheide, C. L. Dennis Magnetic fluids are used for damping in vehicle suspensions, as MRI contrast agents, heat transfer materials, and even in art installations. Most of these applications benefit from high quality magnetic characterization. Techniques for measuring magnetization ($M$) of materials, such as vibrating sample magnetometry (VSM), and superconducting quantum interference device (SQUID) magnetometry, are well-developed for small solid samples such as bulk crystals and thin films. This presentation discusses special issues that arise in measurement of fluid samples. First, the effects of the sample vessel must be taken into account. Often, the vessel must be vacuum-tight; care must be taken that the sealing process does not physically change the properties of the fluid. Then, the portion of the signal due to the sample vessel should be subtracted from the total, not a trivial subtraction as the sample vessel has a different geometry from the sample (in contrast to, e.g., a thin film sample and substrate). In addition, the sample must be centered, adding an additional degree of difficulty when the material is fluid and the center position may be a dynamic property. Our results show that incorrect centering can lead to not only incorrect values of $M$, but to a change in the shape of $M(H)$. [Preview Abstract] |
Thursday, March 21, 2013 3:54PM - 4:06PM |
W16.00006: Probing Brownian relaxation in water-glycerol mixtures using magnetic hyperthermia Humeshkar Nemala, Michael Milgie, Anshu Wadehra, Jagdish Thakur, Vaman Naik, Ratna Naik Generation of heat by magnetic nanoparticles in the presence of an external oscillating magnetic field is known as magnetic hyperthermia (MHT). This heat is generated by two mechanisms: the Neel relaxation and Brownian relaxation. While the internal spin relaxation of the nanoparticles known as Neel relaxation is largely dependent on the magnetic properties of the nanoparticles, the physical motion of the particle or the Brownian relaxation is largely dependent on the viscous properties of the carrier liquid. The MHT properties of dextran coated iron oxide nanoparticles have been investigated at a frequency of 400KHz. To understand the influence of Brownian relaxation on heating, we probe the MHT properties of these ferrofluids in water-glycerol mixtures of varying viscosities. The heat generation is quantified using the specific absorption rate (SAR) and its maximum at a particular temperature is discussed with reference to the viscosity. [Preview Abstract] |
Thursday, March 21, 2013 4:06PM - 4:18PM |
W16.00007: ABSTRACT WITHDRAWN |
Thursday, March 21, 2013 4:18PM - 4:30PM |
W16.00008: Propagation of Electromagnetic Waves in 3D Opal-based Magnetophotonic Crystals Martha Pardavi-Horvath, Galina S. Makeeva, Oleg A. Golovanov, Anatolii B. Rinkevich Opals, a class of self-organized 3D nanostructures, are typical representatives of photonic bandgap structures. The voids inside of the opal structure of close packed SiO$_{2}$ spheres can be infiltrated by a magnetic material, creating magnetically tunable magnetophotonic crystals with interesting and potentially useful properties at GHz and THz frequencies. The propagation of electromagnetic waves at microwave frequencies was investigated numerically in SiO$_{2}$ opal based magnetic nanostructures, using rigorous mathematical models to solve Maxwell's equations complemented by the Landau-Lifshitz equation with electrodynamic boundary conditions. The numerical approach is based on Galerkin's projection method using the decomposition algorithm on autonomous blocks with Floquet channels. The opal structure consists of SiO$_{2}$ nanospheres, with inter-sphere voids infiltrated with nanoparticles of Ni-Zn ferrites. Both the opal matrix and the ferrite are assumed to be lossy. A model, taking into account the real structure of the ferrite particles in the opal's voids was developed to simulate the measured FMR lineshape of the ferrite infiltrated opal. The numerical technique shows an excellent agreement when applied to model recent experimental data on similar ferrite opals. [Preview Abstract] |
