DOCSLIB.ORG

Can Diamagnetic Currents Drive a Charge Density Wave Into Rotation?

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Can Diamagnetic Currents Drive a Charge Density Wave Into Rotation? Home Search Collections Journals About Contact us My IOPscience Time crystals: Can diamagnetic currents drive a charge density wave into rotation? This content has been downloaded from IOPscience. Please scroll down to see the full text. 2013 EPL 103 57008 (http://iopscience.iop.org/0295-5075/103/5/57008) View the table of contents for this issue, or go to the journal homepage for more Download details: IP Address: 86.137.177.48 This content was downloaded on 12/07/2017 at 20:58 Please note that terms and conditions apply. You may also be interested in: Stirring a Bose–Einstein condensate Bogdan Damski, Krzysztof Sacha and Jakub Zakrzewski Vacancy distribution in a rotating solid 4He D. I. Pushkarov One-dimensional description of a Bose–Einstein condensate in a rotating closed-loop waveguide S Schwartz, M Cozzini, C Menotti et al. Energy and momentum of electromagnetic pulses John Lekner Influence of the Earth's Rotation on Measurement of Newton's Constant by using the Angular Acceleration Method Luo Jie, Shao Cheng-Gang, Wang Dian-Hong et al. The Sagnac effect: interference in a rotating frame of reference Eyal Schwartz and Nizan Meitav A full-f calculation of spontaneous toroidal rotation in H-mode plasmas Qiong-Lin Ni, Xiao-Gang Wang, Cheng Zhang et al. Vortex dynamics and mutual friction in superconductors and Fermi superfluids N B Kopnin September 2013 EPL, 103 (2013) 57008 www.epljournal.org doi: 10.1209/0295-5075/103/57008 Time crystals: Can diamagnetic currents drive a charge density wave into rotation? Philippe Nozieres` Institut Laue Langevin - BP 156, F-38042 Grenoble Cedex 9, France, EU received 18 July 2013; accepted in final form 26 August 2013 published online 23 September 2013 PACS 75.20.-g – Diamagnetism, paramagnetism, and superparamagnetism PACS 72.15.Nj – Collective modes (e.g., in one-dimensional conductors) Abstract – It has been recently argued that an inhomogeneous system could rotate spontaneously in its ground state —hence a “time crystal” which is periodic in time. In this letter we present a very simple example: a superfluid ring threaded by a magnetic field which develops a charge density wave (CDW). A simple calculation shows that diamagnetic currents cannot drive rotation of the CDW, with a clear picture of the cancellation mechanism. editor’s choice Copyright c EPLA, 2013 In a recent letter [1] Frank Wilczek introduced a revo- ν = 0, with a diamagnetic current J = −n0qA/mc.As- lutionary concept, “time crystals” which in their ground sume now that the ring presents a spontaneous charge den- state would be time dependent. A simple example is a ring sity wave with a density modulation n1. We do not need threaded by a magnetic field that breaks time-reversal in- a periodic n1, we only request a modulation, n1dx =0. variance. If a charge density wave (CDW) appears, will The current equation becomes diamagnetic currents put it in rotation? Such a challeng- n0 + n1 qA ing proposal raised a vivid controversy [2], especially with J = grad S − . my colleague Patrick Bruno who recently provided a gen- m c eral proof that it is impossible [3]. In order to clarify the underlying physics, I study here a very simple model in J is conserved and grad S cannot vanish. We must solve which elementary calculations can be done explicitly from the equation beginning to end. qA mJ Consider a circular ring with radius R, perimeter L = S grad = c + n n 2πR, threaded by a magnetic flux Φ. The vector poten- 0 + 1 tial along the ring is A =Φ/L.AsamodeltakeaBose with the two conditions grad Sdx =0and n1dx =0 condensate of charge q particles (for Cooper pairs q =2e) which will fix the modulation grad S and the unknown with a density n0 = N0/L. The superfluid phase is S,the current J. Integrating that equation over the ring we find current density on the ring and the energy are 2 n0 qA N0 qA qA 1 J = grad S − ,E0 = grad S − . + mJ =0. m c 2m c c n S πν The circulation of grad is quantized, equal to 2 ,where Note that regions of small n severely reduce the current J, ν p is an integer. The linear momentum per particle is = a feature pointed out long ago by Tony Leggett [4]. Here grad S, without the gauge term. The angular momentum n1 is small and in lowest order