Demagnetizing Fields and Magnetization Reversal in Permanent Magnets
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Basic Magnetic Measurement Methods
Basic magnetic measurement methods Magnetic measurements in nanoelectronics 1. Vibrating sample magnetometry and related methods 2. Magnetooptical methods 3. Other methods Introduction Magnetization is a quantity of interest in many measurements involving spintronic materials ● Biot-Savart law (1820) (Jean-Baptiste Biot (1774-1862), Félix Savart (1791-1841)) Magnetic field (the proper name is magnetic flux density [1]*) of a current carrying piece of conductor is given by: μ 0 I dl̂ ×⃗r − − ⃗ 7 1 - vacuum permeability d B= μ 0=4 π10 Hm 4 π ∣⃗r∣3 ● The unit of the magnetic flux density, Tesla (1 T=1 Wb/m2), as a derive unit of Si must be based on some measurement (force, magnetic resonance) *the alternative name is magnetic induction Introduction Magnetization is a quantity of interest in many measurements involving spintronic materials ● Biot-Savart law (1820) (Jean-Baptiste Biot (1774-1862), Félix Savart (1791-1841)) Magnetic field (the proper name is magnetic flux density [1]*) of a current carrying piece of conductor is given by: μ 0 I dl̂ ×⃗r − − ⃗ 7 1 - vacuum permeability d B= μ 0=4 π10 Hm 4 π ∣⃗r∣3 ● The Physikalisch-Technische Bundesanstalt (German national metrology institute) maintains a unit Tesla in form of coils with coil constant k (ratio of the magnetic flux density to the coil current) determined based on NMR measurements graphics from: http://www.ptb.de/cms/fileadmin/internet/fachabteilungen/abteilung_2/2.5_halbleiterphysik_und_magnetismus/2.51/realization.pdf *the alternative name is magnetic induction Introduction It -
Coey-Slides-1.Pdf
These lectures provide an account of the basic concepts of magneostatics, atomic magnetism and crystal field theory. A short description of the magnetism of the free- electron gas is provided. The special topic of dilute magnetic oxides is treated seperately. Some useful books: • J. M. D. Coey; Magnetism and Magnetic Magnetic Materials. Cambridge University Press (in press) 600 pp [You can order it from Amazon for £ 38]. • Magnétisme I and II, Tremolet de Lachesserie (editor) Presses Universitaires de Grenoble 2000. • Theory of Ferromagnetism, A Aharoni, Oxford University Press 1996 • J. Stohr and H.C. Siegmann, Magnetism, Springer, Berlin 2006, 620 pp. • For history, see utls.fr Basic Concepts in Magnetism J. M. D. Coey School of Physics and CRANN, Trinity College Dublin Ireland. 1. Magnetostatics 2. Magnetism of multi-electron atoms 3. Crystal field 4. Magnetism of the free electron gas 5. Dilute magnetic oxides Comments and corrections please: [email protected] www.tcd.ie/Physics/Magnetism 1 Introduction 2 Magnetostatics 3 Magnetism of the electron 4 The many-electron atom 5 Ferromagnetism 6 Antiferromagnetism and other magnetic order 7 Micromagnetism 8 Nanoscale magnetism 9 Magnetic resonance Available November 2009 10 Experimental methods 11 Magnetic materials 12 Soft magnets 13 Hard magnets 14 Spin electronics and magnetic recording 15 Other topics 1. Magnetostatics 1.1 The beginnings The relation between electric current and magnetic field Discovered by Hans-Christian Øersted, 1820. ∫Bdl = µ0I Ampère’s law 1.2 The magnetic moment Ampère: A magnetic moment m is equivalent to a current loop. Provided the current flows in a plane m = IA units Am2 In general: m = (1/2)∫ r × j(r)d3r where j is the current density; I = j.A so m = 1/2∫ r × Idl = I∫ dA = m Units: Am2 1.3 Magnetization Magnetization M is the local moment density M = δm/δV - it fluctuates wildly on a sub-nanometer and a sub-nanosecond scale. -
Magnetization and Demagnetization Studies of a HTS Bulk in an Iron Core Kévin Berger, Bashar Gony, Bruno Douine, Jean Lévêque
