Room Temperature Hyperpolarization of Nuclear Spins in Bulk
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S-Electron Ferromagnetism in Gold and Silver Nanoclusters
NANO LETTERS 2007 s-Electron Ferromagnetism in Gold and Vol. 7, No. 10 Silver Nanoclusters 3134-3137 Weidong Luo,*,†,‡ Stephen J. Pennycook,‡ and Sokrates T. Pantelides†,‡ Department of Physics and Astronomy, Vanderbilt UniVersity, NashVille, Tennessee 37235, and Materials Science and Technology DiVision, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 Received July 12, 2007 ABSTRACT Ferromagnetic (FM) ordering in transition-metal systems (solids, surface layers, nanoparticles) arises from partially filled d shells. Thus, recent observations of FM Au nanoclusters was unexpected, and an explanation has remained elusive. Here we report first-principles density- functional spin-polarized calculations for Au and Ag nanoclusters. We find that the highest-occupied level is highly degenerate and partially filled by s electrons with spins aligned according to Hund’s rule. The nanoclusters behave like “superatoms”, with the spin-aligned electrons being itinerant on the outer shell of atoms. Ferromagnetism in bulk Fe, Co, and Ni originates from shells is crucial to achieve FM ordering. The case of Au partially filled 3d shells. In contrast, transition metals in the nanoparticles is particularly intriguing because the d orbitals 4d and 5d series do not exhibit FM ordering. The difference are completely full and bulk Au is diamagnetic. Hori et al.8,9 has been explained by the Stoner theory of itinerant electron reported that Au nanoparticles capped by a polymer exhibit magnetism.1 A combination of large density-of-states at the ferromagnetism (the presence of transition-metal impurities Fermi energy, NF, and a large Stoner exchange constant I is with partially filled d shells was ruled out), whereas Crespo essential. -
Magnetism on the Nanoscale I
Joseph Dufouleur, Quantum Transport Group, [email protected] Magnetism on the nanoscale I. What is spintronics? 1. A brief introduction Conventional electronic: manipulate the charge of the electron. One of the most important technological projection of the second half of the 20th century. Few decades after the discovery of the transistor (1947) ⇓ manipulate the spin of the charge carrier instead of its charge: ⟶ improve many different properties of the electronic/spintronc devices ⟶ explore new functionalities of spintronic devices. For instance: •using ferromagnet-based electronics ⟶ very stable memory (M-RAM) and devices with very fast switching properties. •It was demonstrated that heterostructures of semiconductors and ferromagnetic metals can be used to build a spin-polarized light emitting diode. •As a prospective aim: spin transistor: (https://slideplayer.com/slide/5189531/) •to be able to manipulate one single spin as a q-bit would be a great achievement on the way of building a quantum computer. commercial applications following discoveries in spintronics field: •GMR (Fert and Grünberg, Nobel prize in 2007) or TMR: Magnetic field sensors. In 2008, the term GMR appeared in more than 1500 US patents! •TMR: Read heads of magnetic hard disk drives and non-volatils random access memory. •Spin injection -> polarized LED, ... Principle: interaction ferromagnet spin of the conduction electrons - spin polarized a current (spin injection) - orientation of the magnetization determine the current flow ie. the resistance - the current flow can influence the orientation of the magnetization -> „Spin transfer torque“ Key points for building spintronic devices: • To be able to inject spins into a device or, equivalently, to create a spin current by polarizing for instance a charge current. -
Direct Observation of High Spin Polarization in Co2feal Thin Films