we find per particle is πν 2 2 n0qA n1 Lz = R grad S = R = ν. J − − . πR = 1 2 2 mc n0 We recover the usual quantization of angular momentum. Consider first a weak magnetic field whose flux is smaller The charge density wave reduces the diamagnetic current 2 than half a quantum: the ground state corresponds to by an amount of order n1. The ground-state energy may 57008-p1 Philippe Nozi`eres be written as unfolds as before. The energy in the laboratory frame may be written as qA 1 2 E0 = J grad S − = n n qA 2 c E 0 + 1 S − 0 = m grad c 2 2 2 2 qAJ N0q A n1 − − . n0 + n1 c = mc2 1 n2 2 2 0 = m 2 qA qA × S − S − m2 2R2 Note that the charge density wave reduces the energy, a grad c grad c + Ω feature that should eventually be added to the usual Lan- qA n 1 2 2 dau picture for the appearance of 1, = J grad S − + n0mΩ R , 2 c α 2 4 2 ECDW = −αn1 + βn1 −→ n1 = . wherewehavesetA = A − mcΩR/q. The constant 2β current J is Diamagnetism enhances the charge density instability. n qA n2 J − 0 − 1 . Finally, the angular momentum Lz, zero for a diamag- = 1 2 mc n0 netic current in a perfect ring, does not vanish any more when the density wave appears: We find the energy 2 2 N0 q A A n Lz = (n0 + n1) R grad S = E − 1 m2 2R2 . 0 = m c2 1 n2 + Ω 2 0 2 qA qA n1 R (n0 + n1) + mJ = N0R 2 . 2 c c n0 The correction due to rotation is of order Ω .Thereis no linear term that could generate spontaneous rotation. Hence a crucial question: could such an angular momen- Note that this second-order term vanishes if n1 =0:ro- tum induce a spontaneous rotation of the charge density tating something which does not exist cannot cost any wave? Standard wisdom says that rotating the frame at energy! In contrast, rotating the density wave costs an angular velocity Ω adds a term LzΩ to the energy: if true, energy, rotation of the charge density wave is unavoidable since mN n2 all other terms in the energy are quadratic in Ω. A wise 0 2 2 1 E1 = Ω R 2 . pedestrian approach is to stay in the laboratory frame 2 n0 when calculating energy, noting, however, that in that frame the current is no longer conserved. It is conserved The conclusion of this naive model is clear: a charge den- in the rotating frame of the charge density wave: we start sity wave is not driven to rotation by a diamagnetic cur- ν from that statement and we bring everything back to the rent in the ground state =0. k ν/ πR laboratory frame. Generalization to an excited state = 2 is straightforward. We still have Let J be the constant current in the rotating frame. The previous calculation relates it to a vector potential A qA mJ grad S = + unknown as of now, c n0 + n1 n0 + n1 qA whose circulation is J S − ⇒ = m grad c = ν qA mJ n2 1 qA mJ = + 1+ 2 . grad S = + . R c n0 n0 c n0 + n1 The constant current J and the energy become The current J in the laboratory frame is n n2 ν qA qA J 0 − 1 − ,E 1 J S− . n0 + n1 qA = 1 2 = grad J J n n R S − . m n0 R c 2 c = +( 0 + 1)Ω = m grad c Since J is constant only the circulation of grad S matters, It follows that A = A + mcΩR/q: J is related to A hence exactly as J was to A before. Rotating the charge density N ν qA 2 n2 wave is tantamount to replacing the vector potential A by E 0 − − 1 . = 1 2 A in the rotating frame. From there on the calculation 2m R c n0 57008-p2 Time crystals: Can diamagnetic currents drive a charge density wave into rotation? The only difference is the replacement of eA/c by (eA/c− ∗∗∗ ν/R). From there on the calculation is unchanged. I wish to thank my colleagues Patrick Bruno and Our final conclusion is clear, but limited: a charge den- Andres Cano who introduced me to the challenge of time sity wave is not driven to rotation in a quantum coherent crystals. Numerous discussions with them were crucial in state, for instance by a diamagnetic current induced by a my search for simplicity. The reader is referred to the magnetic field, or by a persistent current in a coherent, paper of Patrick Bruno [3] which offers a much more phase locked, superfluid state. This is consistent with the general proof, necessarily more elaborate. His conclusions Ehrenfest theorem which states that the expectation value are fully consistent with my simple picture. of the time derivative of any observable A is identically zero in any eigenstate |ψn of the Hamiltonian: Additional remark: Nowadays basic concepts and sim- ple proofs may hardly find their way on highly reputed dA physics journals.