Magnetization and Demagnetization Studies of a HTS Bulk in an Iron Core Kévin Berger, Bashar Gony, Bruno Douine, Jean Lévêque To cite this version: Kévin Berger, Bashar Gony, Bruno Douine, Jean Lévêque. Magnetization and Demagnetization Stud- ies of a HTS Bulk in an Iron Core. IEEE Transactions on Applied Superconductivity, Institute of Electrical and Electronics Engineers, 2016, 26 (4), pp.4700207. 10.1109/TASC.2016.2517628. hal- 01245678 HAL Id: hal-01245678 https://hal.archives-ouvertes.fr/hal-01245678 Submitted on 19 Dec 2015 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. 1PoBE_12 1 Magnetization and Demagnetization Studies of a HTS Bulk in an Iron Core Kévin Berger, Bashar Gony, Bruno Douine, and Jean Lévêque Abstract—High Temperature Superconductors (HTS) are large quantity, with good and homogeneous properties, they promising materials in variety of practical applications due to are still the most promising materials for the applications of their ability to act as powerful permanent magnets. Thus, in this superconductors. paper, we have studied the influence of some pulsed and There are several ways to magnetize HTS bulks; but we pulsating magnetic fields applied to a magnetized HTS bulk assume that the most convenient one is to realize a method in sample. -
Module 2C: Micromagnetics
Module 2C: Micromagnetics Debanjan Bhowmik Department of Electrical Engineering Indian Institute of Technology Delhi Abstract In this part of the second module (2C) we will show how the Stoner Wolfarth/ single domain mode of ferromagnetism often fails to match with experimental data. We will introduce domain walls in that context and explain the basic framework of micromagnetics, which can be used to model domain walls. Then we will discuss how an anisotropic exchange interaction, known as Dzyaloshinskii Moriya interaction, can lead to chirality of the domain walls. Then we will introduce another non-uniform magnetic structure known as skyrmion and discuss its stability, based on topological arguments. 1 1 Brown's paradox in ferromagnetic thin films exhibiting perpendicular magnetic anisotropy We study ferromagnetic thin films exhibiting Perpendicular Magnetic Anisotropy (PMA) to demonstrate the failure of the previously discussed Stoner Wolfarth/ single domain model to explain experimentally observed magnetic switching curves. PMA is a heavily sought after property in magnetic materials for memory and logic applications (we will talk about that in details in the next module). This makes our analysis in this section even more relevant. The ferromagnetic layer in the Ta/CoFeB/MgO stack, grown by room temperature sput- tering, exhibits perpendicular magnetic anisotropy with an anisotropy field Hk of around 2kG needed to align the magnetic moment in-plane (Fig. 1a). Thus if the ferromagnetic layer is considered as a giant macro-spin in the Stoner Wolfarth model an energy barrier equivalent to ∼2kG exists between the up (+z) and down state (-z) (Fig. 1b). Yet mea- surement shows that the magnet can be switched by a field, called the coercive field, as small as ∼50 G, which is 2 orders of magnitude smaller than the anisotropy field Hk, as observed in the Vibrating Sample Magnetometry measurement on the stack (Fig. -
Apparatus for Magnetization and Efficient Demagnetization of Soft
3274 IEEE TRANSACTIONS ON MAGNETICS, VOL. 45, NO. 9, SEPTEMBER 2009 Apparatus for Magnetization and Efficient Demagnetization of Soft Magnetic Materials Paul Oxley Physics Department, The College of the Holy Cross, Worcester, MA 01610 USA This paper describes an electrical circuit that can be used to automatically magnetize and ac-demagnetize moderately soft magnetic materials and with minor modifications could be used to demagnetize harder magnetic materials and magnetic geological samples. The circuit is straightforward to replicate, easy to use, and low in cost. Independent control of the demagnetizing current frequency, am- plitude, and duration is available. The paper describes the circuit operation in detail and shows that it can demagnetize a link-shaped specimen of 430FR stainless steel with 100% efficiency. Measurements of the demagnetization efficiency of the specimen with different ac-demagnetization frequencies are interpreted using eddy-current theory. The experimental results agree closely with the theoretical predictions. Index Terms—Demagnetization, demagnetizer, eddy currents, magnetic measurements, magnetization, residual magnetization. I. INTRODUCTION to magnetize a magnetic sample by delivering a current propor- HERE is a widespread need for a convenient and eco- tional to an input voltage provided by the user and can be used T nomical apparatus that can ac-demagnetize magnetic ma- to measure magnetic properties such as - hysteresis loops terials. It is well known that to accurately measure the mag- and magnetic permeability. netic properties of a material, it must first be in a demagnetized Our apparatus is simple, easy to use, and economical. It state. For this reason, measurements of magnetization curves uses up-to-date electronic components, unlike many previous and hysteresis loops use unmagnetized materials [1], [2] and it designs [9]–[13], which therefore tend to be rather compli- is thought that imprecise demagnetization is a leading cause for cated. -
