Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Z30: Focus Session: Frontiers in Magnetism II |
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Barbara Jones, IBM Almaden Research Center Room: 206B |
Friday, March 6, 2015 11:15AM - 11:27AM |
Z30.00001: Electronic properties of transition metal atoms on Cu2 N/Cu(100): a DFT comparative study Alejandro Ferron, Jos\'e Lado, Joaqu\'In Fern\'andez-Rossier We study the electronic and magnetic properties of individual transition metal atoms (Ti, V, Cr, Mn, Fe, Co and Ni) deposited on a Cu$_2$N$/$Cu($100$) surface by means of spin-polarized density functional theory (DFT) calculations. We focus our work on a comparative study of the various quantities, such as magnetic moment, orbital occupation, structural properties, hybridization with the substrate and spin polarization of the substrate, paying attention to the trends as the transition metal is changed. In this work we try to go beyond existing theoretical works by providing a comprehensive and comparative study of the electronic, magnetic and structural properties of these seven atoms including also Ni, for which there are no published calculations to the best of our knowledge. In the case of Mn, Fe and Co, we connect our results with the existing scanning tunneling microscope experiments [1,2].\\[4pt] [1] J. Oberg, R. Calvo, F. Delgado, D. Jacob, M. Moro, D. Serrate, J. Fern\'andez-Rossier, C. Hirjibehedin, Nature Nanotechnology, {\bf 9}, 64 (2014).\\[0pt] [2] A. Spinelli, B. Bryant, F. Delgado, J. Fern\'andez-Rossier, A. F. Otte, Nature Materials, published online on July 6 (2014). doi:10.1038/nmat4018 [Preview Abstract] |
Friday, March 6, 2015 11:27AM - 11:39AM |
Z30.00002: Ni adsorption on $\textrm{MgO}(001)$: A Comparison of DFT and DFT$ + $U Oliver Albertini, Amy Liu, Barbara Jones The study of magnetic atoms on surfaces has drawn recent attention due to possible applications in the realm of magnetic storage and quantum computing. Researchers are looking across the 3d transition metal series for candidates with high magnetic anisotropy. Here we examine the MgO/Ag surface with a Ni adatom using DFT and DFT+U computational approaches. We investigate the preferential binding site and the interesting physics involved in the resulting magnetic moment, drawing comparisons with a recent study of Co on MgO/Ag. [Preview Abstract] |
Friday, March 6, 2015 11:39AM - 11:51AM |
Z30.00003: Magnetocrystalline anisotropy ``space'' distribution over atoms from different first principles approaches Roman Chepulskyy, Dmytro Apalkov Interplays between bulk vs interface and electron hybridization vs stress contributing into the magnetocrystalline anisotropy are studied from first pronciples. Fe/MgO system is considered as example with variable Fe thickness. The effect of stress is modeled by consideration of a number of fixed in-plane lattice parameters with full relaxation in z-direction. Different approaches to calculate separate atom contributions into the total magnetocrystalline anisotropy are compared and controversies are discussed [Preview Abstract] |
Friday, March 6, 2015 11:51AM - 12:03PM |
Z30.00004: Electric field control of Martensitic Phase Transitions in Thin Films of Ni-Mn-In Nabil Al-Aqtash, Andrei Sokolov, Renat Sabirianov We propose the electric field control of martensite transformation of Ni-Mn-In thin films deposited on ferroelectric (FE) substrate. DFT- based calculations indicate that the off-stochiometric Ni2Mn1.5In0.5 alloy shows that the ferromagnetic (FM) cubic phase undergoes transformation to tetragonal ferromagnetic (FiM) martensite phase at low temperature. The presence of FE substrate changes the relative stability of FM austenite and FiM martensite phases. (SrZrO3/PbZrO3) superlattices were considered as FE substrates with polarization perpendicular to the interface. The relative stability of two phases of the thin films can be tuned by polarization reversal in FE due to the change in sign of induced charges at the interface. The energetically favorable structures of the FE/Ni2Mn1.5In0.5 systems depend on interface structure between FE and Ni2Mn1.5In0.5 layers, e.g Ni-(Pb-O) interface. The energy difference (per NiMnIn f.u) between FM austenite and FiM martensite states of the film on FE substrate is $\Delta $E $=$ 0.22 eV with polarization away from interface, upon polarization reversal $\Delta $E $=$ 0.75 eV, compared to ($\Delta $E $=$ 0.24 eV) in the bulk. Additionally Pb atoms in PbO3 planes shifted in opposite direction with respect to oxygen planes and alter the chemical bonding of Pb with Ni atoms of the thin films. These changes possibly cause the shift of the martensite transition temperature. These results clearly indicate the possibility of control of martensitic transition in Ni-Mn-In thin films by FE substrate. [Preview Abstract] |
Friday, March 6, 2015 12:03PM - 12:15PM |
