1 Study of the anomalous magnetic behavior of nanostructures by X-ray magnetic circular dichroism Rogerio Magalhães-Paniago #,*, #Departamento de Física, UFMG, Belo Horizonte, Brazil * Laboratório Nacional de Luz Síncrotron, Campinas SP, Brazil
2 Overview 1. Tutorial: what is X-ray Magnetic Circular Dichroism 2. Scientific cases: A. Anomalous Palladium magnetism in nanostructures B. Giant orbital magnetic moment of Co/Au nanostructures C. Magnetic domain reconfiguration in MnAs/GaAs films D. Fe/MnAs magnetic coupling E. Microscopy with magnetic domain sensitivity 4. Conclusion
3 1. Tutorial: what is X-ray Magnetic Circular Dichroism (XMCD) XMCD reflects the dependence of photon absorption of a material on polarization. X-ray absorption spectroscopy utilizes the energy dependent absorption of x-rays to obtain information about the elemental composition X-ray absorption spectra of a wedge sample, revealing the chemical composition
4 1. Tutorial: what is X-ray Magnetic Circular Dichroism (XMCD) It also gives information on the chemical environment of the atoms and their magnetic state. Core electrons are excited in the absorption process into empty states above the Fermi energy and thereby probe the electronic and magnetic properties of the empty valence levels. L-edge x-ray absorption edge spectra of Fe, Co and Ni in the form of the elemental metals and as oxides. They two main structures are called the L3 (lower energy) and L2 absorption edges. The two main peaks in the spectra arise from the spin orbit intera ction of the 2p core shell and the total intensity of the peaks is proportional to the number of empty 3d valence states.
5 1. Tutorial: what is X-ray Magnetic Circular Dichroism (XMCD) The metals are usually ferromagnetic and their magnetic properties are best studied with X-Ray Magnetic Circular Dichroism spectroscopy, while the oxides are usually antiferromagnetic and are studied with X-Ray Magnetic Linear Dichroism.
6 1. Tutorial: The concept of XMCD Spin and Orbital Moments X-ray absorption process spin dependent Use of right or left circularly polarized photons transfer angular momentum to the excited photoelectron p 3/2 (L3) and p 1/2 (L2) levels have opposite spin-orbit coupling spin polarization opposite at the two edges Electronic transitions in conventional L-edge x-ray absorption (a), and x-ray magnetic circular x-ray dichroism (b,c), illustrated in a one-electron model. The transitions occur from the spin-orbit split 2p core shell to empty conduction band states. By use of circularly polarized x-rays the spin moment (b) and orbital moment (c) can be determined from linear combinations of the dichroic difference intensities A and B, according to other sum rules.
7 1. Tutorial: The concept of XMCD Spin and Orbital Moments
8 1. Tutorial: The concept of XMCD Spin and Orbital Moments m(e) - X-ray absorption for different polarizations Dm(E) = XMCD signal Usually one inverts the magnetic field instead of changing polarizations
9 1. Tutorial: XMCD Spin and Orbital Moments sum rules m(e) - X-ray absorption for different polarizations Dm(E) = m + (E) - m - (E) (XMCD signal) L 3 L 2
10 1. Tutorial: XMCD Spin and Orbital Moments sum rules
11 1. Tutorial: XMCD Spin and Orbital Moments sum rules C. T. Chen et al., Phys. Rev. Lett. 75, 152 (1995) Theoretical papers: B. T. Thole et al., Phys. Rev. Lett. 68, 1943 (1992) P. Carra et al., Phys. Rev. Lett. 70, 694 (1993)
12 1. Tutorial: XMCD Spin and Orbital Moments sum rules
13 2. Scientific cases: A. Anomalous Palladium magnetism in nanostructures Techniques: DRX,TEM, SQUID Ferromagnetism on the facets! (111) ( 100 )
14 2. Scientific cases: A. Anomalous Palladium magnetism in nanostructures Techniques: HRTEM, SQUID Ferromagnetism due to defects (stacking faults)!
