Exchange Interactions and Curie Temperature of Ce-Substituted Smco5
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
Unerring in Her Scientific Enquiry and Not Afraid of Hard Work, Marie Curie Set a Shining Example for Generations of Scientists
Historical profile Elements of inspiration Unerring in her scientific enquiry and not afraid of hard work, Marie Curie set a shining example for generations of scientists. Bill Griffiths explores the life of a chemical heroine SCIENCE SOURCE / SCIENCE PHOTO LIBRARY LIBRARY PHOTO SCIENCE / SOURCE SCIENCE 42 | Chemistry World | January 2011 www.chemistryworld.org On 10 December 1911, Marie Curie only elements then known to or ammonia, having a water- In short was awarded the Nobel prize exhibit radioactivity. Her samples insoluble carbonate akin to BaCO3 in chemistry for ‘services to the were placed on a condenser plate It is 100 years since and a chloride slightly less soluble advancement of chemistry by the charged to 100 Volts and attached Marie Curie became the than BaCl2 which acted as a carrier discovery of the elements radium to one of Pierre’s electrometers, and first person ever to win for it. This they named radium, and polonium’. She was the first thereby she measured quantitatively two Nobel prizes publishing their results on Boxing female recipient of any Nobel prize their radioactivity. She found the Marie and her husband day 1898;2 French spectroscopist and the first person ever to be minerals pitchblende (UO2) and Pierre pioneered the Eugène-Anatole Demarçay found awarded two (she, Pierre Curie and chalcolite (Cu(UO2)2(PO4)2.12H2O) study of radiactivity a new atomic spectral line from Henri Becquerel had shared the to be more radioactive than pure and discovered two new the element, helping to confirm 1903 physics prize for their work on uranium, so reasoned that they must elements, radium and its status. -
Magnetism, Magnetic Properties, Magnetochemistry
Magnetism, Magnetic Properties, Magnetochemistry 1 Magnetism All matter is electronic Positive/negative charges - bound by Coulombic forces Result of electric field E between charges, electric dipole Electric and magnetic fields = the electromagnetic interaction (Oersted, Maxwell) Electric field = electric +/ charges, electric dipole Magnetic field ??No source?? No magnetic charges, N-S No magnetic monopole Magnetic field = motion of electric charges (electric current, atomic motions) Magnetic dipole – magnetic moment = i A [A m2] 2 Electromagnetic Fields 3 Magnetism Magnetic field = motion of electric charges • Macro - electric current • Micro - spin + orbital momentum Ampère 1822 Poisson model Magnetic dipole – magnetic (dipole) moment [A m2] i A 4 Ampere model Magnetism Microscopic explanation of source of magnetism = Fundamental quantum magnets Unpaired electrons = spins (Bohr 1913) Atomic building blocks (protons, neutrons and electrons = fermions) possess an intrinsic magnetic moment Relativistic quantum theory (P. Dirac 1928) SPIN (quantum property ~ rotation of charged particles) Spin (½ for all fermions) gives rise to a magnetic moment 5 Atomic Motions of Electric Charges The origins for the magnetic moment of a free atom Motions of Electric Charges: 1) The spins of the electrons S. Unpaired spins give a paramagnetic contribution. Paired spins give a diamagnetic contribution. 2) The orbital angular momentum L of the electrons about the nucleus, degenerate orbitals, paramagnetic contribution. The change in the orbital moment -
Effective Medium Theory of Magnetization Reversal in Magnetically Interacting Particles Heliang Qu and Jiangyu Li
IEEE TRANSACTIONS ON MAGNETICS, VOL. 41, NO. 3, MARCH 2005 1093 Effective Medium Theory of Magnetization Reversal in Magnetically Interacting Particles Heliang Qu and JiangYu Li Abstract—We report an effective medium theory of magnetiza- One of the breakthroughs was made about ten years ago tion reversal and hysteresis in magnetically interacting particles, when an exchange coupling mechanism was proposed to en- where the intergranular magnetostatic interaction is accounted hance the energy product of permanent magnets [3]. The idea for by an effective medium approximation. We introduce two is to mix the magnetic hard and soft phases at nanoscale so dimensionless parameters, and H, that completely charac- terize the hysteresis in a ferromagnetic polycrystal when the that they can be coupled through the intergranular exchange grain size is much larger than the exchange length so that the interaction, leading to dramatically enhanced remanence and exchange coupling can be ignored. The competition between the energy product. This again highlights the importance of inter- anisotropy energy and the intergranular magnetostatic energy granular magnetic interactions, and calls for new models that is measured by , while the competition between the anisotropy can take those interactions into account. While micromagnetic energy and Zeeman’s energy is measured by H. The hysteresis loop, magnetostatic energy density, and anisotropy energy density simulations are able to explain the remanence enhancement in calculated by using this theory agrees well with micromagnetic exchange-spring magnets [4], they are often computationally simulations. The calculations also reveal that the subnucleation extensive and time-consuming. There are also earlier efforts to field switching due to the magnetic field fluctuation is important modify the Stoner–Wohlfarth model by Atherton and Beattie when the magnet is not very hard, and that has been accounted using a mean field correction [5], where a magnetic field pro- for by a probability-based switching model. -
