Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Y7: Focus Session: Magnetic Structures: Novel Mechanisms and Experimental Exploration |
Hide Abstracts |
Sponsoring Units: GMAG Chair: Aakash Pushp, IBM Research Room: 106 |
Friday, March 7, 2014 8:00AM - 8:12AM |
Y7.00001: Towards magnetic 3D x-ray imaging Peter Fischer, R. Streubel, M.-Y. Im, D. Parkinson, J.-I. Hong, O.G. Schmidt, D. Makarov Mesoscale phenomena in magnetism will add essential parameters to improve speed, size and energy efficiency of spin driven devices. Multidimensional visualization techniques will be crucial to achieve mesoscience goals. Magnetic tomography is of large interest to understand e.g. interfaces in magnetic multilayers, the inner structure of magnetic nanocrystals, nanowires or the functionality of artificial 3D magnetic nanostructures. We have developed tomographic capabilities with magnetic full-field soft X-ray microscopy combining X-MCD as element specific magnetic contrast mechanism, high spatial and temporal resolution due to the Fresnel zone plate optics [1]. At beamline 6.1.2 at the ALS (Berkeley CA) a new rotation stage allows recording an angular series (up to 360 deg) of high precision 2D projection images. Applying state-of-the-art reconstruction algorithms it is possible to retrieve the full 3D structure. We will present results on prototypic rolled-up Ni [2] and Co/Pt tubes and glass capillaries coated with magnetic films and compare to other 3D imaging approaches e.g. in electron microscopy [3]. \\[4pt] [1] P. Fischer, Mat. Sci {\&} Eng. R72 81 (2011)\\[0pt] [2] R. Streubel et al., doi:10.1002/adma.201303003.\\[0pt] [3] C. Phatak et al, Ultramicroscopy 109 264 (2009) [Preview Abstract] |
Friday, March 7, 2014 8:12AM - 8:24AM |
Y7.00002: Magnetic contrast tuning with nonlinear magneto-plasmonics Wei Zheng, Aubrey T. Hanbicki, Berend T. Jonker, Gunter Lupke Magneto-plasmonics describes systems where plasmonic and ferromagnetic properties coexist. The nonlinear-optical magnetic second-harmonic generation (MSHG) technique is extremely sensitive to subtle modifications of the spin-polarized electronic structure of transition metal surfaces, the same region where surface plasmons (SP) are present. This technique, which builds a direct link between plasmonics and the magneto-optical effect, is called nonlinear magneto-plasmonics. We will present results of experiments that show that not only can the MSHG signal be enhanced by SPs in an attenuated total reflection (ATR) condition, but also that the magnetic contrast can be tuned by the angle-of-incidence. Furthermore, the magnetic contrasts of transverse and longitudinal MSHG display opposite trends. The tuning effect originates from the change of relative phase between magnetic and non-magnetic MSHG components. This new effect enhances the sensing of magnetic switching which has potential usage in quaternary magnetic storage systems and bio-chemical sensors due to its very high surface sensitivity. [Preview Abstract] |
Friday, March 7, 2014 8:24AM - 8:36AM |
Y7.00003: Faraday Rotation Spectrum of Bismuth-Doped Rare-Earth Iron Garnets for Magneto-Optic Sensor Applications Mannix Shinn, Dong Ho Wu, Anthony Garzarella, Rongjia Tao Iron garnet Faraday rotators are a promising sensor material for measuring magnetic fields. The rotator's field sensitivity increases inversely with wavelength and beam path, but so does the insertion loss. We wish to optimize sensor sensitivity by studying the transmission coefficient and Verdet constant over a spectrum from 0.4 to 2 um in samples of bismuth-doped rare-earth iron garnet. Data for two different gallium doped samples will be presented, including data of other magnetic field dependent effects that were observed. [Preview Abstract] |
