Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session B30: Focus Session: Nanomagnetic Devices II |
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Kai Liu, University of California, Davis Room: 206B |
Monday, March 2, 2015 11:15AM - 11:27AM |
B30.00001: Micromagnetic Architectures for On-chip Microparticle Transport Minae Ouk, Geoffrey S.D. Beach Superparamagnetic microbeads (SBs) are widely used to capture and manipulate biological entities in a fluid environment. Chip-based magnetic actuation provides a means to transport SBs in lab-on-a-chip devices. This is usually accomplished using the stray field from patterned magnetic microstructures [1], or domain walls in magnetic nanowires [2]. Magnetic anti-dot arrays are particularly attractive due to the high-gradient stray fields from their partial domain wall structures [3]. Here we use a self-assembly method to create magnetic anti-dot arrays in Co films, and describe the motion of SBs across the surface by a rotating field. We find a critical field-rotation frequency beyond which bead motion ceases and a critical threshold for both the in-plane and out-of-plane field components that must be exceeded for bead motion to occur. We show that these field thresholds are bead size dependent, and can thus be used to digitally separate magnetic beads in multi-bead populations. Hence these large-area structures can be used to combine long distance transport with novel functionalities. [1] B. Yellen, et al., Lab Chip, 7, 1681 (2007) [2] E. Rapoport and G. S. D. Beach, APL 100, 082401 (2012) [3] C C Wang, et al., Nanotechnology 17, 1629 (2006) [Preview Abstract] |
Monday, March 2, 2015 11:27AM - 11:39AM |
B30.00002: Parallel Dipole Line System: A Novel Magnetic Trap and High Sensitivity Hall system Oki Gunawan, Yudistira Virgus, Kong Fai Tai A system that could trap cylindrical objects such as semiconductor nanowires provides a route towards self-assembled fabrication of bottom-up nanowire integrated circuit. We show that such a trap can be realized using a simple parallel dipole line (PDL) system which can be experimentally realized using diametrically-magnetized magnets with a diamagnetic rod as the trapped object. This system produces a fascinating 1D camelback potential profile at the center plane and yields a new technique for magnetic susceptibility measurement for the trapped rod. This system also yields a surprising application for a high sensitivity Hall measurement system which plays a decisive role in extracting low carrier mobility in earth abundant kesterite solar cell. [Preview Abstract] |
Monday, March 2, 2015 11:39AM - 11:51AM |
B30.00003: Geometric Constraints on Planar Manipulation of Microparticles via Magnetic Traps C. Pierce, M. Prikockis, R. Sooryakumar Recently, thin film based devices have been developed to trap and transport particles via localized magnetic fields and the associated strong gradients found at domain walls in patterned wires. In scaling up the device performance to achieve greater throughput and finer control over the spatial resolution in maneuvering the particles, it is necessary to understand the constraints imposed by the architecture of the wires. Due to shape anisotropy, ferromagnetic microstructures of Co$_{0.5}$Fe$_{0.5}$ comprising isolated and connected linear segments acquire stable magnetic domain states when magnetized in an external field. The stray fields in the vicinity of the domain walls, when combined with weak external fields ($\sim$ 10 Oe), create sites which controllably attract or repel superparamagnetic micro-particles. The dependence of trap strength on device scale, aspect ratio, geometry and orientation relative to magnetizing field and neighboring sites are investigated through simulation and experiments involving magnetic microparticles of various sizes. Constraints placed on the types of manipulations achievable with this scheme and their implications towards realizing high throughput Lab-on-a-Chip devices will be discussed. [Preview Abstract] |
Monday, March 2, 2015 11:51AM - 12:27PM |