Magnetism Some Basics: a Magnet Is Associated with Magnetic Lines of Force, and a North Pole and a South Pole
Materials 100A, Class 15, Magnetic Properties I Ram Seshadri MRL 2031, x6129 [email protected]; http://www.mrl.ucsb.edu/∼seshadri/teach.html Magnetism Some basics: A magnet is associated with magnetic lines of force, and a north pole and a south pole. The lines of force come out of the north pole (the source) and are pulled in to the south pole (the sink). A current in a ring or coil also produces magnetic lines of force. N S The magnetic dipole (a north-south pair) is usually represented by an arrow. Magnetic fields act on these dipoles and tend to align them. The magnetic field strength H generated by N closely spaced turns in a coil of wire carrying a current I, for a coil length of l is given by: NI H = l The units of H are amp`eres per meter (Am−1) in SI units or oersted (Oe) in CGS. 1 Am−1 = 4π × 10−3 Oe. If a coil (or solenoid) encloses a vacuum, then the magnetic flux density B generated by a field strength H from the solenoid is given by B = µ0H −7 where µ0 is the vacuum permeability. In SI units, µ0 = 4π × 10 H/m. If the solenoid encloses a medium of permeability µ (instead of the vacuum), then the magnetic flux density is given by: B = µH and µ = µrµ0 µr is the relative permeability. Materials respond to a magnetic field by developing a magnetization M which is the number of magnetic dipoles per unit volume. The magnetization is obtained from: B = µ0H + µ0M The second term, µ0M is reflective of how certain materials can actually concentrate or repel the magnetic field lines. -
Experimental Search for High Curie Temperature Piezoelectric Ceramics with Combinatorial Approaches Wei Hu Iowa State University
Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2011 Experimental search for high Curie temperature piezoelectric ceramics with combinatorial approaches Wei Hu Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Part of the Materials Science and Engineering Commons Recommended Citation Hu, Wei, "Experimental search for high Curie temperature piezoelectric ceramics with combinatorial approaches" (2011). Graduate Theses and Dissertations. 10246. https://lib.dr.iastate.edu/etd/10246 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Experimental search for high Curie temperature piezoelectric ceramics with combinatorial approaches By Wei Hu A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Major: Materials Science and Engineering Program of Study Committee: Xiaoli Tan, Co-major Professor Krishna Rajan, Co-major Professor Mufit Akinc, Hui Hu, Scott Beckman Iowa State University Ames, Iowa 2011 Copyright © Wei Hu, 2011. All rights reserved. ii Table of Contents Abstract ................................................................................................................................... -
Screening Magnetic Two-Dimensional Atomic Crystals with Nontrivial Electronic Topology
Screening magnetic two-dimensional atomic crystals with nontrivial electronic topology Hang Liu,†,¶ Jia-Tao Sun,*,†,¶ Miao Liu,† and Sheng Meng*,†,‡,¶ † Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China ‡ Collaborative Innovation Center of Quantum Matter, Beijing 100190, People’s Republic of China ¶ University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China Corresponding Authors *E-mail: [email protected] (J.T.S.). *E-mail: [email protected] (S.M.). ABSTRACT: To date only a few two-dimensional (2D) magnetic crystals were experimentally confirmed, such as CrI3 and CrGeTe3, all with very low Curie temperatures (TC). High-throughput first-principles screening over a large set of materials yields 89 magnetic monolayers including 56 ferromagnetic (FM) and 33 antiferromagnetic compounds. Among them, 24 FM monolayers are promising candidates possessing TC higher than that of CrI3. High TC monolayers with fascinating electronic phases are identified: (i) quantum anomalous and valley Hall effects coexist in a single material RuCl3 or VCl3, leading to a valley-polarized quantum anomalous Hall state; (ii) TiBr3, Co2NiO6 and V2H3O5 are revealed to be half-metals. More importantly, a new type of fermion dubbed type-II Weyl ring is discovered in ScCl. Our work provides a database of 2D magnetic materials, which could guide experimental realization of high-temperature magnetic monolayers with exotic electronic states for future spintronics and quantum computing applications. KEYWORDS: Magnetic two-dimensional crystals, high throughput calculations, quantum anomalous Hall effect, valley Hall effect. 1 / 12 The discovery of two-dimensional (2D) materials opens a new avenue with rich physics promising for applications in a variety of subjects including optoelectronics, valleytronics, and spintronics, many of which benefit from the emergence of Dirac/Weyl fermions. -