Friday, March 7, 2014 8:36AM - 8:48AM |
Y7.00004: Material dependence of magnetic hysteresis in single nanometer-scale ferromagnetic particles Patrick Gartland, Wenchao Jiang, Dragomir Davidovic The characteristics of ferromagnetic particles change remarkably when their size approaches the nanometer scale and below. We conduct single-electron tunneling experiments to study the breakdown of magnetic hysteresis in single particles 2-5 nm in diameter, made of Co, Fe, Ni, and Py=Ni$_{0.8}$Fe$_{0.2}$. At $T=4.2$K and at mK-temperature, we observe a dramatic difference in magnetic hysteresis among these metals: All of the Co and Fe particles, but only 4\% of the Ni particles exhibit magnetic hysteresis. The tunneling spectra of Ni particles at mK-Temperature display evidence of ferromagnetism, despite the absence of hysteresis. We will present recent experimental data that will shed light on the possible mechanisms driving this strong suppression of hysteresis in Ni. [Preview Abstract] |
Friday, March 7, 2014 8:48AM - 9:00AM |
Y7.00005: Assembly of Magnetic Nanoclusters Balamurugan Balasubramanian, Ralph Skomski, Bhaskar Das, George Hadjipanayis, David Sellmyer Nanostructured Co or Fe-rich magnetic materials are of interest for a wide range of applications because of their novel structures and spin phenomena [1, 2]. In this presentation, the synthesis and stability of nanoparticles of (Co-Fe):X alloys (X $=$ Hf, Sm, Si) having unusual crystal structures will be discussed. The nanoparticles are produced using a single step-process in a cluster-deposition system and are smaller than 10 nm with an rms standard deviation of $\sigma $/$d \le $ 0.15. In particular, Co-rich nanoparticles such as HfCo$_{\mathrm{7}}$ and SmCo$_{5}$ exhibit high magnetocrystalline anisotropies ($K_{1}$ \textgreater 10 Mergs/cm$^{3})$ and saturation magnetic polarizations ($J_{s}$ \textgreater 10 kG). The nanoscale effects on the magnetism including spin structure, magnetic polarization, and other intrinsic properties, and the potential of the nanostructures for various applications will be presented. \\[4pt] [1] B. Balamurugan, B. Das, V.R. Shah, R. Skomski, X.Z. Li, and D.J. Sellmyer, \textit{Appl. Phys. Lett.} 101, 122407 (2012).\\[0pt] [2] Advanced Magnetic Nanostructures, Eds. D.J. Sellmyer and R. Skomski. Springer: New York, 2001. [Preview Abstract] |
Friday, March 7, 2014 9:00AM - 9:12AM |
Y7.00006: Structure and magnetism of nanostructured Zr$_{2}$Co$_{11}$ Bhaskar Das, Balamurugan Balasubramanian, Wenyong Zhang, Ralph Skomski, David Sellmyer Recently nanostructured Zr$_{2}$Co$_{11}$-based alloys crystallizing in the rhombohederal structure have emerged as novel magnetic material with an appreciable magnetocrystalline anisotropy constant ($K_{1}\approx $ 20 Mergs/cm$^{3}$), a high saturation magnetic polarization ($J_{s} \ge $ 10 kG), and a high Curie temperature ($T_{c} \approx $ 783 K) [1, 2]. The nanostructured Zr$_{2}$Co$_{11}$ films were fabricated using cluster-deposited nanoparticles of smaller than 10 nm as building blocks. The nanoscale effect on structure and room-temperature magnetic properties was investigated by comparing those of melt-spun bulk alloys. In addition, the magnetic properties at elevated temperatures also will be discussed and this will provide a further insight to understand the magnetism of Zr$_{2}$Co$_{11}$ nanostructures and explore the possibility of using them for high-temperature applications.\\[4pt] [1] B. Balamurugan, B. Das, R. Skomski, W. Y. Zhang and D. J. Sellmyer, \textit{Adv. Mater. }25, 6089 (2013) \\[0pt] [2] B. Balamurugan, B. Das, R. Skomski, W. Y. Zhang and D. J. Sellmyer, \textit{J. Phys.: Condens. Matter.} (in press). [Preview Abstract] |
