MAGNETISM

Materials and Applications

Front Cover Photo:Courtesy of Pierre Molho, Laboratoire Louis Néel du CNRS, Grenoble, France.A computer hard disk drive, a device combining many state-of-the-art magnetictechnologies (courtesy of Seagate Corporation). The unit is set against a magneticdomain pattern in a garnet film, imaged through the mageneto-optical Faraday effect;the domain width is about 7 um (courtesy Pierre Molho, LaboratoireLouis Néel du CNRS, Grenoble, France).

MAGNETISM

Materials and Applications

Edited by

Étienne du TRÉMOLET de LACHEISSERIEDamien GIGNOUX

Michel SCHLENKER

Springer

eBook ISBN: 0-387-23063-7Print ISBN: 0-387-23000-9

Print ©2005 Springer Science + Business Media, Inc.

All rights reserved

No part of this eBook may be reproduced or transmitted in any form or by any means, electronic,

mechanical, recording, or otherwise, without written consent from the Publisher

Created in the United States of America

Boston

©2005 Springer Science + Business Media, Inc.

Visit Springer's eBookstore at: http://ebooks.kluweronline.comand the Springer Global Website Online at: http://www.springeronline.com

AUTHORS

Michel CYROT - Professor at the Joseph Fourier University of Grenoble, France

Michel DÉCORPS - Senior Researcher, INSERM (French Institute of Health andMedical Research), Bioclinical Magnetic Nuclear Resonance Unit, Grenoble

Bernard DIÉNY - Researcher and group leader at the CEA (French Atomic EnergyCenter), Grenoble

Etienne du TRÉMOLET de LACHEISSERIE - Senior Researcher, CNRS,Laboratoire Louis Néel, Grenoble

Olivier GEOFFROY - Assistant Professor at the Joseph Fourier University ofGrenoble

Damien GlGNOUX - Professor at the Joseph Fourier University of Grenoble

Ian HEDLEY - Researcher at the University of Geneva, Switzerland

Claudine LACROIX - Senior Researcher, CNRS, Laboratoire Louis Néel, Grenoble

Jean LAFOREST - Research Engineer, CNRS, Laboratoire Louis Néel, Grenoble

Philippe LETHUILLIER - Engineer at the Joseph Fourier University of Grenoble

Pierre MOLHO - Researcher, CNRS, Laboratoire Louis Néel, Grenoble

Jean-Claude PEUZIN - Senior Researcher, CNRS, Laboratoire Louis Néel, Grenoble

Jacques PIERRE - Senior Researcher, CNRS, Laboratoire Louis Néel, Grenoble

Jean-Louis PORTESEIL - Professor at the Joseph Fourier University of Grenoble

Pierre ROCHETTE - Professor at the University of Aix-Marseille 3, France

Michel-François ROSSIGNOL - Professor at the Institut National Polytechnique deGrenoble (Technical University)

Yves SAMSON - Researcher and group leader at the CEA (French Atomic EnergyCenter) in Grenoble

Michel SCHLENKER - Professor at the Institut National Polytechnique de Grenoble(Technical University)

Christoph SEGEBARTH - Senior Researcher, INSERM (French Institute of Healthand Medical Research), Bioclinical Magnetic Nuclear Resonance Unit, Grenoble

Yves SOUCHE - Research Engineer, CNRS, Laboratoire Louis Néel, Grenoble

Jean-Paul YONNET - Senior Researcher, CNRS, Electrical Engineering Laboratory,Institut National Polytechnique de Grenoble (Technical University)

Grenoble Sciences

“Grenoble Sciences” was created ten years ago by the Joseph Fourier University ofGrenoble, France (Science, Technology and Medicine) to select and publish originalprojects. Anonymous referees choose the best projects and then a Reading Committeeinteracts with the authors as long as necessary to improve the quality of themanuscript.

(Contact : Tél.: (33)4 76 51 46 95 - E-mail : Grenoble.Sciences@ujf-grenoble.fr)

The “Magnetism” Reading Committee included the following members :

V. Archambault, Engineer - Rhodia-Recherche, Aubervilliers, FranceE. Burzo, Professor at the University of Cluj, RumaniaI. Campbell, Senoir Researcher - CNRS, Orsay, FranceF. Claeyssen, Engineer - CEDRAT, Grenoble, FranceG. Couderchon, Engineer - Imphy Ugine Précision, Imphy, FranceJ.M.D. Coey, Professor - Trinity College, Dublin, IrelandA. Fert, Professor - INSA, Toulouse, FranceD. Givord, Senior Researcher - Laboratoire Louis Néel, Grenoble, FranceL. Néel, Professor, Nobel Laureate in Physics, Member of the French Academy ofScienceB. Raquet, Assistant Professor - INSA, Toulouse, FranceA. Rudi, Engineer - ECIA, Audincourt, FrancePh. Tenaud, Engineer - UGIMAG, St-Pierre d’Allevard, France

“Magnetism” (2 volumes) is an improved version of the French book published by“Grenoble Sciences” in partnership with EDP Sciences with support from the FrenchMinistry of Higher Education and Research and the “Région Rhône-Alpes”.