B30.00004: (001) Oriented $L1_{0}$ FeCuPt for Heat-Assisted Magnetic Recording Invited Speaker: Kai Liu High magnetic anisotropy materials are critical to key technologies such as ultrahigh density magnetic recording and permanent magnets. Among them, ordered FePt alloys in the $L$1$_{0}$ phase are particularly sought after, for the emerging heat-assisted magnetic recording (HAMR) media. However, the highly desirable properties are associated with the tetragonal $L$1$_{0}$ phase. Key challenges exist in the high annealing temperature necessary to transform the as-deposited disordered cubic $A$1 phase into the ordered tetragonal$ L$1$_{0}$ phase and the ability to maintain the magnetic easy axis perpendicular to the film. We have achieved (001) oriented $L$1$_{0}$ FeCuPt thin films, with magnetic anisotropy up to 3.6 x 10$^{7}$ erg/cm$^{3}$, using atomic-scale multilayer sputtering and rapid thermal annealing (RTA) at 400 $^{\circ}$C for 10 seconds, which is much more benign compared to earlier studies [1]. The artificial ordering in the multilayer structure and a significant tensile stress exerted by the underlying Si/SiO$_{2}$ during RTA facilitate the formation of (001) oriented $L$1$_{0}$ phase. The $A$1 to $ L$1$_{0}$ phase transformation has been investigated by x-ray diffraction and the first-order reversal curve (FORC) method [2]. The $L$1$_{0}$ ordering takes place via a nucleation-and-growth mode. Traditional x-ray diffraction is not always reliable in generating a true order parameter, due to non-ideal crystallinity of the $A$1 phase in some of the samples. A magnetization-based $L$1$_{0}$ phase fraction is extracted, providing a quantitative measure of the $L$1$_{0}$ phase homogeneity [3]. \\[4pt] [1] D. A. Gilbert, L. W. Wang, T. J. Klemmer, J. U. Thiele, C. H. Lai, and K. Liu, \textit{Appl. Phys. Lett.}, \textbf{102}, 132406, (2013).\\[0pt] [2] D. A. Gilbert, G. T. Zimanyi, R. K. Dumas, M. Winklhofer, A. Gomez, N. Eibagi, J. L. Vicent, and K. Liu, \textit{Sci. Rep}, \textbf{4}, 4204 (2014).\\[0pt] [3] D. A. Gilbert, J. W. Liao, L. W. Wang, J. W. Lau, T. J. Klemmer, J. U. Thiele, C. H. Lai, and K. Liu, \textit{APL Mater}, \textbf{2}, 086106 (2014). [Preview Abstract] |
Monday, March 2, 2015 12:27PM - 12:39PM |
B30.00005: Magnetic anisotropy modified by strain effects in Y$_2$Fe$_{14}$B Yoshihiro Gohda, Zahra Torbatian, Taisuke Ozaki, Shinji Tsuneyuki In exhibiting the coercivity of permanent magnets, magnetocrystalline anisotropy plays an important role. Since itinerant magnetic states are responsible to direct interactions among magnetic sites, d states are expected to be sensitive to lattice strain. In this work, we report strain effects on magnetic properties theoretically studied by first-principles calculations for Y$_2$Fe$_{14}$B, where Y is a prototypical $f^0$ rare-earth element [1]. To analyze the local magnetic anisotropy, we developed a method to decompose the magnetic-anisotropy energy into contribution from each atomic site as well as from couplings among specific atomic orbitals, where the sum rule is satisfied by including indirect off-site contributions in the second-order perturbation. The OpenMX code is used for first-principles calculations. The lattice constants of Y$_2$Fe$_{14}$B are changed from the equilibrium values independently, where we found the uniform compression enhances the perpendicular magnetic anisotropy. Our magnetic-anisotropy decomposition identified dominant magnetic site and orbital couplings. Our method will enable us to study the anisotropy at microstructure interfaces. [1] Z. Torbatian, T. Ozaki, S. Tsuneyuki, and Y. Gohda, Appl. Phys. Lett. 104, 242403 (2014). [Preview Abstract] |
Monday, March 2, 2015 12:39PM - 12:51PM |
B30.00006: Tuning magnetic properties of metallic nanostructures on semi-insulating substrates Oleg Brovko, Valeri Stepanyuk In the past two decades, the properties of metallic nanostructures on metallic surfaces have been studied in minute detail and possibilities to tune them have been explored both experimentally and theoretically. [1] Recently the focus has been shifting towards insulating or semi-insulating substrates, [2] the reason being that while on metallic surfaces the magnetism of nanostructures is determined by the coupling of the localized magnetic moment of the ad-structure to a bath of itinerant electrons of the substrate, on insulating substrates the spin is largely isolated and often exhibits emergent quantum properties, fascinating from both fundamental and application points of view. Semi-insulating substrates open an additional possibility of adjusting the coupling of the ad-structure spin to the substrate. In the present contribution we show the possibility to tune magnetic properties of metal nanostructures and their interaction among each other on such semi-insulating substrates as thin decoupling CuN, h-BN and MgO layers. As a means of tuning we focus on adsorption site tailoring and exposure to external electric field. [1] O. Brovko et al., JPCM 26, 093001 (2014). [2] S. Loth et al., Science 335, 196 (2012), T. Schuh et al., Nano Lett. 12, 4805 (2012) [Preview Abstract] |