Friday, March 7, 2014 9:12AM - 9:24AM |
Y7.00007: Insight into the Slater-Pauling behavior of Permalloy-Cu alloys Ronny Knut, Justin Shaw, Hans Nembach, Patrik Grychtol, Emrah Turgut, Dmitriy Zusin, Henry Kapteyn, Margaret Murnane, Dario Arena, Erna Delczeg, Olle Eriksson, Olof Karis, Tom Silva Magnetic 3d transition alloys are of great importance, but a rigorous understanding of the magnetization for these systems remains elusive. While it is well-known that the average magnetic moment of 3d transition metal alloys obey Slater-Pauling, the oft-cited basis for our understanding of this ``law'' is suspect: The high-valence side of Slater-Pauling was originally explained by Slater via rigid-band theory (RBT), with the primary effect to be the filling of the minority d-band with valence electrons upon alloying. However, many ab-initio calculations do not support RBT since alloying affects the band-structure. We used X-ray magnetic circular dichroism to test the veracity of RBT as a model for Slater-Pauling behavior for Permalloy-Cu alloys, (Ni0.8Fe0.2)xCu1-x. We find that our data agrees with Slater-Pauling regarding average magnetic moments. Also, the dilution of Permalloy by Cu does result in some charge transfer from Cu to Ni/Fe, in qualitative agreement with RBT, but the charge transfer is inadequate to explain the dependence of spin moment on Cu concentration. Of equal importance is the decrease of exchange splitting due to the reduced number of magnetic neighbors. [Preview Abstract] |
Friday, March 7, 2014 9:24AM - 9:36AM |
Y7.00008: Experimental Monocrystalline Micromagnetics: A Vortex Spin Topology with Cubic Anisotropy in YIG Lance C. Parsons, Joseph E. Losby, Fatemeh Fani Sani, Dylan T. Grandmont, Zhu Diao, Tayyaba Firdous, Douglas Vick, Wayne K. Hiebert, Mark R. Freeman The detailed magnetostatic characterization of an individual, single-crystalline yttrium iron garnet micromagnetic disk is reported. The crystalline orientation is such that a (111) direction of the cubic crystal structure is perpendicular to the disk surface. An easy axis is thus aligned with the core of the magnetic vortex state. The 600 nm-thick, 600 nm-radius disk is transferred to a nanomechanical torsional resonator for characterization by torque magnetometry. The experimental results show a pristine, Barkhausen-free low field response of the vortex magnetization to in-plane field. For angular measurements of magnetic hysteresis as a function of the in-plane direction of applied magnetic field, it is observed that the field strengths at which the vortex annihilation transition occurs are significantly less sensitive to magnetic anisotropy than are the nucleation fields. Micromagnetic simulation results show a rich, topologically stable structure owing to the disk thickness and monocrystalline nature. The comprehensive magnetostatic measurements yield an incisive determination of the degree to which ideal micromagnetic response has been approached in the fabricated disk, and of the role of magnetocrystalline anisotropy on vortex behavior and topological spin structure. [Preview Abstract] |
Friday, March 7, 2014 9:36AM - 9:48AM |
Y7.00009: Determination of the electronic state of Er in sputtered AlN:Er films by magnetic measurements V. Narang, M.S. Seehra, D. Korakakis The optoelectronic [1] and piezoelectric [2] properties of AlN:Er thin films for device applications have been of great recent interest. The magnitude of optical activity depends on local crystalline environments of Er [3]. Here we focus on the electronic state of Er in AlN:Er (1.6 at.