www.nature.com/scientificreports OPEN Direct observation of high spin polarization in Co2FeAl thin flms Xiaoqian Zhang1, Huanfeng Xu1, Bolin Lai1, Qiangsheng Lu2,3, Xianyang Lu 4, Yequan Chen1, Wei Niu1, Chenyi Gu5, Wenqing Liu1,4, Xuefeng Wang 1, Chang Liu2, Yuefeng Nie5, Liang He1 1,4 Received: 11 December 2017 & Yongbing Xu Accepted: 3 April 2018 We have studied the Co2FeAl thin flms with diferent thicknesses epitaxially grown on GaAs (001) by Published: xx xx xxxx molecular beam epitaxy. The magnetic properties and spin polarization of the flms were investigated by in-situ magneto-optic Kerr efect (MOKE) measurement and spin-resolved angle-resolved photoemission spectroscopy (spin-ARPES) at 300 K, respectively. High spin polarization of 58% (±7%) was observed for the flm with thickness of 21 unit cells (uc), for the frst time. However, when the thickness decreases to 2.5 uc, the spin polarization falls to 29% (±2%) only. This change is also accompanied by a magnetic transition at 4 uc characterized by the MOKE intensity. Above it, the flm’s magnetization reaches the bulk value of 1000 emu/cm3. Our fndings set a lower limit on the thickness of Co2FeAl flms, which possesses both high spin polarization and large magnetization. Spintronic devices rely on thin layers of magnetic materials, for they are designed to control both the charge and the spin current of the electrons. Half-metallic ferromagnets (HMFs) have only one spin channel for conduction at the Fermi level, while they have a band gap in the other spin channel1–4. Terefore, in principle this kind of material has 100% spin polarization for transport, which is perfect for spin injection, spin fltering, and spin trans- fer torque devices5. -
Effect of Spin Polarization on the Structural Properties and Bond Hardness of Fexb(X = 1, 2, 3) Compounds first-Principles Study
Bull. Mater. Sci., Vol. 39, No. 6, October 2016, pp. 1427–1434. c Indian Academy of Sciences. DOI 10.1007/s12034-016-1263-2 Effect of spin polarization on the structural properties and bond hardness of FexB(x = 1, 2, 3) compounds first-principles study AHMED GUEDDOUH1,2,∗, BACHIR BENTRIA1, IBN KHALDOUN LEFKAIER1 and YAHIA BOUROUROU3 1Laboratoire de Physique des Matériaux, Université Amar Telidji de Laghouat, BP37G, Laghouat 03000, Algeria 2Département de Physique, Faculté des Sciences, Université A.B. Belkaid Tlemcen, BP 119, Tlemcen 13000, Algeria 3Modeling and Simulation in Materials Science Laboratory, University of Sidi Bel-Abbès, 22000 Sidi Bel-Abbès, Algeria MS received 14 November 2014; accepted 17 March 2016 Abstract. In this paper, spin and non-spin polarization (SP, NSP) are performed to study structural properties and bond hardness of Fex B(x = 1, 2, 3) compounds using density functional theory (DFT) within generalized gradient approximation (GGA) to evaluate the effect of spin polarization on these properties. The non-spin-polarization results show that the non-magnetic state (NM) is less stable thermodynamically for Fex B compounds than spin- polarization by the calculated cohesive energy and formation enthalpy. Spin-polarization calculations show that ferromagnetic state (FM) is stable for Fex B structures and carry magnetic moment of 1.12, 1.83 and 2.03 μBinFeB, Fe2BandFe3B, respectively. The calculated lattice parameters, bulk modulus and magnetic moments agree well with experimental and other theoretical results. Significant differences in volume and in bulk modulus were found between the ferromagnetic and non-magnetic cases, i.e., 6.8, 32.8%, respectively. -
Spin-Polarized Exotic Nuclei
Spin-polarized exotic nuclei: from fundamental interactions, via nuclear structure, to biology and medicine Magdalena Kowalska UNIGE and CERN Outline Decay of polarized nuclei Spin polarization with lasers Spin-polarized radioactive nuclei in: Fundamental physics Nuclear physics NMR in biology MRI in medicine Summary and outlook 2 Decay of spin-polarized nuclei Beta and gamma decay of spin-polarized nuclei anisotropic in space Beta decay, I>0 Gamma decay, I>1/2 B0 푊 휃푟 = 1 + 푎1cos(휃푟) a1=P ab depend on degree and order of spin polarization and transition details (initial spin, change of spin) Observed decay asymmetry can be used to: Probe underlying decay mechanism (GT) Determine properties of involved nuclear states Derive differences in nuclear energy levels3 Spin polarization via optical pumping Multiple excitation cycles with circularly-polarized laser light Photon angular momentum transferred to electrons and then nuclei Works best for 1 valence electron nuclear spin-polarization of 10-90% Polarization buildup time < us fine structure hyperfine structure Magnetic sublevels 3p 2P 3 -3 -2 -1 0 1 2 3 3/2 2 1 0 F 29Mg + I =3/2 D2-line s+ light 2 -2 -1 0 1 2 2 3s S1/2 1 frequency 4 Optical pumping and nuclear spins Polarization of atomic spins leads to polarization of nuclear spins via hyperfine interaction (PF->PI) Decoupling of electron (J) and nuclear (I) spins in strong magnetic field Observation of nuclear spin polarization PI possible Magnetic field B 3p 2P 3 3/2 2 1 0 Dm = +1 for s+ or -1 for s- light 29Mg F I =3/2 3/2 -