Load more

Recommended publications
  • Optical Properties of Nanostructured Random Media
    Vladimir M. Shalaev (Ed.) Optical Properties of Nanostructured Random Media With 185 Figures Springer Contents Nanocomposite Materials for Nonlinear Optics Based on Local Field Effects John E. Sipe and Robert W. Boyd 1 1. Tntroduction 1 2. Linear Optical Properties 3 3. Nonlinear Optical Properties 8 4. Recent Advances 14 References 17 Response of Composite Media Made of Weakly Nonlinear Constituents David J. Bergman and David G. Stroud 19 1. Introduction 19 2. Perturbation Thcory 20 3. Limiting Gases and Exactly Solvable Microstructures 24 3.1. Parallel Cylmders and Parallel Slabs 24 3.2. Dilute Regime and Clausius- Mossotti Approximation 25 4. Self-Consistent Effective Medium Approximation and Its Breakdown . 27 5. Quasi-static Resonances: Enhancement of Nonlinearity and Intrinsic Optical Bistability 31 5.1. Solvable Microstructures 32 5.2. The Principle of "Zero Virtual Work" and Its Application 35 5.3. Harmonie Generation and Induccd Nonlinearity 37 References 38 Third-Order Nonlinear Properties of Au Clusters Containing Dielectric Thin Films Hongru Ma, Ping Sheng, and George K. L. Wong 41 1. Introduction 41 2. Experimental 42 2.1. Preparation and Charaeterization of Samples 42 2.2. Nonlinear Optical Measurements 45 X Contents 3. Theoretical 49 3.1. General Theory 49 3.2. Application of the Theory to Four Effective Medium Theories ... 53 3.3. Illustrations and Comparison of Theory with Experiments 57 Refcrences 60 Linear and Nonlinear Optical Properties of Quasi-Periodic One-Dimensional Structures Concita Sibilia, Mario Bcrtolotti, Marco Centini, Giuseppe D'Aguanno, Michael Scalora, Mark J. Bloemer, and Charles M. Bowden 63 1. Introduction 63 2. Something about Fractals 64 3.
    [Show full text]
  • Coexistence of Superparamagnetism and Ferromagnetism in Co-Doped
    Available online at www.sciencedirect.com ScienceDirect Scripta Materialia 69 (2013) 694–697 www.elsevier.com/locate/scriptamat Coexistence of superparamagnetism and ferromagnetism in Co-doped ZnO nanocrystalline films Qiang Li,a Yuyin Wang,b Lele Fan,b Jiandang Liu,a Wei Konga and Bangjiao Yea,⇑ aState Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei 230026, People’s Republic of China bNational Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, People’s Republic of China Received 8 April 2013; revised 5 August 2013; accepted 6 August 2013 Available online 13 August 2013 Pure ZnO and Zn0.95Co0.05O films were deposited on sapphire substrates by pulsed-laser deposition. We confirm that the magnetic behavior is intrinsic property of Co-doped ZnO nanocrystalline films. Oxygen vacancies play an important mediation role in Co–Co ferromagnetic coupling. The thermal irreversibility of field-cooling and zero field-cooling magnetizations reveals the presence of superparamagnetic behavior in our films, while no evidence of metallic Co clusters was detected. The origin of the observed superparamagnetism is discussed. Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Dilute magnetic semiconductors; Superparamagnetism; Ferromagnetism; Co-doped ZnO Dilute magnetic semiconductors (DMSs) have magnetic properties in this system. In this work, the cor- attracted increasing attention in the past decade due to relation between the structural features and magnetic their promising technological applications in the field properties of Co-doped ZnO films was clearly of spintronic devices [1]. Transition metal (TM)-doped demonstrated. ZnO is one of the most attractive DMS candidates The Zn0.95Co0.05O films were deposited on sapphire because of its outstanding properties, including room- (0001) substrates by pulsed-laser deposition using a temperature ferromagnetism.