Monday, March 2, 2015 12:51PM - 1:03PM |
B30.00007: Effects of exchange interactions on magnetic anisotropy and spin-dynamics of adatoms on metallic surfaces Pedro Ruiz Diaz, Oleg Stepanyuk, Valeri Stepanyuk A common belief is that magneto-crystalline anisotropy energy (MA) mainly arises from the spin-orbit coupling interaction. Here, throughout an ab initio study we show that direct exchange interactions(Eex) together with substrate-mediated interactions rules the MA nature in Co inter- acting adatoms supported on Cu(001) and Pt(001) surfaces. MA exhibits a non-trivial behavior and is found to be strongly sensitive to Eex, magnetic order and substrate composition. Oscillatory magnetization switching is also revealed. Further, by means of a stochastic method, for the first time to our knowledge, the spin-dynamics of these single-spin systems assessed in the hysteresis loops is presented. Insights about the interplay between Eex and MA which determines the onset of the magnetization curves and their shape are inquired as well. [Preview Abstract] |
Monday, March 2, 2015 1:03PM - 1:15PM |
B30.00008: ABSTRACT WITHDRAWN |
Monday, March 2, 2015 1:15PM - 1:27PM |
B30.00009: A New Method Based on RF Impedance Technology and Soft Ferromagnetic Ribbons for Real-Time Corrosion Monitoring Izabella Berman, Jagannath Devkota, Hariharan Srikanth, Mahn-Huong Phan Development of a quick, cheap, and reliable technique to estimate the concentration of corrosive chemicals has been of technological interest for safety in industries and the environment for many years. Here we present a new approach for real-time monitoring of chemical corrosion based on the radio-frequency (RF) impedance technology and soft ferromagnetic ribbons. The impedance (Z), resistance (R), and reactance (X) of a commercial METGLAS\textregistered 2714A ribbon was measured in real time for 5 $\mu $l of drop-casted HNO3 of various concentrations. Variations in the concentration of the drop-casted acid were assessed by considering the difference ($\Delta )$ in the Z, R, and X with and without the acid treatment. The measurements performed at 0.2 MHz showed a large linear increase in the $\Delta $Z and $\Delta $R with the acid concentration which is ideal for developing highly sensitive chemical sensors. Since the ribbon used is commercially available at low cost and the measurement system is quick and low power consuming, the proposed sensor can be used as an easy, quick, and low-cost chemical probe in industries and environmental safety purposes. [Preview Abstract] |
Monday, March 2, 2015 1:27PM - 1:39PM |
B30.00010: Stochastic magnetization dynamics of biochemically bound magnetic nanoparticles Daniel Reeves, John Weaver Understanding the dynamics of magnetic nanoparticles in applied magnetic fields is critical for biosensing and therapeutic applications. In biological environments, the nanoparticles may clump together and the resultant dynamics are interesting and important. We show simulation schemes using stochastic Langevin equations that describe the particle rotations in various conditions and suggest ways to improve the applications. Biochemical binding is described in terms of changes of the size distribution from network theory perspective. Also, using log-normally size distributed particles, a master variable is derived that contains all the significant variables. This compacts the parameter space, quickens simulation, and improves intuition. An approximate closed form solution to the magnetization harmonics in an oscillating field is given in terms of this variable using the Langevin function. [Preview Abstract] |
Monday, March 2, 2015 1:39PM - 1:51PM |