1 the Paramagnet to Ferromagnet Phase Transition
Figure 1: A plot of the magnetisation of nickel (Ni) (in rather old units, sorry) as a function of temperature. The magnetisation of Ni goes to zero at its Curie temperature of 627K. 1 The Paramagnet to Ferromagnet Phase Transition The magnetic spins of a magnetic material, e.g., nickel, interact with each other: the energy is lower if the two spins on adjacent nickel atoms are parallel than if they are antiparallel. This lower energy tends to cause the spins to be parallel and below a temperature called the Curie temperature, Tc, most of the spins in the nickel are parallel, their magnetic moments then add up constructively and the piece of nickel has a net magnetic moment: it is a ferromagnet. Above the Curie temperature on average half the spins point in one direction and the other half in the opposite direction. Then their magnetic moments cancel, and the nickel has no net magnetic moment. It is then a paramagnet. Thus at Tc the nickel goes from having no magnetic moment to having a magnetic moment. See Fig. 1. This is a sudden qualitative change and when this happens we say that a phase transition has occurred. Here the phase transition occurs when the magnetic moment goes from zero to non-zero. It is from the paramagnetic phase to the ferromagnetic phase. Another example of a phase transition is when water freezes to ice, here we go from a liquid to a crystal with a crystal lattice. The lattice appears suddenly. Almost all phase transitions are like the paramagnet-to-ferromagnet phase transition and are driven by interactions. -
Magnetic Properties of Some Intra-Rare Earth Alloys Paul Edward Roughan Iowa State University
Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1962 Magnetic properties of some intra-rare earth alloys Paul Edward Roughan Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Physical Chemistry Commons Recommended Citation Roughan, Paul Edward, "Magnetic properties of some intra-rare earth alloys " (1962). Retrospective Theses and Dissertations. 2317. https://lib.dr.iastate.edu/rtd/2317 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. This dissertation has been 63—2995 microfilmed exactly as received ROUGHAN, Paul Edward, 1934- MAGNETIC PROPERTIES OF SOME INTRA- RARE EARTH ALLOYS. Iowa State University of Science and Technology Ph.D., 1962 Chemistry, physical University Microfilms, Inc., Ann Arbor, Michigan MAGNETIC PROPERTIES OF SOME INTRA-RARE EARTH ALLOYS by Paul Edward Roughan A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY Major Subject: Physical Chemistry Approved: Signature was redacted for privacy. In Charge of Major Work Signature was redacted for privacy. Head of Major Departm } Signature was redacted for privacy. Iowa State University Of Science and Technology Ames, Iowa 1962 ii TABLE OF CONTENTS Page I. INTRODUCTION 1 II. LITERATURE SURVEY 14 A. Magnetic Properties of Rare Earth Ions— Theory and Experiment 14 B. -
Practical Aspects of Modern and Future Permanent Magnets
University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Ralph Skomski Publications Research Papers in Physics and Astronomy 2014 Practical Aspects of Modern and Future Permanent Magnets R.W. McCallum Ames Laboratory, Iowa State University, Ames, Iowa L. H. Lewis Northeastern University Ralph Skomski University of Nebraska-Lincoln, [email protected] M. J. Kramer US Department of Energy, Iowa State University I. E. Anderson US Department of Energy, Iowa State University Follow this and additional works at: https://digitalcommons.unl.edu/physicsskomski Part of the Engineering Physics Commons, and the Metallurgy Commons McCallum, R.W.; Lewis, L. H.; Skomski, Ralph; Kramer, M. J.; and Anderson, I. E., "Practical Aspects of Modern and Future Permanent Magnets" (2014). Ralph Skomski Publications. 98. https://digitalcommons.unl.edu/physicsskomski/98 This Article is brought to you for free and open access by the Research Papers in Physics and Astronomy at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Ralph Skomski Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. MR44CH17-McCallum ARI 9 June 2014 14:8 Practical Aspects of Modern and Future Permanent Magnets R.W. McCallum,1,2 L.H. Lewis,3 R. Skomski,4 M.J. Kramer,1,2 and I.E. Anderson1,2 1The Ames Laboratory, US Department of Energy, Iowa State University, Ames, Iowa 50011; email: [email protected], [email protected], [email protected] 2Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011 3Department of Chemical Engineering, Northeastern University, Boston, Massachusetts 02115; email: [email protected] 4Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588; email: [email protected] Annu. -