Dynamic Nuclear Polarization for Magnetic Resonance Imaging: an In-Bore Approach
Dynamic Nuclear Polarization for Magnetic Resonance Imaging: An In-bore Approach Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften vorgelegt beim Fachbereich 14 der Johann Wolfgang Goethe-Universit¨at in Frankfurt am Main von Jan G. Krummenacker aus V¨olklingen Frankfurt, 2012 D30 vom Fachbereich 14 der Johann-Wolfgang Goethe-Universit¨atals Dissertation angenommen. Dekan: Prof. Dr. Thomas F. Prisner Gutachter: Prof. Dr. Thomas F. Prisner, Prof. Dr. Laura M. Schreiber Datum der Disputation: Contents 1 Introduction 7 2 Theoretical Background 11 2.1 NMR Basics . 11 2.1.1 The Zeeman Term: Thermal Polarization . 12 2.1.2 Magnetization . 15 2.1.3 The RF Term: Manipulation of Magnetizations . 16 2.1.4 The Bloch Equations . 17 2.1.5 NMR Experiments . 18 2.2 EPR Basics . 21 2.2.1 EPR Spectrum of TEMPOL . 23 2.3 Dynamic Nuclear Polarization . 25 2.3.1 The Overhauser Effect . 25 2.3.2 Leakage Factor . 28 2.3.3 Saturation Factor . 29 2.3.4 Coupling Factor . 31 2.3.5 DNP in Solids . 34 3 Liquid State DNP at High Fields 37 3.1 Hardware . 37 3.1.1 The DNP Spectrometer . 38 3.1.2 Microwave Sources . 40 3.1.3 Power Transmission . 41 3.1.4 Experimental Procedures . 41 3.2 Experimental Results . 43 3.2.1 DNP on Water . 43 3.2.2 DNP on Organic Solvents . 53 3.2.3 Beyond Solvents: DNP on Metabolites . 56 3.3 Conclusion and Outlook . 62 3 4 CONTENTS 4 DNP for MRI 63 4.1 Other Hyperpolarization Methods . 63 4.1.1 PHIP . -
Some Polarized Target Experiments for Elementary Particle Physics
SOME POLARIZED TARGET EXPERIMENTS FOR ELEMENTARY PARTICLE PHYSICS R.H. DALITZ Department of Theoretical Physics, Oxford INTRODUCTION At the present stage in elementary particle physics, there are three major areas of phenomena where the use of polarized targets may lead to especially illuminating information. a. High energy scattering, in the energy range where the dominant contributions to the processes observed may arise from Reggion ex change. The features of particular interest in these situjtions will be discussed at this meeting by Dr R.J.N. Phillips 1 • b. Tests of time-reversal (T) invariance for electrom~gnetic pro cesses, following the suggestion by Bernstein et al 2) that the CF-violation observed in the weak decay of kaons arises from the existence of an electromagnetic interaction which strongly viola tes T-invariance. Evidence for this hypothetical T-violating elec tromagnetic interaction can be sought most directly in the study of electromagnetic processes from a polarized proton target, for example in the study of the electro-excitation process e + N-+ e + N* , as discussed by Christ and Lee 3J. The experi~ents proposed will be discussed at this meeting by Dr M. Jacob 4J. c. Hadron spectroscopy. Very many resonant states have been obser ved for masonic and baryonic states. These hadronic states are be lieved to correspond to the patterns appropriate to unitary multi plets of states, and these unitary multiplets appear to be grouped in supermultiplet patterns. In our attempt to classify and under stand all these hadronic states, our first need is for the deter mination of the spin and parity for each state. -
A Peek Into Spin Physics