15 2A. Palladium magnetism: Stoner Criterion for Magnetism of Conduction Electrons Energetically favorable Stoner Criterion:
16 2A. Palladium magnetism: Stoner Criterion for Magnetism of Conduction Electrons DOS at the Fermi Energy Iron Almost... Palladium
17 2A. Observation of Ferromagnetism in PdCo nanoparticles encapsulated in Carbon Nanotubes 2um Técnica de crescimento: Deposição Química na Fase Vapor Assistida por Plasma PECVD. - Alto controle; - Alinhamento vertical. Distribuição de tamanho: Diâmetro = (79_+ 30)nm
18 2A. Observation of Ferromagnetism in PdCo em nanoparticles encapsulated in Carbon Nanotubes Microscopia Eletrônica de Transmissão (TEM) Homogeneidade da amostra; Anisotropia de forma das partículas; Estrutura cristalina: PdCo (fcc) próxima a do Paládio bulk. Concentração de Pd em relação ao Co ao longo da partícula é aproximadamente constante
19 2A. Observation of Ferromagnetism in PdCo em nanoparticles encapsulated in Carbon Nanotubes Magnetometria de amostra vibrante (VSM) Comportamento magnético global da amostra; Temperatura ambiente; Campo de saturação: 1500 Oe Anisotropia magnética uniaxial: - eixo duro: H perpendicular; - eixo fácil: H longitudinal. H longitudinal
20 2A. A. Observation of Ferromagnetism in PdCo em nanoparticles encapsulated in Carbon Nanotubes Magnetometria de amostra vibrante (VSM) Comportamento magnético global da amostra; Temperatura ambiente; Campo de saturação: 1500 Oe Anisotropia magnética uniaxial: - eixo duro: H perpendicular; - eixo fácil: H longitudinal. H longitudinal
21 2A. Observation of Ferromagnetism in PdCo em nanoparticles encapsulated in Carbon Nanotubes Easy axis Longitudinal: easy axis Perpendicular: hard axis longitudinal perpendicular Hard axis H longitudinal Second derivative: Removing paramagnetic signal Hc = 1500Oe
22 Norm. Intensity Norm. Intensity Norm. Intensity 2A. Observation of Ferromagnetism in PdCo em nanoparticles encapsulated in Carbon Nanotubes Pd/Co: 4/0.5nm Pd/Co:4/1nm Pd /Co:4/4nm 1,0 1,0 1,0 0,5 Hr < 60 Oe longitudinal perpendicular 0,5 Hr < 60 Oe longitudinal perpendicular 0,5 Hr ~ 600 Oe 1000 Oe longitudinal perpendicular 0,0 0,0 0,0-0,5-1,0 Não apresenta anisotropia -0,5-1,0 Não apresenta anisotropia -0,5-1,0 Anisotropia evidente H (Oe) H (Oe) H (Oe)
23 2A. X-ray magnetic circular dichroism of PdCo nanoparticles XMCD at LNLS Informação magnética com informação química-estrutural! Temperatura ambiente; LNLS, linhas de luz: bordas L 2 e L 3 Co PGM ( ev); Pd SXS ( eV); Campo magnético aplicado: ~10000 Oe (1 T) <6x o necessário
24 2A. Observation of Ferromagnetism in PdCo em nanoparticles encapsulated in Carbon Nanotubes Dicroísmo Circular Magnético de Raios-X (XMCD) Cobalto: Paládio: Cobalto bulk: 0,099
25 2. Scientific cases: B. Room temperature observation of orbital momentum enhancement of Co nanoclusters grown on Au(110) Low dimensional systems (nanoparticles, clusters, 1d systems) exhibit anomalous magnetic behavior) Techniques: STM (for size determination) SQUID (for magnetism) XMCD (orbital and spin 5 Kelvin, 8 Tesla!!! momentum)
26 XMCD at LNLS New Beamline PGM EPU-type Undulator beamline VLS PGM monochromator Polarized soft-x-rays Energy = eV Applications: X-ray magnetic circular dichroism X-ray photoelectron Difraction X-ray photoelectron Spectroscopy Electron spectroscopy of liquids Among others...