\%) films prepared by reactive magnetron sputtering on Si substrate. X-ray diffraction of the films shows that Er doping expands the lattice and XPS studies confirm the presence of Er. To determine if Er is present as Er metal, Er$_{2}$O$_{3}$ or Er$^{3+}$ substituting for Al$^{3+}$, magnetization was measured vs. temperature (2 K to 300 K) in H = 1kOe and data is found to fit the Curie law with a magnetic moment ${\mu}$ = 4.85 ${\mu}$$_{B}$ per Er, in good agreement with expected value for Er$^{3+}$ substituting for Al$^{3+}$ in AlN [4]. The presence of Er$_{2}$O$_{3}$ and Er metal is ruled out since magnetic transitions expected for Er$_{2}$O$_{3}$ (Er metal) at 3.4 K ({$\sim$}30 K) are not observed, thus establishing that Er substitutes for Al as Er$^{3+}$ in the AlN:Er films.\\[4pt] [1] A.R. Zanatta et al, J. Appl. Phys., 98, 093514 (2005);\\[0pt] [2] V. Narang et al, MRS Symp. Proc. 1519 (2013);\\[0pt] [3] R.G. Wilson et al, Appl. Phys. Lett., 66, 992 (1994);\\[0pt] [4] S. Yang, et al, J. Appl. Phys., 105, 023714 (2009) [Preview Abstract] |
Friday, March 7, 2014 9:48AM - 10:00AM |
Y7.00010: Control of magnetization alignment in magnetic nanocontacts Gavin D. Scott Transport measurements together with finite element micromagnetic simulations are used to investigate the magnetoresistance response of permalloy break junction devices. Ferromagnetic nanogap and point contact structures may be used to study the interplay between Kondo correlations and magnetic excitations by tuning the source and drain contact magnetization configuration. However, the magnetization of the leads is not trivially related to the precise arrangement of domain walls at the nanocontact tip region most relevant to transport. The shape anisotropy of elliptical electrodes together with improved fabrication techniques lead to competition between exchange and magnetostatic energies that may result in desirable source-drain magnetization alignments free of vortex states. [Preview Abstract] |
Friday, March 7, 2014 10:00AM - 10:12AM |
Y7.00011: Magnetic structures of the anisotropic Dirac metals AMnBi$_{2}$ (A $=$ Ca, Sr) Yanfeng Guo, Andrew Princep, Pascal Manuel, Dimitry Khalyavin, Andrew Boothroyd Magnetism is potentially important in the Dirac materials AMnBi$_{2}$ (A $=$ Sr and Ca) because long-range magnetic order of the Mn spins provides an additional periodic potential that could influence the Fermi surface and hence the behavior of the Dirac fermions. We report powder and single crystal neutron diffacraction measurements of the magnetic order in AMnBi$_{2}$ (A $=$ Sr and Ca), two layered manganese pnictides with anisotropic Dirac fermions on a Bi square net. Both compounds are found to order in k $=$ 0 antiferromagnetic structures, with ordered Mn moments at T $=$ 10 K of approximately 3.8 $\mu_{\mathrm{B}}$ aligned along the c axis. The magnetic structures are N\'{e}el-type within the Mn-Bi layers, consistent with density functional theory predictions, but the interlayer ordering is different in the two materials, being antiferromagnetic in SrMnBi$_{2}$ and ferromagnetic in CaMnBi$_{2}$. This allows a mean-field coupling of the magnetic order to the Dirac fermions in CaMnBi$_{2}$, but not in SrMnBi$_{2}$. [Preview Abstract] |
Friday, March 7, 2014 10:12AM - 10:24AM |
Y7.00012: Orbital order and Hund's rule frustration in Kondo lattices Kazushi Aoyama, Leonid Isaev, Indranil Paul, Ilya Vekhter We analyze a microscopic origin of the Kondo effect-assisted orbital order in heavy-fermion materials. By studying the periodic two-orbital Anderson model with two local electrons, we show that frustration of Hund's rule coupling due to the Kondo effect leads to an incommensurate spiral orbital and magnetic order, which exists only inside the Kondo screened (heavy-electron) phase. This spiral state can be observed in neutron and resonant X-ray scattering measurements in ${\rm U}$- and ${\rm Pr}$-based heavy-fermion compounds, and realized in cold atomic gases, e.g. fermionic ${}^{173}{\rm Yb}$. [Preview Abstract] |