    [Show full text]
  • Label-Free Detection and Manipulation of Single Biological Nanoparticles
    Article type: Advanced Review Article title: Label-free detection and manipulation of single biological nanoparticles Authors: Full name and affiliation; email address if corresponding author; any conflicts of interest First author Michael C. DeSantis Department of Pharmaceutical Sciences, College of Pharmacy, University of Michigan, Ann Arbor, MI 48109, USA Second author Wei Cheng Department of Pharmaceutical Sciences, College of Pharmacy, University of Michigan, Ann Arbor, MI 48109, USA Department of Biophysics, University of Michigan, Ann Arbor, MI 48109, USA [email protected] Third author [Type information here] Abstract In the past several years, there have been significant advances in the field of nanoparticle detection for various biological applications. Of considerable interest are synthetic nanoparticles being designed as potential drug delivery systems as well as naturally occurring or biological nanoparticles, including viruses and extracellular vesicles. Many infectious diseases and several human cancers are attributed to individual virions. Because these particles likely display different degrees of heterogeneity under normal physiological conditions, characterization of these natural nanoparticles with single-particle sensitivity is necessary for elucidating information on their basic structure and function as well as revealing novel targets for therapeutic intervention. Additionally, biodefense and point-of-care clinical testing demand ultrasensitive detection of viral pathogens particularly with high specificity. Consequently, the ability to perform label-free virus sensing has motivated the This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/wnan.1392 This article is protected by copyright.
    [Show full text]
  • Modulation of Magneto-Optical Properties of Metallic Nanostructures by External Stimuli
    Modulation of Magneto-Optical Properties of Metallic Nanostructures by External Stimuli by Abid Siddique B.Sc. in Electrical Engineering, May 2007, UET Peshawar, Pakistan M.S. in Electrical Engineering, May 2010, The George Washington University A Dissertation submitted to The Faculty of The School of Engineering and Applied Science of The George Washington University in partial fulfillment of the requirements for the degree of Doctor of Philosophy January 19, 2018 Dissertation directed by Edward Della Torre Professor of Engineering and Applied Science Lawrence H. Bennett Research Professor of Engineering and Applied Science The School of Engineering and Applied Science of The George Washington University certifies that Abid Siddique has passed the Final Examination for the degree of Doctor of Philosophy as of December 19th, 2017. This is the final and approved form of the dissertation. Modulation of Magneto-Optical Properties of Metallic Nanostructures by External Stimuli Abid Siddique Dissertation Research Committee: Edward Della Torre, IEEE Life Fellow and Professor of Engineering and Applied Science, Dissertation Co-Director Lawrence H. Bennett, Fellow of the American Physical Society and Research Professor of Engineering and Applied Science, Dissertation Co-Director Robert J. Harrington, Fellow of IEEE and Professor of Engineering and Applied Science, Committee Member Shahrokh Ahmadi, Professor of Engineering and Applied Science, Committee Member Dr. Chidubem A. Nwokoye, Electrical Engineer, Naval Surface Warfare Center, Carderock Division, Committee Member ii © Copyright 2018 by Abid Siddique All rights reserved iii Dedication I dedicate my dissertation to my beloved parents, whose love, prayers, sacrifices, and never-ending inspiration for hard work remained a source of guidance throughout my life.
    [Show full text]
  • Introduction to AC Susceptibility
    QuantumDesign Introduction to: AC Susceptibility AC Magnetic Measurements Dinesh Martien Introduction AC magnetic measurements, in which an AC field is applied to a sample and the resulting AC moment is measured, are an important tool for characterizing many materials. Because the induced sample moment is time-dependent, AC measurements yield information about magnetization dynamics which are not AC Magnetometry obtained in DC measurements, where the sample moment is constant during the measurement time. This application note In AC magnetic measurements, a small AC drive magnetic field will briefly describe how AC magnetic measurements are is superimposed on the DC field, causing a time-dependent performed, discuss the meaning of the data that come out of moment in the sample. The field of the time-dependent an AC measurement, and show some measurement examples. moment induces a current in the pickup coils, allowing meas- urement without sample motion. The detection circuitry is configured to detect only in a narrow frequency band, normally DC Magnetometry at the fundamental frequency (that of the AC drive field). DC magnetic measurements determine the equilibrium value In order to understand what is measured in AC magnetometry, of the magnetization in a sample. The sample is magnetized first consider very low frequencies, where the measurement is by a constant magnetic field and the magnetic moment of the most similar to DC magnetometry. In this case, the magnetic sample is measured, producing a DC magnetization curve moment of the sample follows the M(H) curve that would be M(H) . The moment is measured by force, torque or induc- measured in a DC experiment.