VI

BRIEF CONTENTS

I - FUNDAMENTALS

Foreword

Phenomenological approach to magnetismMagnetism, from the dawn of civilization to today - E. du Trémolet de Lacheisserie

Magnetostatics - D. Gignoux, J.C. Peuzin

Phenomenology of magnetism at the macroscopic scale - D. Gignoux

Phenomenology of magnetism at the microscopic scale - D. Gignoux

Ferromagnetism of an ideal system - M. Rossignol, M. Schlenker, Y. Samson

Irreversibility of magnetization processes, and hysteresis in real ferromagnetic materials:

the role of defects - M. Rossignol

1

2

3

4

5

6

Theoretical approach to magnetismMagnetism in the localised electron model - D. Gignoux

Magnetism in the itinerant electron model - M. Cyrot

Exchange interactions - C. Lacroix, M. Cyrot

Thermodynamic aspects of magnetism - M. Schlenker, E. du T. de Lacheisserie

7

8

9

10

Coupling phenomenaMagnetocaloric coupling and related effects - E. du Trémolet de Lacheisserie, M. Schlenker

Magnetoelastic effects - E. du Trémolet de Lacheisserie

Magneto-optical effects - M. Schlenker, Y. Souche

Magnetic resistivity, magnetoresistance, and the Hall effect - J. Pierre

11

12

13

14

AppendicesSymbols used in the text

Units and universal constants

Periodic table of the elements

Magnetic susceptibilities

Ferromagnetic materials

Special functions

Maxwell’s equations

1

2

3

4

5

6

7

General references

Index by material and by subject

II - MATERIALS AND APPLICATIONS

Foreword

Magnetic materials and their applicationsPermanent magnets - M. Rossignol, J.P. Yonnet

Soft materials for electrical engineering and low frequency electronics - O. Geoffroy, J.L. Porteseil

Soft materials for high frequency electronics - J.C. Peuzin

Magnetostrictive materials - E. du Trémolet de Lacheisserie

Superconductivity - M. Cyrot

Magnetic thin films and multilayers - B. Dieny

Principles of magnetic recording - J.C. Peuzin

Ferrofluids - P. Molho

15

16

17

18

19

20

21

22

Other aspects of magnetismMagnetic resonance imaging - M. Décorps, C. Segebarth

Magnetism of earth materials and geomagnetism - P. Rochette, I. Hedley

Magnetism and the Life Sciences - E. du Trémolet de Lacheisserie, P. Rochette

Practical magnetism and instrumentation - Ph. Lethuillier

23

24

25

26

AppendicesSymbols used in the text

Units and universal constants

Periodic table of the elements

Magnetic susceptibilities

Ferromagnetic materials

Economic aspects of magnetic materials - J. Laforest

1

2

3

4

5

6

General references

Index by material and by subject

VIII

TABLE OF CONTENTSII - MATERIALS AND APPLICATIONS

Foreword by Professor Louis Néel

Preface

Acknowledgements

XXI

XXIII

XXIV

MAGNETIC MATERIALS AND THEIR APPLICATIONS

15 - Permanent magnets1. Implementation of magnets

1.1. The two hysteresis loops of a material: magnetization loop M(H)and induction loop B(H)

1.2. Operation of an ideal permanent magnet within a systemLoad line and working point of a magnetStatic and dynamic operation of a permanent magnetThe maximum energy product (static operation)Free energy involved in the dynamic operation of a magnet

Performance parameters of real magnet materialsMagnetization and induction loops of various hard magnetic materialsThe maximum energy productPerformance parameters, and their range of variation

Oriented (textured) and isotropic magnetsMagnet classificationComparison of the magnetic behavior of oriented and isotropic magnets

Principal industrial magnet materialsThe various types of sintered and oriented magnets

AlNiCo magnetsFerrite magnetsSamarium-cobalt magnetsNeodymium-iron-boron magnets

Parameters and typical curvesSintered and oriented magnetsBonded magnets

Uses of permanent magnetsThe principal fields of permanent magnet applications

MiniaturizationPermanent field sourcesRepelling magnets

Properties of industrial magnetsPrincipal properties of the AlNiCo magnetsMain characteristics of ferrite magnetsMain properties of rare earth magnets

1.2.1.1.2.2.1.2.3.1.2.4.

1.3.1.3.1.1.3.2.1.3.3.

2.2.1.2.2.

3.3.1.

3.1.1.3.1.2.3.1.3.3.1.4.