Spin Wave Dispersion in a Magnonic Waveguide G
1 Proposal for a standard micromagnetic problem: Spin wave dispersion in a magnonic waveguide G. Venkat, D. Kumar, M. Franchin, O. Dmytriiev, M. Mruczkiewicz, H. Fangohr, A. Barman, M. Krawczyk, and A. Prabhakar Abstract—We propose a standard micromagnetic problem, of Micromagnetic Framework (OOMMF) [12], LLG [13], Micro- a nanostripe of permalloy. We study the magnetization dynamics magus [14] and Nmag [15]. We rely on the finite difference and describe methods of extracting features from simulations. method (FDM) adopted by OOMMF and the finite element Spin wave dispersion curves, relating frequency and wave vector, are obtained for wave propagation in different directions relative method (FEM) used in Nmag. The latter is more suitable for to the axis of the waveguide and the external applied field. geometries with irregular edges [16]. However, the compu- Simulation results using both finite element (Nmag) and finite tation overhead and management of resources become major difference (OOMMF) methods are compared against analytic issues in FEM simulations. To compare different numerical results, for different ranges of the wave vector. solvers, the Micromagnetic Modeling Activity Group (µMag) Index Terms—Computational micromagnetics, spin wave dis- publishes standard problems for micromagnetism [17]–[19]. persion, exchange dominated spin waves A more recent addition included the effects of spin transfer torque [20]. However, there has thus far been no standard INTRODUCTION problem that includes the calculation of the spin wave dis- There have been steady improvements in computational persion of a magnonic waveguide. We believe that specifying micromagnetics in recent years, both in techniques as well as a standard problem will promote the use of micromagnetic in the use of graphical processing units (GPUs) [1]–[4]. -
Advanced Micromagnetics and Atomistic Simulations of Magnets
Advanced micromagnetics and atomistic simulations of magnets Richard F L Evans ESM 2018 Overview • Micromagnetics • Formulation and approximations • Energetic terms and magnetostatics • Magnetisation dynamics • Atomistic spin models • Foundations and approximations • Monte Carlo methods • Spin Dynamics • Landau-Lifshitz-Bloch micromagnetics (tomorrow) Micromagnetics source: mumax Why do we need magnetic simulations? Demagnetization factors for different shapes N = 0 N = 1/3 N = 1/2 N = 1 Infinite thin film Infinitely long Sphere cylinder Infinitely long cylinder Short cylinder Why do we need magnetic simulations? Jay Shah et al, Nature Communications 9 1173 (2018) Why do we need magnetic simulations? • Most magnetic problems are not solvable analytically • Complex shapes (cube or finite geometric shapes) • Complex structures (polygranular materials, multilayers, devices) • Magnetization dynamics • Thermal effects • Metastable phases (Skyrmions) Analytical micromagnetics • An analytical branch of micromagnetics, treating magnetism on a small (micrometre) length scale • Mathematically messy but elegant • When we talk about micromagnetics, we usually mean numerical micromagnetics Numerical micromagnetics • Treat magnetisation as a continuum approximation <M> • Average over the local atomic moments to give an average moment density (magnetization) that is assumed to be continuous • Then consider a small volume of space (1 nm)3 - (10 nm)3 where the magnetization (and all atomic moments) are assumed to point along the same direction The micromagnetic -
Quantum Mechanics Magnetization This Article Is About Magnetization As It Appears in Maxwell's Equations of Classical Electrodynamics