27 Test experiment: Magnetism of Cobalt nanoparticles grown on Au (110) Preparation of Au(110) surface (2x1) reconstruction observed by lowenergy electron diffraction) Surface prepared by 1.5 KeV Ar+ sputtering, 400 o C annealing, P base =2 x mbar Asymmetric deposition of Cobalt Cobalt e-beam source Variable size Co clusters Au(110)
28 Preparation experiment at DF-UFMG: STM and LEED of Au(110) and 4 ml Co/Au(110)
29 XMCD of Cobalt nanoparticles grown on Au (110) First measurement of systems of low dimensionality Room temperature Applied magnetic field 1.6 Tesla Beamline PGM -LNLS, Cobalt L 2 e L 3 Edges PGM ( ev);
30 X-ray absorption spectroscopy of Cobalt nanoparticles grown on Au (110) L 3 L 2
31 XMCD of Cobalt nanoparticles grown on Au (110) The equivalent of 4 monolayers of Cobalt were deposited L 3 L 2 Dichroism is evident
32 Determination of orbital moments is possible if magnetization is not saturated Pol 1 x cosq m B 1 Pol Pol x cosq Determination of q using m spin = 2.14 m B m spin + m orb q B ext Cobalt coverage (ml) B ext =1.6Tesla T=300K
33 Determination of orbital and spin moments is not possible if magnetization is not saturated Low temperature (5Kelvin) Room temperature (300Kelvin) L 3 L 2
34 Large orbital momentum of Cobalt nanoparticles m L (bulk Co) 0.2 Au(110) High coordination Number m L 0
35 Large orbital momentum of Cobalt nanoparticles m L (bulk Co) 0.2 Au(110) High coordination Number m L 0
36 2C. Magnetic domain reconfiguration in MnAs/GaAs(001) films 38 0 C 30 o C 34 0 C Atomic Force Microscopy (Topography) 34 o C 30 0 C Magnetic Force Microscopy (Magnetic Boundaries) 25 0 C MFM - The magnetic profile changes at about T = 31ºC: Meanders Line-shaped structures
37 Intensity a.u. L (nm) Intensity (arb. units) 2C. Magnetic domain reconfiguration in MnAs/GaAs(001) films: Terrace structure H q x : terraces period; q z : terraces height; Elastic scattering: Rocking scans s = 642nm d =130nm Terraces Scattering s 2 q x q x (nm -1 ) 0 Temperature ( o C) K 318 K 308 K 298 K 288 K q x (nm -1 ) 278 K Appl. Phys. Lett. (2005)
38 Intensity a.u. Reflectivity u.a. 2C. Magnetic domain reconfiguration in MnAs/GaAs(001) films X-Ray Magnetic Resonant Scattering: Polarization and Energy Near the ressonance, charge scattering increases considerably. Magnetic effects are noticeable, as large as 7% at the Mn L III edge (639eV) Mn L III edge ~ 639eV Mag - Mag + Difference Mn L II edge ~ 650eV 0 Depending on the polarization, different magnetization directions are probed Energy (ev) 160 First order Bragg Polarization peak due to C the terraces C + T=288K q x (nm -1 )
39 Intensity a.u. Intensity a.u. 2C. MnAs/GaAs(001) films: terrace structure and Magnetic Hysteresis measured by resonant magnetic X-ray scattering K 304K 298K 297K 296K 294K 292K 291K 290K Change in hysteresis lineshape!!! q x (nm -1 ) Magnetic field (Oe) Hysteresis and rocking curves were done as function of temperature.