Thursday, March 21, 2013 4:30PM - 4:42PM |
W16.00009: Ultrafast Magnetization Enhancement in Metallic Multilayers Driven by Superdiffusive Spin Current Emrah Turgut, Chan La-O-Vorakiat, Patrik Grychtol, Henry C. Kapteyn, Margaret M. Murnane, Dennis Rudolf, Roman Adam, Claus M. Schneider, Marco Battiato, Pablo Maldonado, Peter M. Oppeneer, Stefan Mathias, Martin Aeschlimann, Justin M. Shaw, Hans T. Nembach, Thomas J. Silva We report on the surprising enhancement in the magnetization of iron in Ni:Fe based multilayer structures following the excitation by an ultrafast laser pulse. Few femtosecond extreme ultraviolet pulses from tabletop high harmonic generation, tuned to the M-edges of Ni and Fe, are used to probe the layer- and element- specific spin dynamics in multilayer structures of Ni/X/Fe, where X is Ru, Ta, W, or Si3N4. We find that both the Ni and Fe moments demagnetize on timescales of 100 fs when excited by an ultrafast optical pulse, for good spin scattering and insulating spacer layers consisting of Ta, W, and Si3N4. However, we also find that the Fe magnetization is enhanced by 16{\%} for Ru spacer layers of 1.7 nm thickness, when the magnetizations of the Fe/Ni layers are initially aligned parallel. Our observations can be explained by a laser-generated superdiffusive spin current between the Ni and Fe layers, whereby a substantial current of majority spins injected into the Fe layer enhances its magnetization. [1] [1] D. Rudolf et. al. Nat. Comm. 3, 1037 (2012) [Preview Abstract] |
Thursday, March 21, 2013 4:42PM - 4:54PM |
W16.00010: A microscopic model for ultrafast remagnetization dynamics Biplab Sanyal, Raghuveer Chimata, Anders Bergman, Lars Bergqvist, Olle Eriksson In this work, we provide a microscopic model for the ultrafast remagnetization of atomic moments already quenched above Stoner-Curie temperature by a strong laser fluence. Combining first principles density functional theory, atomistic spin dynamics utilizing the Landau-Lifshitz-Gilbert equation and a three temperature model, we show the temporal evolution of atomic moments as well as the macroscopic magnetization of bcc Fe and hcp Co covering a broad time scale, ranging from femtoseconds to picoseconds. Our simulations show [1] a variety of complex temporal behavior of the magnetic properties resulting from an interplay between electron, spin and lattice subsystems, which causes an intricate time evolution of the atomic moment, where longitudinal and transversal fluctuations result in a macro spin moment that evolves highly non-linearly.\\[4pt] [1] Raghuveer Chimata, Anders Bergman, Lars Bergqvist, Biplab Sanyal and Olle Eriksson, Phys. Rev. Lett. {\bf 109}, 157201 (2012). [Preview Abstract] |
Thursday, March 21, 2013 4:54PM - 5:06PM |
W16.00011: Current understanding of the laser-induced ultrafast (de)magnetization process Guoping Zhang, Mingqiang Gu, M.S. Si, T.F. George, Xiaoshan Wu The laser-induced ultrafast (de)magnetization process in ferromagnets is complex. There are several theories available [1], but none of these is satisfactory. In this talk, we first review several theoretical formalism for femtomagnetism and point out strengths and weaknesses of each theory [2]. In particular, we address issues associated with comparing experimental and theoretical results, which have been very challenging. Our first-principles theory includes electron correlation and electron-phonon effects along with spin-orbit coupling in metals or rare-earth compounds. Some of the newest results are presented, which are expected to tremendously enhance our understanding of the overall (de)magnetization process [3].\\[4pt] [1] G. P. Zhang, G. Lefkidis, W. H\"ubner, and Yihua Bai, J. APPL. PHYS. {\bf 111}, 07C508 (2012).\\[0pt] [2] M. S. Si and G. P. Zhang, AIP ADVANCES {\bf 2}, 012158 (2012).\\[0pt] [3] G. P. Zhang, PHYSICAL REVIEW B {\bf 85}, 224407 (2012). [Preview Abstract] |
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