Friday, March 7, 2014 10:24AM - 10:36AM |
Y7.00013: Toroidal ordering in metals: band shift, magnetotransport, and magnetoelectric effect Satoru Hayami, Hiroaki Kusunose, Yukitoshi Motome The electromagnetic effect, interplay between electronic and magnetic properties, is one of the most interesting issues in condensed matter physics. Recently, it has been studied intensively in magnetic insulators without spatial-inversion and time-reversal symmetries. Especially, a toroidal moment defined by a vector product of magnetization and electronic polarization has attracted interest because it leads to intriguing phenomena, such as a linear electromagnetic effect and nonreciprocal directional dichroism. It, however, has not been fully understood how such toroidal ordering affects the electronic structure and transport property in metallic systems. In order to clarify this issue, we investigate a microscopic model for locally noncentrosymmetric systems. Starting from an $s$-$p$ four-band tight-binding model with local inversion symmetry breaking, we derive an effective model with the antisymmetric spin-orbit coupling. By analyzing the model at the mean-field level, we find that a ferroic ordering of a microscopic toroidal moment acts as an effective gauge field, which leads to a center-of-mass momentum shift in the band structure. Furthermore, within the linear response theory, we show that toroidal ordering induces anomalous magnetotransport and magnetoelectric effects. [Preview Abstract] |
Friday, March 7, 2014 10:36AM - 10:48AM |
Y7.00014: Stability of the helical spin mode in RKKY systems with disorder Younghyun Kim, Meng Cheng, Bela Bauer, Roman Lutchyn Motivated by the experimental proposals[1-4] trying to realize topological superconductivity and Majorana zero-energy modes in RKKY systems, we study magnetic properties of one-dimensional spin chains consisting of localized magnetic moments coupled by itinerant electrons via the Rudermann-Kittel-Kasuya-Yosida (RKKY)-type interaction. As a source of itinerant electrons, we consider one- and two-dimensional electron gas with spin-orbit coupling. We obtain the phase diagram of the system in the presence of Rashba spin-orbit coupling in a clean limit, and identify the stability regions for the helical spin mode. We then examine the stability of this mode using diagrammatic techniques and Monte Carlo in presence of disorder. [1] S. Nadj-Perge, I. K. Drozdov, B. A. Bernevig, and Ali Yazdani, Phys. Rev. B 88, 020407(R) (2013) [2] Jelena Klinovaja, Peter Stano, Ali Yazdani, and Daniel Loss, Phys. Rev. Lett. 111, 186805 (2013) [3] M. M. Vazifeh and M. Franz, Phys. Rev. Lett. 111, 206802 (2013) [4] Bernd Braunecker and Pascal Simon, Phys. Rev. Lett. 111, 147202 (2013) [Preview Abstract] |
Friday, March 7, 2014 10:48AM - 11:00AM |
Y7.00015: Helimagnetism in Cr doped FeGe Yuen Yiu, Nirmal Ghimire, Lisa Debeer-Schmitt, Michael McGuire, Arnab Banerjee, Ken Littrell, David Mandrus, Stephen Nagler We have studied helimagnetism in Fe(1-x)Cr(x)Ge via bulk magnetic measurements and Small Angle Neutron Scattering (SANS). Cubic FeGe exhibits helimagnetism below Tc = 276 K. This transition is suppressed by Cr doping, and cannot be detected above 4K for x = 0.4 or greater. SANS measurements for samples with x = 0.1, 0.2, and 0.3 shows clear evidence for helimagnetic structures with characteristic periods of several hundred angstroms. The x = 0.2 and 0.3 samples show a hump in the susceptibility accompanied by an anomaly in the SANS signal at a temperature below the onset of helimagnetic order. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700