40 2C. MnAs/GaAs(001) films: Magnetic Hysteresis measured by resonant magnetic X-ray scattering Shrinking of ferromagnetic terrace Reconfiguration of magnetic domains H ext Magnetic field (Oe)
41 2C. Magnetic force micorsopy of MnAs/GaAs(001) film Shrinking of magnetic terrace Reconfiguration of magnetic domains! Thermodynamic model of magnetic reconfiguration (p = 2.6) (J. Appl. Phys. 2006) Calculation of demagnetization energy
42 2C. MnAs/GaAs(001) films: Magnetic Hysteresis measured by resonant magnetic X-ray scattering Thermodynamic model of magnetic reconfiguration (J. Appl. Physics 2006)
43 2D. Fe/MnAs films: chemical sensitivity using resonant magnetic X-ray scattering Mn L 3 edge 640eV, Fe L 3 edge 707eV
44 D. Fe/MnAs films: magnetic hysteresis measured by magnetic resonant X- ray scattering. Each scans is performed at two different absorption edges: Fe and Mn!!! Mn 640eV Fe 707eV
45 2D. Fe/MnAs films: Magnetic Hysteresis measured by resonant magnetic X-ray scattering: magnetic coupling between MnAs teraces and Fe film C 22 0 C 27 0 C 30 0 C Can we make a thermodynamic model of magnetic reconfiguration (current research)?
46 2E. Microscopy with magnetic domain sensitivity Ferromagnetic domain pattern for a thin Co layer on NiO(100), showing all four spin directions in Co. The spin directions are pinned by the underlying NiO.
47 4. Conclusions X-ray magnetic circular dichroism reveals magnetism with chemical specificity Orbital and spin moments can be determined separately - Anomalous Palladium magnetism in nanostructures - Giant orbital magnetic moment of Co/Au nanostructures - Magnetic domain reconfiguration in MnAs/GaAs films - Fe/MnAs magnetic coupling - Microscopy with magnetic domain sensitivity
48 Acknowledgements Daniel Bretas, Letícia Coelho (DF-UFMG) Harry Westfahl (LNLS, Campinas) Maurizio Sacchi (SOLEIL, France) Thanks: ABTLuS, CNPq, FAPESP, FAPEMIG
Properties of Electrons, their Interactions with Matter and Applications in Electron Microscopy By Frank Krumeich Laboratory of Inorganic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland
Chem. Rev. 2005, 105, 1103 1169 1103 Self-Assembled Monolayers of Thiolates on Metals as a Form of Nanotechnology J. Christopher Love, Lara A. Estroff, Jennah K. Kriebel, Ralph G. Nuzzo,*, and George M.
Ž. Diamond and Related Materials 11 2002 16 21 Plasma enhanced deposition of silicon carbonitride thin films and property characterization Z.X. Cao National Laboratory for Surface Physics, Institute of
Magnetism research with polarized neutrons at the Centro di Studi Nucleari della Casaccia del C. N. E. N., Roma, Italy B. Antonini, G.P. Felcher, F. Menzinger, A. Paoletti, F.P. Ricci, L. Passari To cite
The plasmoelectric effect: optically induced electrochemical potentials in resonant metallic structures Matthew T. Sheldon and Harry A. Atwater Thomas J. Watson Laboratories of Applied Physics, California
Diamond and Related Materials 11 (00) 1041 1046 Deposition and properties of amorphous carbon phosphide films a a, b b b S.R.J. Pearce, P.W. May *, R.K. Wild, K.R. Hallam, P.J. Heard a School of Chemistry,
J. Phys.: Condens. Matter 12 (2000) 189 199. Printed in the UK PII: S0953-8984(00)06853-3 Photochromism of vacancy-related centres in diamond K Iakoubovskii, G J Adriaenssens and M Nesladek Laboratorium
Learning Objectives for AP Physics These course objectives are intended to elaborate on the content outline for Physics B and Physics C found in the AP Physics Course Description. In addition to the five