Quantum Mechanics_magnetization This article is about magnetization as it appears in Maxwell's equations of classical electrodynamics. For a microscopic description of how magnetic materials react to a magnetic field, see magnetism. For mathematical description of fields surrounding magnets and currents, see magnetic field. In classical Electromagnetism, magnetization [1] ormagnetic polarization is the vector field that expresses the density of permanent or inducedmagnetic dipole moments in a magnetic material. The origin of the magnetic moments responsible for magnetization can be either microscopic electric currents resulting from the motion of electrons inatoms, or the spin of the electrons or the nuclei. Net magnetization results from the response of a material to an external magnetic field, together with any unbalanced magnetic dipole moments that may be inherent in the material itself; for example, inferromagnets. Magnetization is not alwayshomogeneous within a body, but rather varies between different points. Magnetization also describes how a material responds to an appliedmagnetic field as well as the way the material changes the magnetic field, and can be used to calculate the forces that result from those interactions. It can be compared to electric polarization, which is the measure of the corresponding response of a material to an Electric field in Electrostatics. Physicists and engineers define magnetization as the quantity of magnetic moment per unit volume. It is represented by a vector M. Contents 1 Definition 2 Magnetization in Maxwell's equations 2.1 Relations between B, H, and M 2.2 Magnetization current 2.3 Magnetostatics 3 Magnetization dynamics 4 Demagnetization 4.1 Applications of Demagnetization 5 See also 6 Sources Definition Magnetization can be defined according to the following equation: Here, M represents magnetization; m is the vector that defines the magnetic moment; V represents volume; and N is the number of magnetic moments in the sample. -
Modeling Shape Effects in Nano Magnetic Materials with Web Based Micromagnetics
University of New Orleans ScholarWorks@UNO University of New Orleans Theses and Dissertations Dissertations and Theses 5-21-2005 Modeling Shape Effects in Nano Magnetic Materials With Web Based Micromagnetics Zhidong Zhao University of New Orleans Follow this and additional works at: https://scholarworks.uno.edu/td Recommended Citation Zhao, Zhidong, "Modeling Shape Effects in Nano Magnetic Materials With Web Based Micromagnetics" (2005). University of New Orleans Theses and Dissertations. 157. https://scholarworks.uno.edu/td/157 This Dissertation is protected by copyright and/or related rights. It has been brought to you by ScholarWorks@UNO with permission from the rights-holder(s). You are free to use this Dissertation in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Dissertation has been accepted for inclusion in University of New Orleans Theses and Dissertations by an authorized administrator of ScholarWorks@UNO. For more information, please contact [email protected]. MODELING SHAPE EFFECTS IN NANO MAGNETIC MATERIALS WITH WEB BASED MICROMAGNETICS A Dissertation Submitted to the Graduate Faculty of the University of New Orleans in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry by Zhidong Zhao B.S., Huazhong University of Science and Technology, 1989 M.S., Beijing Normal University, 1992 May 2004 Acknowledgement I would like to express my sincere thanks to my supervisor, Professor Scott L. -
Chapter 1 Standard Problems in Micromagnetics
May 31, 2018 18:6 ws-rv961x669 Book Title porter page 1 Chapter 1 Standard Problems in Micromagnetics Donald Porter and Michael Donahue National Institute of Standards and Technology, 100 Bureau Drive, Stop 8910, Gaithersburg, MD 20899-8910, USA [email protected] Micromagnetics is a continuum model of magnetization processes at the nanome- ter scale. It is largely a computational science, and as such it faces the same issues of clarity, confidence and reproducibility as any computational effort. A curated collection of well-defined reference problems, accepted by and solved by the associated research community, can address these issues by aiding commu- nication and identifying model shortcomings and computational obstacles. This chapter reports on one such collection, called the µMAG Standard Problems, used by the micromagnetic research community. The collection examines hysteresis, scaling across length scales, detailed computation of magnetic energies, magneto- dynamic trajectories, and spin momentum transfer. Each reference problem has proven useful in improving the micromagnetics state of the art. Recommendations distilled from this experience are presented. 