Tailored Magnetic Properties of Exchange-Spring and Ultra Hard Nanomagnets
Max-Planck-Institute für Intelligente Systeme Stuttgart Tailored Magnetic Properties of Exchange-Spring and Ultra Hard Nanomagnets Kwanghyo Son Dissertation An der Universität Stuttgart 2017 Tailored Magnetic Properties of Exchange-Spring and Ultra Hard Nanomagnets Von der Fakultät Mathematik und Physik der Universität Stuttgart zur Erlangung der Würde eines Doktors der Naturwissenschaften (Dr. rer. nat.) genehmigte Abhandlung Vorgelegt von Kwanghyo Son aus Seoul, SüdKorea Hauptberichter: Prof. Dr. Gisela Schütz Mitberichter: Prof. Dr. Sebastian Loth Tag der mündlichen Prüfung: 04. Oktober 2017 Max‐Planck‐Institut für Intelligente Systeme, Stuttgart 2017 II III Contents Contents ..................................................................................................................................... 1 Chapter 1 ................................................................................................................................... 1 General Introduction ......................................................................................................... 1 Structure of the thesis ....................................................................................................... 3 Chapter 2 ................................................................................................................................... 5 Basic of Magnetism .......................................................................................................... 5 2.1 The Origin of Magnetism ....................................................................................... -
UNIVERSITY of CALIFORNIA, SAN DIEGO Development Of
UNIVERSITY OF CALIFORNIA, SAN DIEGO Development of Thermoelectric and Permanent Magnet Nanoparticles for Clean Energy Applications A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Materials Science and Engineering by Phi-Khanh Nguyen Committee in Charge: Professor Ami Berkowitz, Co-Chair Professor Sungho Jin, Co-Chair Professor Prabhakar Bandaru Professor Renkun Chen Professor Eric Fullerton 2015 © Phi-Khanh Nguyen, 2015 All rights reserved. SIGNATURE PAGE The dissertation of Phi-Khanh Nguyen is approved, and it is acceptable in quality and form for publication on microfilm and electronically: Co-Chair Co-Chair University of California, San Diego 2015 iii DEDICATION Dedicated to my mother and father iv EPIGRAPH “Materials science is just common sense.” - Ami E. Berkowitz v TABLE OF CONTENTS SIGNATURE PAGE ......................................................................................................... iii DEDICATION ................................................................................................................... iv EPIGRAPH ......................................................................................................................... v TABLE OF CONTENTS ................................................................................................... vi LIST OF ABBREVIATIONS ............................................................................................ ix LIST OF FIGURES ........................................................................................................... -
Exchange-Spring Behavior in Bimagnetic Cofe2o4/Cofe2
Exchange-spring behavior in bimagnetic CoFe 2O4/CoFe 2 nanocomposite Leite, G. C. P.1, Chagas, E. F. 1, Pereira, R. 1, Prado, R. J. 1, Terezo, A. J. 2 , Alzamora, M. 3, and Baggio-Saitovitch, E. 3 1Instituto de Física , Universidade Federal de Mato Grosso, 78060-900, Cuiabá- MT, Brazil 2Departamento de Química, Universidade Federal do Mato Grosso, 78060-900, Cuiabá-MT, Brazil 3Centro Brasileiro de Pesquisas Físicas, Rua Xavier Sigaud 150 Urca. Rio de Janeiro, Brazil. Phone number: 55 65 3615 8747 Fax: 55 65 3615 8730 Email address: [email protected] Abstract In this work we report a study of the magnetic behavior of ferrimagnetic oxide CoFe 2O4 and ferrimagnetic oxide/ferromagnetic metal CoFe 2O4/CoFe 2 nanocomposites. The latter compound is a good system to study hard ferrimagnet/soft ferromagnet exchange coupling. Two steps were used to synthesize the bimagnetic CoFe 2O4/CoFe 2 nanocomposites: (i) first preparation of CoFe 2O4 nanoparticles using the a simple hydrothermal method and (ii) second reduction reaction of cobalt ferrite nanoparticles using activated charcoal in inert atmosphere and high temperature. The phase structures, particle sizes, morphology, and magnetic properties of CoFe 2O4 nanoparticles have been investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) with applied field up to 3.0 kOe at room temperature and 50K. The mean diameter of CoFe 2O4 particles is about 16 nm. Mossbauer spectra reveal two sites for Fe3+. One site is related to Fe in an octahedral coordination and the other one to the Fe3+ in a tetrahedral coordination, as expected for a spinel crystal structure of CoFe 2O4.