Z30.00005: Ab initio calculation of magnetic interactions and time-dependent density functional theory simulation for ultrafast magnetic dynamics Zhanghui Chen, Lin-Wang Wang The competition between exchange interaction and spin-orbital coupling, especially in the presence of the symmetry-breaking of interfaces, provides a path to magnetic interactions which can cause novel magnetic structures like skyrmions. We will use a noncollinear spin ab initio calculation to predict the spin-spin interactions near such interfaces. A new algorithm is developed for such calculations. Similarly, a newly developed fast time-dependent density functional theory algorithm will be used to study femtosecond spin relaxation after an initial excitation by a fast laser pulse. Such simulation is mean to reveal the underlying mechanism which causes fast magnetic decays. [Preview Abstract] |
Friday, March 6, 2015 12:15PM - 12:27PM |
Z30.00006: Impact of self-assembled monolayers on spin injection characteristics in Co/organic systems Curt A. Richter, Hyuk-Jae Jang, Sujitra J. Pookpanratana, Christina A. Hacker, Jun-Sik Lee, Ich C. Tran One of the key factors to realize spin injection and transport through organic semiconductors is the understanding and engineering of the spin-dependent phenomena at the interface between a ferromagnetic metal and an organic semiconductor. We present the results of experiments that explore the influence of self-assembled monolayers (SAMs) on spin injection into Alq3, an organic semiconductor, from a ferromagnetic metal, Co. Two different SAMs, MHA (16-mercaptohexadecanoic acid) and ODT (1-octadecanethiol) are inserted between Alq3 and Co layers and their effects on hybridization and related changes in energetics and spin dependent properties at the interface are investigated. Co is an easily oxidized surface. We find that the self-assembly of the bifunctional molecule, MHA, is profoundly different than ODT on oxidized Co. We propose an interface formation model and discuss the impact of this Co/molecule interface on electron transport. Ultraviolet photoelectron spectroscopy data reveal that when directly attached to unoxidized Co, both MHA and ODT treatments lower the Co work function. X-ray magnetic circular dichroism spectra imply that SAMs reduce the hybridization between Co and Alq3 and furthermore, they enhance the spin magnetic moment of Co. [Preview Abstract] |
Friday, March 6, 2015 12:27PM - 12:39PM |
Z30.00007: ABSTRACT WITHDRAWN |
Friday, March 6, 2015 12:39PM - 12:51PM |
Z30.00008: Magnetization studies and spin Hamiltonian modelling of Li2(Li1-xFex)N James H. Atkinson, Anton Jesche, Enrique del Barco, Paul C. Canfield The study of ferromagnetic materials has yielded many examples of compounds which exhibit large energy barriers to a reversal of magnetization and correspondingly wide magnetization versus field hysteresis loops. Some materials, such as members of the class called ``single-molecule magnets'' (SMMs), even display vivid signatures of quantum tunneling effects, manifested as step-like features in hysteresis loop measurements of crystalline ensembles. The compound Li2(Li1-xFex)N has been previously shown to display an extremely high blocking temperature ($\sim$ 20 K) and large coercive fields (\textgreater 11 T), as well as step-like features like those seen in SMMs [1]. Here we report the results of low-temperature Hall sensor magnetization studies on a crystalline sample of Li2(Li1-0.006Fe0.006)N in which we detail evidence of a preferential orientation for the observed features, as well as their dependence upon transverse component fields in their magnitude, behavior which we attempt to model with a giant spin Hamiltonian. [1] A. Jesche, R.W. McCallum, S. Thimmaiah, J.L. Jacobs, V. Taufour, A. Kreyssig, R.S. Houk, S.L. Bud'ko {\&} P.C. Canfield. Nature Comm., 5, 3333 (2014). [Preview Abstract] |
Friday, March 6, 2015 12:51PM - 1:03PM |
Z30.00009: Searching for Emergent Ferromagnetism in 2D systems with Random Easy Axis Anisotropy Donald Priour Using large scale Monte Carlo calculations, we determine if random anisotropy in the interactions among neighboring magnetic moments may stabilize long-range ferromagnetic order at finite temperatures in the case of $XY$ and Heisenberg models on a two dimensional lattice where low energy excitations (e.g. spin waves) would eliminate bulk ferromagnetism for $T > 0$. We include a magnetic anisotropy in the coupling among magnetic moments causing neighboring spins to preferentially align along a randomly directed axis with the extent of the preference specified by an anisotropy parameter $\gamma$. We determine the magnetic phase diagram with respect to $\gamma$, and we explore the possibility that intermediate anisotropy levels could support finite temperature ferromagnetism, which would be overwhelmed by thermally excited spin waves in the weak anisotropy regime ($\gamma \ll 1$) and revert to a non-ferromagnetic phase for strong anisotropy ($\gamma \gg 1$) where the disordering influence of the randomly directed easy axes prevents magnetic moments from orienting in the same direction. In addition to finite size scaling analyses to extract critical exponents for any finite temperature ferromagnetic phase, we calculate the energy spectrum and density of states for spin waves. [Preview Abstract] |
Friday, March 6, 2015 1:03PM - 1:15PM |