A Peek into Spin Physics Dustin Keller University of Virginia Colloquium at Kent State Physics Outline ● What is Spin Physics ● How Do we Use It ● An Example Physics ● Instrumentation What is Spin Physics The Physics of exploiting spin - Spin in nuclear reactions - Nucleon helicity structure - 3D Structure of nucleons - Fundamental symmetries - Spin probes in beyond SM - Polarized Beams and Targets,... What is Spin Physics What is Spin Physics ● The Physics of exploiting spin : By using Polarized Observables Spin: The intrinsic form of angular momentum carried by elementary particles, composite particles, and atomic nuclei. The Spin quantum number is one of two types of angular momentum in quantum mechanics, the other being orbital angular momentum. What is Spin Physics What Quantum Numbers? What is Spin Physics What Quantum Numbers? Internal or intrinsic quantum properties of particles, which can be used to uniquely characterize What is Spin Physics What Quantum Numbers? Internal or intrinsic quantum properties of particles, which can be used to uniquely characterize These numbers describe values of conserved quantities in the dynamics of a quantum system What is Spin Physics But a particle is not a sphere and spin is solely a quantum-mechanical phenomena What is Spin Physics Stern-Gerlach: If spin had continuous values like the classical picture we would see it What is Spin Physics Stern-Gerlach: Instead we see spin has only two values in the field with opposite directions: or spin-up and spin-down What is Spin Physics W. Pauli (1925) -
Analysis of Spin Polarization in Half-Metallic Heusler Alloys
Macalester Journal of Physics and Astronomy Volume 3 Issue 1 Spring 2015 Article 3 May 2015 Analysis of Spin Polarization in Half-Metallic Heusler Alloys Alexandra McNichol Boldin Macalester College, [email protected] Follow this and additional works at: https://digitalcommons.macalester.edu/mjpa Part of the Condensed Matter Physics Commons Recommended Citation Boldin, Alexandra McNichol (2015) "Analysis of Spin Polarization in Half-Metallic Heusler Alloys," Macalester Journal of Physics and Astronomy: Vol. 3 : Iss. 1 , Article 3. Available at: https://digitalcommons.macalester.edu/mjpa/vol3/iss1/3 This Capstone is brought to you for free and open access by the Physics and Astronomy Department at DigitalCommons@Macalester College. It has been accepted for inclusion in Macalester Journal of Physics and Astronomy by an authorized editor of DigitalCommons@Macalester College. For more information, please contact [email protected]. Analysis of Spin Polarization in Half-Metallic Heusler Alloys Abstract Half-metals have recently gained great interest in the field of spintronics because their 100% spin polarization may make them an ideal current source for spintronic devices. This project examines four Heusler Alloys of the form Co2FexMn1−xSi that are expected to be half-metallic. Two magnetic properties of these alloys were examined, the Anisotropic Magnetoresistance (AMR) and the Anomalous Hall Effect (AHE). These properties have the potential to be used as simple and fast ways to identify materials as half-metallic or non-half-metallic. The results of these measurements were also used to examine the spin polarization and other properties of these materials. This capstone is available in Macalester Journal of Physics and Astronomy: https://digitalcommons.macalester.edu/ mjpa/vol3/iss1/3 Boldin: Analysis of Spin Polarization in Half-Metallic Heusler Alloys I. -
Polarized Target for the Measurement of the Gluon Contribution to the Nucleon Spin in the COMPASS Experiment
Polarized target for the measurement of the gluon contribution to the nucleon spin in the COMPASS experiment Nagoya University Thesis for the degree Doctor of Philosophy in Physics by Naoki TAKABAYASHI 1 2002 1 Supported by Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists. CONTENTS 1. Introduction : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 1 2. Spin structure of the nucleon : : : : : : : : : : : : : : : : : : : : : 5 2.1 Deep inelastic scattering . 5 2.2 Cross section and structure functions in unpolarized DIS . 7 2.3 Cross section and structure functions in polarized DIS . 9 2.4 Structure functions and spin puzzle in Parton Model picture . 13 2.4.1 Parton distribution . 14 2.4.2 Spin puzzle in Parton Model picture . 16 2.5 Structure functions and spin puzzle in QCD evolved Parton Model . 18 2.5.1 Unpolarized structure functions . 18 2.5.2 Factorization schemes . 20 2.5.3 DGLAP equation and Scaling violation . 22 2.5.4 Spin-dependent structure functions and polarized DGLAP equation . 23 2.6 Interpretation of small ∆Σ. Is gluon contribution large? . 24 2.6.1 Sum rules . 25 2.6.2 Axial anomaly . 26 3. COMPASS experiment : : : : : : : : : : : : : : : : : : : : : : : : : 30 3.1 Open charm lepto-production via photon-gluon fusion . 30 3.2 Expectations . 35 3.2.1 Luminosity . 35 3.2.2 Reconstruction of the open charm events . 35 3.2.3 Statistical accuracy . 37 3.3 Comparison with the other experiments on ∆g . 40 3.3.1 High pT hadron pairs . 40 3.3.2 pp¯ collision . 41 3.3.3 Comparison of the expected precisions and the kine- matic ranges . -