B30.00011: Iron oxide nanoparticles with controlled morphology for advanced hyperthermia Zohreh Nemati Porshokouh, Hafsa Khurshid, Javier Alonso Messa, Manh-Huong Phan, Hariharan Srikanth Magnetic nanoparticles (NPs) are interesting for a wide range of applications. In biomedicine, they have been exploited for use in drug delivery, magnetic resonance imaging, and magnetic hyperthermia. While magnetic hyperthermia, using NPs to convert electromagnetic energy into heat to destroy the cancer cells, represents a novel cancer treatment technique, a poor heating conversion efficiency of the existing NPs restricts its practical use. Different strategies have been proposed to overcome this limitation, mainly by tuning the size, saturation magnetization and effective anisotropy of the NPs. Here we report a magnetic hyperthermia study on Fe3O4 NPs, where the effective anisotropy was tuned by varying particle morphology from the spherical to octopod shape. The Fe3O4 NPs were synthesized using a thermal decomposition method. Transmission electron microscopy (TEM) and high-resolution TEM images show high crystalline monodisperse nanoparticles. X-ray diffraction patterns confirm the presence of Fe3O4 phase. Hyperthermia experiments indicate that the octopods possess a higher SAR as compared to their spherical counterpart. Our findings provide an effective approach to improve the SAR of NPs by manipulating the shape anisotropy of the nanoparticles. [Preview Abstract] |
Monday, March 2, 2015 1:51PM - 2:03PM |
B30.00012: Magneto-impedance based detection of magnetically labeled cancer cells and bio-proteins J. Devkota, M. Howell, S. Mohapatra, T.H. Nhung, P. Mukherjee, H. Srikanth, M.H. Phan A magnetic biosensor with enhanced sensitivity and immobilized magnetic markers is essential for a reliable analysis of the presence of a biological entity in a fluid. Based on conventional approaches, however, it is quite challenging to create such a sensor. We report on a novel magnetic biosensor using the magneto-impedance (MI) effect of a Co-based amorphous ribbon with a microhole-patterned surface that fulfils these requirements. The sensor probe was fabricated by patterning four microholes, each of diameter 2 $\mu $m and depth 2 $\mu $m, on the ribbon surface using FIB lithography. The magnetically labeled Luis Lung Carcinoma (LLC) cancer cells and Bovine serum albumin (BSA) proteins were drop-casted on the ribbon surface, and MI was measured over 0.1 -- 10 MHz frequency range. As the analytes were trapped into the microholes, their physical motion was minimized and interaction among the magnetic fields was strengthened, thus yielding a more reliable and sensitive detection of the biological entities. The presence of magnetically labeled LLC cells (8.25x10$^{\mathrm{5}}$ cells/ml, 10 $\mu $l) and BSA proteins (2x10$^{\mathrm{11}}$ particles/ml, 10 $\mu $l) were found to result in a $\sim$ 2{\%} change in MI with respect to the reference signal. [Preview Abstract] |
Monday, March 2, 2015 2:03PM - 2:15PM |
B30.00013: Comparison of Coil Designs for Transcranial Magnetic Stimulation on Mice Priyam Rastogi, Ravi Hadimani, David Jiles Transcranial magnetic stimulation (TMS) is a non-invasive treatment for neurological disorders using time varying magnetic field. The electric field generated by the time varying magnetic field is used to depolarize the brain neurons which can lead to measurable effects. TMS provides a surgical free method for the treatment of neurological brain disorders like depression, post-traumatic stress disorder, traumatic brain injury and Parkinson's disease. Before using TMS on human subjects, it is appropriate that its effects are verified on animals such as mice. The magnetic field intensity and stimulated region of the brain can be controlled by the shape, position and current in the coils. There are few reports on the designs of the coils for mice. In this paper, different types of coils are developed and compared using an anatomically realistic mouse model derived from MRI images. Parameters such as focality, depth of the stimulation, electric field strength on the scalp and in the deep brain regions, are taken into account. These parameters will help researchers to determine the most suitable coil design according to their need. This should result in improvements in treatment of specific disorders. [Preview Abstract] |
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