Z30.00010: Nanostructured Mn2Ga Alloys with High Magnetization and Coercivity Ahmed A. ElGendy, George Hadjipanayis Mn-based alloys have attracted much interest lately for the development of rare earth free magnets because of their high magnetocrystalline anisotropy. [1]. In this study, we have prepared nanostructured Mn2Ga alloys with the pure D022 phase by subjecting ball milled powders with micron size grains to the supercritical conditions of fluids at high pressure of 850 psi and temperature of 250 oC. The use of supercritical fluids was found to lead to a homogeneous microstructure with an average grain size of 35 nm. The magnetic properties show an enhancement of magnetization and coercivity from M(3T)$=$ 30 emu/g and HC $=$3 kOe in the micron size powders to M(3T) and HC of 48 emu/g and 4.7 kOe, respectively in the nanosize powders. This new method of grain size reduction to nanoscale with the subsequent increase in coercivity via the high pressure cell opens new routes for rare earth-free permanent magnet development. The work was funded by NSF-G8. References: Cui, B. Z.; Marinescu, M.; Liu, J. F. Ferromagnetic Tetragonal L10-type MnGa Isotropic Nanocrystalline Microparticles. IEEE Trans. Mag. 2013, 49(7), 3322-3325. [Preview Abstract] |
Friday, March 6, 2015 1:15PM - 1:27PM |
Z30.00011: Application of Barkhausen noise and ferromagnetic hysteresis for magnetic non-destructive evaluation of multiphase composites and structures Neelam Prabhu Gaunkar, Orfeas Kypris, Cajetan Nlebedim, David Jiles Composite ferromagnetic materials with multiple magnetic phases are increasingly being used in applications such as magnetic data storage, magnetic sensors and actuators and exchange-spring magnets. These materials occur in single or multiphase conditions and can undergo phase changes over time or during processing. For these materials, we examine the interrelation between ferromagnetic hysteresis, Barkhausen noise and the material microstructure. We observe that the presence of a second phase in these materials can be detected with the help of Barkhausen noise signals due to the occurrence of additional peaks in the magnetization envelope. This behavior in the magnetic response can serve as a tool for non-destructive evaluation of ferromagnetic materials for which phase constitution and phase changes affect the structural performance.~ [Preview Abstract] |
Friday, March 6, 2015 1:27PM - 1:39PM |
Z30.00012: Development of Gallium-Indium Alloys, Nonmagnetic Test Masses for Exotic Spin-Dependent Force Searches Marjan Khosravi, Rakshya Khatiwada, William M. Snow Possible new spin-dependent short-range forces of nature in the mm to $\mu $m range which couple to nucleons are now sought in many experiments. Most experiments search for this possible interaction through NMR frequency shifts of polarized nuclei with the introduction of an unpolarized test mass nearby [1]. However, any nonzero magnetic susceptibility of this test mass can produce a systematic error in the measurement. We therefore seek materials with magnetic susceptibilities as close as possible to zero. We synthesized Gallium-Indium (Ga-In) alloys with various Indium percentages which are liquid at room temperature and measured their magnetic susceptibilities using a torsion balance-based commercial device. The measured magnetic susceptibilities range from $-$0.06E-06 to $-$0.12E-06 cgs volume susceptibility and are consistent with the weighted average of the component susceptibilities. The values are about an order of magnitude lower than water for a substance possessing 4.7 times larger nucleon density. [1] P. H. Chu, A. Dennis, C. B. Fu, H. Gao, R. Khatiwada, G. Laskaris, K. Li, E. Smith, W. M. Snow, H. Yan, and W. Zheng, Phys. Rev. D 87, 011105(R) (2013) [Preview Abstract] |
Friday, March 6, 2015 1:39PM - 1:51PM |
Z30.00013: First-principles study of magnetic interactions in 3d transition metal-doped phase-change materials Tetsuya Fukushima, Hiroshi Katayama-Yoshida, Kazunori Sato, Hitoshi Fujii, Elias Rabel, Rudolf Zeller, Peter Dederichs, Wei Zhang, Riccardo Mazzarello We investigate the electronic structure and the magnetic properties of the prototypical phase-change material Ge$_{2}$Sb$_2$Te$_5$ (GST) doped with V, Cr, Mn and Fe by density functional calculations. Both the supercell method and the coherent potential approximation (CPA) are employed to describe this complex substitutionally disordered system. As regards the first approach, we consider a large unit cell containing 1000 sites to model the random distribution of the cations and of the impurities in doped cubic GST. Such a large-scale electronic structure calculation is performed using the program KKRnano, where the full potential screened Korringa-Kohn-Rostoker Green's function method is optimized by a massively parallel linear scaling all electron algorithm. We find that ferromagnetic states are favorable in the cases of V and Cr doping, due to the double exchange mechanism. The ferromagnetic interaction is particularly strong in the case of Cr. As a result, high Curie temperatures close to room temperatures are obtained for large Cr concentration. [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