1. Introduction The design and function of many modern devices rely on an understanding of pat- terns of magnetization in magnetic materials at the scale of nanometers. Examples include recording heads, field sensors, spin torque oscillators, and nonvolatile mag- netic memory (MRAM). To study such systems researchers employ micromagnetic models, which are continuum models of magnetic materials and magnetization pro- cesses at this scale. These models are encoded in software, and simulations compute predictions of magnetic behavior used both to design devices and to interpret mea- surements at the nanoscale. -
Ch. 2 Magnetostatics Ki-Suk Lee Class Lab
Tue Thur 13:00-14:15 (S103) Ch. 2 Magnetostatics Ki-Suk Lee Class Lab. Materials Science and Engineering Nano Materials Engineering Track Goal of this class Goal of this class Goal of this class Goal of this class Goal of this chapter We begin with magnetostatics, the classical physics of the magnetic fields, forces and energies associated with distributions of magnetic material and steady electric currents. The concepts presented here underpin the magnetism of solids. Magnetostatics refers to situations where there is no time dependence. 2.1 The magnetic dipole moment The elementary quantity in solid-state magnetism is the magnetic moment m. The local magnetization M(r ) fluctuates on an atomic scale – dots represent the atoms. The mesoscopic average, shown by the dashed line, is uniform. the local magnetization M(r,t ) which fluctuates wildly on a subnanometre scale, and also rapidly in time on a subnanosecond scale. But for our purposes, it is more useful to define a mesoscopic average <M(r,t )> over a distance of order a few Nanometres, and times of order a few microseconds to arrive at a steady, homogeneous, local magnetization M(r). The time-averaged magnetic moment δm in a mesoscopic volume δV is 2.1 The magnetic dipole moment Continuous medium approximation The representation of the magnetization of a solid by the quantity M(r) which varies smoothly on a mesoscopic scale. The concept of magnetization of a ferromagnet is often extended to cover the macroscopic average over a sample: According to Amp`ere, a magnet is equivalent to a circulating electric current; the elementary magnetic moment m can be represented by a tiny current loop. -
Magnetostatics and the Micromagnetics of Iron Whiskers
MAGNETOSTATICS AND THE MICROMAGNETICS OF IRON WHISKERS Dan S. Bloomberg B.A., University of California, Berkeley, 1967 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY , in the Department of Physics DAN S. BLOOMBERG 1973 SIMON FRASER UNIVERSITY March 1973 All rights reserved. This thesis may not be reproduced in whole or in part, by photocopy or other means, without permission of the author. APPROVAL Name: Dan S. Bloomberg Degree: Doctor of Philosophy Title of Thesis: Magnetostatics and the Micromagnetics of Iron Whiskers Examining Committee: Chairman: K.E. Rieckhoff -/ ~A.S.Arrott Senior Supervisor ' B.L. ones I J.C. Irwin W.F. Brown, Jr. External Examiner Professor of Electrical Engineering University of Minnesota Minneapolis, Minnesota Date Approved: March 22, 1973 PARTIAL COPYRIGHT LICENSE I hereby grant to Simon Fraser University the right to lend my thesis or dissertation (the title of which is shown below) to users of the Simon Fraser University Library, and to make partial or single copies only for such users or in response to a request from the library of any other university, or other educational institution, on its own behalf or for one of its users. I further agree that permission for multiple copying of this thesis for scholarly purposes may be granted by me or the Dean of Graduate Studies. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Title of ~hesis/~issertation: "Magnetostatics and the micromagnetic theory of iron whiskers" Author : (signature) Dan S .