Hadron Spin Dynamics∗
SLAC-PUB-9107 January 2002 Hadron Spin Dynamics¤ Stanley J. Brodsky Stanford Linear Accelerator Center, Stanford University Stanford, California 94309 e-mail: [email protected] Abstract Spin effects in exclusive and inclusive reactions provide an essential new dimension for testing QCD and unraveling hadron structure. Remarkable new experiments from SLAC, HERMES (DESY), and Jefferson Lab present many challenges to theory, including measurements at HERMES and SMC of the sin- gle spin asymmetries in ep ! e0¼X where the proton is polarized normal to the scattering plane. This type of single spin asymmetry may be due to the effects of rescattering of the outgoing quark on the spectators of the target proton, an effect usually neglected in conventional QCD analyses. Many aspects of spin, such as single-spin asymmetries and baryon magnetic moments are sensitive to the dynamics of hadrons at the amplitude level, rather than probability dis- tributions. I will illustrate the novel features of spin dynamics for relativistic systems by examining the explicit form of the light-front wavefunctions for the two-particle Fock state of the electron in QED, thus connecting the Schwinger anomalous magnetic moment to the spin and orbital momentum carried by its Fock state constituents and providing a transparent basis for understand- ing the structure of relativistic composite systems and their matrix elements in hadronic physics. I also present a survey of outstanding spin puzzles in QCD, particularly ANN in elastic pp scattering, the J=Ã ! ½¼ puzzle, and J=Ã polarization at the Tevatron. Concluding Theory Talk, presented at the 3rd Circum-Pan-Pacific Symposium On High Energy Spin Physics (SPIN 2001) Beijing, China 8–13 October 2001 ¤Work supported by the Department of Energy, contract DE–AC03–76SF00515. -
Magnetic Generation of Normal Pseudo-Spin Polarization In
www.nature.com/scientificreports OPEN Magnetic generation of normal pseudo‑spin polarization in disordered graphene R. Baghran 1, M. M. Tehranchi 1* & A. Phirouznia 2,3 Spin to pseudo‑spin conversion by which the non‑equilibrium normal sublattice pseudo‑spin polarization could be achieved by magnetic feld has been proposed in graphene. Calculations have been performed within the Kubo approach for both pure and disordered graphene including vertex corrections of impurities. Results indicate that the normal magnetic feld Bz produces pseudo‑spin polarization in graphene regardless of whether the contribution of vertex corrections has been taken into account or not. This is because of non‑vanishing correlation between the σz and τz provided by the co‑existence of extrinsic Rashba and intrinsic spin–orbit interactions which combines normal spin and pseudo‑spin. For the case of pure graphene, valley‑symmetric spin to pseudo‑spin response function is obtained. Meanwhile, by taking into account the vertex corrections of impurities the obtained response function is weakened by several orders of magnitude with non‑identical contributions of diferent valleys. This valley‑asymmetry originates from the inversion symmetry breaking generated by the scattering matrix. Finally, spin to pseudo‑spin conversion in graphene could be realized as a practical technique for both generation and manipulation of normal sublattice pseudo‑spin polarization by an accessible magnetic feld in a easy way. This novel proposed efect not only ofers the opportunity to selective manipulation of carrier densities on diferent sublattice but also could be employed in data transfer technology. The normal pseudo‑spin polarization which manifests it self as electron population imbalance of diferent sublattices can be detected by optical spectroscopy measurements.