    [Show full text]
  • Low-Field-Enhanced Unusual Hysteresis Produced By
    PHYSICAL REVIEW B 94, 184427 (2016) Low-field-enhanced unusual hysteresis produced by metamagnetism of the MnP clusters in the insulating CdGeP2 matrix under pressure T. R. Arslanov,1,* R. K. Arslanov,1 L. Kilanski,2 T. Chatterji,3 I. V. Fedorchenko,4,5 R. M. Emirov,6 and A. I. Ril5 1Amirkhanov Institute of Physics, Daghestan Scientific Center, Russian Academy of Sciences (RAS), 367003 Makhachkala, Russia 2Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland 3Institute Laue-Langevin, Boˆıte Postale 156, 38042 Grenoble Cedex 9, France 4Kurnakov Institute of General and Inorganic Chemistry, RAS, 119991 Moscow, Russia 5National University of Science and Technology MISiS, 119049, Moscow, Russia 6Daghestan State University, Faculty of Physics, 367025 Makhachkala, Russia (Received 11 April 2016; revised manuscript received 28 October 2016; published 22 November 2016) Hydrostatic pressure studies of the isothermal magnetization and volume changes up to 7 GPa of magnetic composite containing MnP clusters in an insulating CdGeP2 matrix are presented. Instead of alleged superparamagnetic behavior, a pressure-induced magnetization process was found at zero magnetic field, showing gradual enhancement in a low-field regime up to H 5 kOe. The simultaneous application of pressure and magnetic field reconfigures the MnP clusters with antiferromagnetic alignment, followed by onset of a field-induced metamagnetic transition. An unusual hysteresis in magnetization after pressure cycling is observed, which is also enhanced by application of the magnetic field, and indicates reversible metamagnetism of MnP clusters. We relate these effects to the major contribution of structural changes in the composite, where limited volume reduction by 1.8% is observed at P ∼ 5.2 GPa.
    [Show full text]
  • Superparamagnetism and Magnetic Properties of Ni Nanoparticles Embedded in Sio2
    PHYSICAL REVIEW B 66, 104406 ͑2002͒ Superparamagnetism and magnetic properties of Ni nanoparticles embedded in SiO2 F. C. Fonseca, G. F. Goya, and R. F. Jardim* Instituto de Fı´sica, Universidade de Sa˜o Paulo, CP 66318, 05315-970, Sa˜o Paulo, SP, Brazil R. Muccillo Centro Multidisciplinar de Desenvolvimento de Materiais Ceraˆmicos CMDMC, CCTM-Instituto de Pesquisas Energe´ticas e Nucleares, CP 11049, 05422-970, Sa˜o Paulo, SP, Brazil N. L. V. Carren˜o, E. Longo, and E. R. Leite Centro Multidisciplinar de Desenvolvimento de Materiais Ceraˆmicos CMDMC, Departamento de Quı´mica, Universidade Federal de Sa˜o Carlos, CP 676, 13560-905, Sa˜o Carlos, SP, Brazil ͑Received 4 March 2002; published 6 September 2002͒ We have performed a detailed characterization of the magnetic properties of Ni nanoparticles embedded in a SiO2 amorphous matrix. A modified sol-gel method was employed which resulted in Ni particles with ϳ Ϸ average radius 3 nm, as inferred by TEM analysis. Above the blocking temperature TB 20 K for the most diluted sample, magnetization data show the expected scaling of the M/M S vs H/T curves for superparamag- netic particles. The hysteresis loops were found to be symmetric about zero field axis with no shift via Ͻ exchange bias, suggesting that Ni particles are free from an oxide layer. For T TB the magnetic behavior of these Ni nanoparticles is in excellent agreement with the predictions of randomly oriented and noninteracting magnetic particles, as suggested by the temperature dependence of the coercivity field that obeys the relation ϭ Ϫ 1/2 ϳ HC(T) HC0͓1 (T/TB) ͔ below TB with HC0 780 Oe.