3.2.3.2.1.3.2.2.

4.4.1.

4.1.14.1.2.4.1.3

4.2.4.2.1.4.2.2.4.2.3.

3

4

44578

1010101112

141415

171718181819191920

212121232324242526

Electromagnetic systemsThe evolution of motorsPermanent magnet actuators

Magnetomechanical systemsMagnetic bearingsMagnetic couplings

Field sourcesSensorsEddy current systemsField source

Modelling permanent magnet systemsClosed circuit calculationsOpen circuit calculationsNumerical methodsMagnet characteristics

Magnet materials: microstructure and preparation techniquesCoercivity and how to enhance it

Strong uniaxial anisotropyThe role of defects and the need for a microstructure

The magnet material must be reduced to fine particlesReduction into grains to suppress nucleationReduction into grains to increase remanence and the squareness of the M(H) loop

General principles of the processes used to prepare magnet microstructuresOriented sintered magnetsCoercive powders and bonded magnets

The basic materials for permanent magnetsMagnetic characteristics of 3d and 4f elementsvs the properties required to obtain a hard magnetic material

Magnetic moments and exchange interactions in rare earth and transition metalsMagnetocrystalline anisotropy of 3d and 4f elements

Transition metal based magnet materialsR-M intermetallic alloys (R = rare earth, M = transition metal)

R-M exchange coupling, via the d electronsR-M coupling = ferromagnetism or ferrimagnetismMagnetocrystalline anisotropy in R-M compoundswith uniaxial crystallographic structure: easy axis or easy plane

Review of intermetallic compoundsBinary compoundsTernary compoundsInterstitial ternary compounds

Magnetization reversal mechanismsMagnetization reversal in magnetic systems devoidof magnetocrystalline anisotropy: application to AlNiCo magnetsMagnetization reversal in systems with strong magnetocrystalline anisotropy:non-collective reversal in stages

Stages of the processThe driving forces of reversal: magnetic fields and thermal effects

The magnetization reversal fieldrelationship with the intrinsic magnetic properties of the principal phase

as a function of and local dipolar effectsas a function of the energy barrier for the critical mechanism

4.3.4.3.1.4.3.2.

4.4.4.4.1.4.4.2.

4.5.4.5.1.4.5.2.4.5.3.

4.6.4.6.1.4.6.2.4.6.3.4.6.4.

5.5.1.

5.1.1.5.1.2.

5.2.5.2.1.5.2.2.

5.3.5.3.1.5.3.2.

6.6.1.

6.1.1.6.1.2.

6.2.6.3.

6.3.1.6.3.2.6.3.3.

6.4.6.4.1.6.4.2.6.4.3.

7.7.1.

7.2.

7.2.1.7.2.2.

7.3.

7.3.1.7.3.2.

272829303031323233343636363739

39394040404141424244

45

45464748515155

5657586263

64

64

666667

676869

X

Which mechanism determines magnetization reversal?Analysis of the initial magnetization curve, particularly the initial susceptibilityObservation of domains and domain wall motionin the thermally demagnetised stateVariation of the reversal field with the direction of the applied field:Modelling of the different mechanisms involvedin non-collective magnetization reversal

Exercises

Solution to the exercises

References

16 - Soft materials for electrical engineering and low frequency electronicsGeneral presentation of soft materials

The properties required of a soft materialRole of structural and electromagnetic characteristics

PolarizationPermeabilityEnergy dissipation

Energy loss analysisMacroscopic aspectsCalculation of losses in a conductor

Losses in rotating or trapezoidal field

Iron based crystalline materialsIron and soft steelsClassical iron-silicon alloysFe-Si sheets with non oriented (NO) grains

Magnetic characteristicsApplicationsEvolution and prospects of NO sheets

Grain-oriented (GO) Fe-Si sheetsDomain structure optimizationMagnetic characteristics

Thin iron-silicon sheetsHigh silicon content alloys

Alloys obtained by fast solidificationDiffusion enriched alloys

Iron-nickel and iron-cobalt alloysIron-nickel family

Alloys around 30% NiAlloys around 50% NiAlloys around 80% Ni (Permalloys)

Iron-cobalt alloys

Soft ferritesElectromagnetic properties

Saturation polarizationCurie temperatureAnisotropyMagnetostrictionResistivityPermeability - cutoff frequency product

7.4.7.4.1.7.4.2.

7.4.3.7.4.4.

1.1.1.1.2.

1.2.1.1.2.2.1.2.3.

1.3.1.3.1.1.3.2.

1.4.

2.2.1.2.2.2.3.

2.3.1.2.3.2.2.3.3.

2.4.2.4.1.2.4.2.

2.5.2.6.

2.6.1.2.6.2.

3.3.1.

3.1.1.3.1.2.3.1.3.

3.2.

4.4.1.