Synthesis of mesoporous silica particles with control of both pore diameter and particle size Master of Science Thesis in Materials and Nanotechnology program ALBERT BARRABINO Department of Chemical and
Lecture 6 Scanning Tunneling Microscopy (STM) General components of STM; Tunneling current; Feedback system; Tip --- the probe. Brief Overview of STM Inventors of STM The Nobel Prize in Physics 1986 Nobel
Magnetic dynamics driven by spin current Sergej O. Demokritov University of Muenster, Germany Giant magnetoresistance Spin current Group of NonLinear Magnetic Dynamics Charge current vs spin current Electron:
Man et al. Nanoscale Research Letters (2015) 10:279 DOI 10.1186/s11671-015-0974-4 NANO EXPRESS Graphene-Based Flexible and Transparent Tunable Capacitors Open Access Baoyuan Man 1*,ShicaiXu 1,2, Shouzheng
1 Symmetry-operations, point groups, space groups and crystal structure KJ/MV 210 Helmer Fjellvåg, Department of Chemistry, University of Oslo 1994 This compendium replaces chapter 5.3 and 6 in West. Sections
Single-Electron Devices and Their Applications KONSTANTIN K. LIKHAREV, MEMBER, IEEE Invited Paper The goal of this paper is to review in brief the basic physics of single-electron devices, as well as their
Optimization of open circuit voltage in amorphous silicon solar cells with mixed-phase amorphous+ nanocrystalline p-type contacts of low nanocrystalline content J. M. Pearce a Physics Department, Clarion
Non-Volatile Memory Based on Solid Electrolytes Michael N. Kozicki, Chakravarthy Gopalan, Murali Balakrishnan, Mira Park, and Maria Mitkova Center for Solid State Electronics Research Arizona State University
About the Department of Energy s Basic Energy Sciences Program Basic Energy Sciences (BES) supports fundamental research to understand, predict, and ultimately control matter and energy at the electronic,
LHC Project Note 78 / 97 January 18, 1997 firstname.lastname@example.org On Graphite Transformations at High Temperature and Pressure Induced by Absorption of the LHC Beam Jan M. Zazula CERN-SL/BT(TA) Keywords: Summary
One-Dimensional Nanostructures: Synthesis, Characterization, and Applications** By Younan Xia,* Peidong Yang,* Yugang Sun, Yiying Wu, Brian Mayers, Byron Gates, Yadong Yin, Franklin Kim, and Haoquan Yan
SEMICONDUCTORS AND SEMIMETALS VOL 35 CHAPTER 2 Quantum Point Contacts H. van Hauten and C. W. J. Beenakker PHILIPS RESEARCH LABORATORIES EINDHOVEN THE NETHERL \NDS B J. van Wees DEPARTMENT OE APPLIED PHYSICS
TRANSACTIONS ON ELECTRICAL AND ELECTRONIC MATERIALS Vol. 16, No. 2, pp. 90-94, April 25, 2015 Regular Paper pissn: 1229-7607 eissn: 2092-7592 DOI: http://dx.doi.org/10.4313/teem.2015.16.2.90 OAK Central:
Università degli Studi Roma TRE e Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia Dottorato di Ricerca in Scienze Fisiche della Materia XXIII ciclo Challenges for first principles
BACKGROUND INFORMATION Infrared Spectroscopy Before introducing the subject of IR spectroscopy, we must first review some aspects of the electromagnetic spectrum. The electromagnetic spectrum is composed
Contents Which functional should I choose? Dmitrĳ Rappoport, Nathan R. M. Crawford, Filipp Furche, and Kieron Burke December 15, 2008 5 Various directions in DFT development 29 5.1 Semi-local functionals................
Journal of Microscopy, Vol. 215, Pt 1 July 2004, pp. 13 23 Received 26 March 2003; accepted 5 January 2004 Quantitative analysis and classification of AFM images of Blackwell Publishing, Ltd. human hair
32. Passage of particles through matter 1 32. PASSAGE OF PARTICLES THROUGH MATTER...................... 2 32.1. Notation.................... 2 32.2. Electronic energy loss by heavy particles...... 2 32.2.1.