    [Show full text]
  • Magnetic Susceptibility of Nio Nanoparticles
    Magnetic Susceptibility of NiO Nanoparticles S. D. Tiwari and K. P. Rajeev Department of Physics, Indian Institute of Technology, Kanpur 208016, Uttar Pradesh, India Nickel oxide nanoparticles of different sizes are prepared and characterized by x-ray diffraction and transmission electron microscopy. A.C. susceptibility measurements as a function of temperature are carried out for various particle sizes and frequencies. We find that the behavior of the system is spin glass like. PACS number(s): 61.46.+w, 75.20.-g, 75.50.Ee, 75.50.Tt, 75.50.Lk, 75.75.+a Keywords: nanoparticles; magnetic property; susceptibility; superparamagnetism; spin glass. During the last few decades magnetic nanoparticles have been attracting the attention of scientists both from the view point of fundamental understanding as well as applications1. Magnetic nanoparticles have been a subject of interest since the days of Néel2 and Brown3 who developed the theory of magnetization relaxation for noninteracting single domain particles. Effects of interparticle interactions on magnetic properties of several nanoparticle systems have been reported by several authors4. In 1961 Néel suggested that small particles of an antiferromagnetic material should exhibit 1 magnetic properties such as superparamagnetism and weak ferromagnetism5. Antiferromagnetic nanoparticles show more interesting behavior compared to ferro and ferrimagnetic nanoparticles. One such interesting behavior is that the magnetic moment of tiny antiferromagnetic particles increases with increasing temperature6 , 7 which is quite unlike what is seen in ferro or ferrimagnetic particles. Real magnetic nanoparticles have disordered arrangement, distribution in size and random orientation of easy axes of magnetization, making their behavior very complex and enigmatic. Bulk NiO has rhombohedral structure and is antiferromagnetic below 523 K whereas it has cubic structure and is paramagnetic above that temperature8.
    [Show full text]
  • Monitoring the Dispersion and Agglomeration of Silver
    Monitoring the dispersion and agglomeration of silver nanoparticles in polymer thin films using Localized Surface Plasmons and Ferrell Plasmons Rafael Hensel, Murilo Moreira, Antonio Riul, Osvaldo Oliveira, Varlei Rodrigues, Matthias Hillenkamp To cite this version: Rafael Hensel, Murilo Moreira, Antonio Riul, Osvaldo Oliveira, Varlei Rodrigues, et al.. Monitoring the dispersion and agglomeration of silver nanoparticles in polymer thin films using Localized Surface Plasmons and Ferrell Plasmons. Applied Physics Letters, American Institute of Physics, 2020, 116 (10), pp.103105. 10.1063/1.5140247. hal-02497318 HAL Id: hal-02497318 https://hal.archives-ouvertes.fr/hal-02497318 Submitted on 3 Mar 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Monitoring the dispersion and agglomeration of silver nanoparticles in polymer thin films using Localized Surface Plasmons and Ferrell Plasmons Rafael C. Hensel1, Murilo Moreira1, Antonio Riul Jr1, Osvaldo N. Oliveira Jr2, Varlei Rodrigues1, Matthias Hillenkamp1,3 * 1 Instituto de Física Gleb Wataghin, UNICAMP, CP 6165, 13083-970 Campinas, SP, Brazil 2 São Carlos Institute of Physics (IFSC), University of São Paulo (USP), P.O. Box 369, 13566-590 São Carlos, SP, Brazil 3 Institute of Light and Matter, Univ.
    [Show full text]
  • Nanoparticle Synthesis for Magnetic Hyperthermia
    Declaration Nanoparticle Synthesis For Magnetic Hyperthermia This thesis is submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy (Chemistry) Luanne Alice Thomas Supervised by Professor I. P. Parkin University College London Christopher Ingold Laboratories, 20 Gordon Street, WC1H 0AJ 2010 i Declaration I, Luanne A. Thomas, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. ii Abstract Abstract This work reports on an investigation into the synthesis, control, and stabilisation of iron oxide nanoparticles for biomedical applications using magnetic hyperthermia. A new understanding of the factors effecting nanoparticle growth in a coprecipitation methodology has been determined. This thesis challenges the highly cited Ostwald Ripening as the primary mechanism for nanoparticulate growth, and instead argues that in certain conditions, such as increasing reaction temperature, a coalescence mechanism could be favoured by the system. Whereas in a system with a slower rate of addition of the reducing agent, Ostwald ripening is the favoured mechanism. The iron oxide nanoparticles made in the study were stabilised and functionalised for the purpose of stability in physiological environments using either carboxylic acid or phosphonate functionalised ligands. It was shown that phosphonate ligands form a stronger attachment to the nanoparticle surface and promote increased stability in aqueous solutions, however, this affected the magnetic properties of the particles and made them less efficient heaters when exposed to an alternating magnetic fields. Tiopronin coated iron oxide nanoparticles were a far superior heater, being over four times more effective than the best commercially available product.
    [Show full text]
  • Superparamagnetism and Magneto-Caloric Effect (Mce) in Functional Magnetic Nanostructures
    398Rev.Adv.Mater.Sci. 10 (2005) 398-402 Srikanth Hariharan and James Gass SUPERPARAMAGNETISM AND MAGNETO-CALORIC EFFECT (MCE) IN FUNCTIONAL MAGNETIC NANOSTRUCTURES Srikanth Hariharan and James Gass Materials Physics Laboratory, Department of Physics, University of South Florida, Tampa, FL 33620, USA Received: May 25, 2005 Abstract. Magnetic nanoparticles exhibit superparamagnetic and ferromagnetic behaviors con- trolled by the particle size and interactions. While monodisperse nanoparticles are of interest from fundamental science perspective, functional nanostructures involve dispersion of particles in host matrices such as polymers. We discuss synthesis and magnetism of polymer nanocomposites based on PMMA with embedded Fe O nanoparticles. An interesting applica- 3 4 tion of nanoparticle assemblies is in magneto-caloric effect (MCE) that has the potential for local cooling/heating of NEMS and MEMS devices. We have studied MCE in CoFe O nanoparticles by 2 4 measuring family of M-H curves at set temperature intervals and calculated the entropy change (∆S) for this system. 1. INTRODUCTION ogy, electromagnetic devices [2,3]. For example, the lack of magnetic hysteresis coupled with high Magnetic nanoparticles behave very differently from saturation magnetization is highly desirable in RF bulk or thin film systems. When the size of the and microwave magnetic applications as the mag- particles is reduced below the single domain limit netic losses are considerably reduced. In addition, (~15 to 20 nm for iron oxide), they exhibit the granular and disconnected nature of nanoparticle superparamagnetism at room temperature followed assemblies prevents eddy current losses too. by a spin-glass like transition at low temperature For device applications, since particles are gen- [1].
    [Show full text]
  • Superparamagnetic Nanoparticle Ensembles
    1 Superparamagnetic nanoparticle ensembles O. Petracic Institute of Experimental Physics/Condensed Matter Physics, Ruhr-University Bochum, 44780 Bochum, Germany Abstract: Magnetic single-domain nanoparticles constitute an important model system in magnetism. In particular ensembles of superparamagnetic nanoparticles can exhibit a rich variety of different behaviors depending on the inter-particle interactions. Starting from isolated single-domain ferro- or ferrimagnetic nanoparticles the magnetization behavior of both non-interacting and interacting particle-ensembles is reviewed. A particular focus is drawn onto the relaxation time of the system. In case of interacting nanoparticles the usual Néel-Brown relaxation law becomes modified. With increasing interactions modified superparamagnetism, spin glass behavior and superferromagnetism are encountered. 1. Introduction Nanomagnetism is a vivid and highly interesting topic of modern solid state magnetism and nanotechnology [1-4]. This is not only due to the ever increasing demand for miniaturization, but also due to novel phenomena and effects which appear only on the nanoscale. That is e.g. superparamagnetism, new types of magnetic domain walls and spin structures, coupling phenomena and interactions between electrical current and magnetism (magneto resistance and current-induced switching) [1-4]. In technology nanomagnetism has become a crucial commercial factor. Modern magnetic data storage builds on principles of nanomagnetism and this tendency will increase in future. Also other areas of nanomagnetism are commercially becoming more and more important, e.g. for sensors [5] or biomedical applications [6]. Many potential future applications are investigated, e.g. magneto-logic devices [7], [8], photonic systems [9, 10] or magnetic refrigeration [11, 12]. 2 In particular magnetic nanoparticles experience a still increasing attention, because they can serve as building blocks for e.g.
    [Show full text]