4.1 .1.4.1.2.4.1.3.4.1.4.4.1.5.4.1.6.

7171

7273

75

76

81

86

89

89909090919292929396

9696979999

100100101102103104105105107

108108109109110111

112112112112113113113113

XI

Applications of ferritesPower electronicsLow power applications

Amorphous alloysGeneral characteristicsMain classes of soft amorphous alloys

High polarization alloysLow magnetostriction alloys

Applications of amorphous alloys

Nanocrystalline materialsElectromagnetic characteristics

PolarizationAnisotropyMagnetostrictionResistivityUniaxial induced anisotropy

Random anisotropy modelApplications of nanocrystalline materials

Energy conversion at industrial frequencies (50-400 Hz)Distribution transformersRotating machines

A refresher on magnetic system energyApplication to the study of some structuresThe main classes of machinesSoft magnetic materials used in rotating machines

ActuatorsAn example of a rotating actuator: stepping machine with variable reluctanceChoice criteria, orders of magnitude

Energy transformation in power electronicsSmoothing inductances, and components for inductive energy storageRequirements associated with high frequencyControl-power interfacing

Maximum pulse lengthResponse timeComment on the static switch

Exercises: study of a voltage stabilizing device using a saturable inductance

Solutions to the exercices

References

17 - Soft materials for high frequency electronicsComplex susceptibility and permeability

Isotropic complex susceptiblity and permeabilityPhysical meaning of andGeneral dynamic regimeKramers-Kronig relations

Anisotropic materials. Complex susceptibility and permeability tensors

Measuring the complex susceptibility and permeabilityInternal and external susceptibilities

External susceptibility in a simple caseEffect of the demagnetising field on the drifts and lossesSkin effect and dimensional resonance

4.2.4.2.1.4.2.2.

5.5.1.5.2.

5.2.1.5.2.2.

5.3.

6.6.1.

6.1.1.6.1.2.6.1.3.6.1.4.6.1.5.

6.2.6.3.

7.7.1.7.2.

7.2.1.7.2.2.7.2.3.7.2.4.

8.8.1.8.2.

9.9.1.9.2.9.3.

9.3.1.9.3.2.9.3.3.

1.1.1.

1.1.1.1.1.2.1.1.3.

1.2.

2.2.1.

2.1.1.2.1.2.2.1.3.

114114114

114115115115116116

117118118118118119119119121

122123127127128132134

134135141

143143144146146146147

148

151

153

155

155156156157158158

159159160160161

XII

Reciprocity theoremMeasuring by perturbation of a coilTwo coil measurementFrequency limitations in coil methodsMeasuring toroidal samples

Elementary susceptibility mechanismsRotation mechanism

Isotropic rotation (or uniaxial symmetry)Anisotropic rotation

Wall mechanismBallistic behavior - Döring massIntroducing damping - Wall mobilityEquation of motion for an isolated plane wallGeneralization to curved wallsDiffusion relaxationDisaccommodation

Susceptibility in the demagnetised state: the homogenization problemThe approximation of additivity or of the mean

Snoek’s modelThe model of Globus et al.

Effective medium modelWall contribution and rotation contribution

Susceptibility in the saturated state - Magnetostatic modesCircular susceptibilities and permeabilities - GyrotropyUniform magnetostatic resonanceNon uniform resonance: magnetostatic modesThe role of exchange interaction: spin waves

An overview of radio-frequency materials and applicationsSpinelsPlanar hexaferritesApplications in linear inductive components

Overview of microwave materials and applicationsThe ferrimagnetic garnetsMicrowave applications

Non-reciprocal devicesTunable resonatorMicrowave absorbers

Appendix: the effective medium method

Exercises

Solutions to the exercises

References

18 - Magnetostrictive materialsThe Invar and Elinvar family

Controlled thermal expansion alloysAlloys with constant elastic moduli

Magnetostrictive materials for actuatorsMaterials with high anisotropic magnetostrictionTerfenol-D

2.2.2.3.2.4.2.5.2.6.

3.3.1.

3.1.1.3.1.2.

3.2.3.2.1.3.2.2.3.2.3.3.2.4.3.2.5.3.2.6.

4.4.1.

4.1.1.4.1.2.

4.2.4.3.

5.5.1.5.2.5.3.5.4.

6.6.1.6.2.6.3.

7.7.1.7.2.

7.2.1.7.2.2.7.2.3.

1.1.1.1.2.

2.2.1.2.2.

162162163164164

166167168171173174176176177177178

178179179180181183

184184185187189

190191193194

197197198198202203

204

209

210

210

213

213213215

216216216

XIII

Use of Terfenol-D in actuatorsLinear actuatorDifferential actuatorWiedemann effect actuatorsMagnetostrictive linear motorMagnetostrictive rotary motorsSonar

Sensor materialsMetglas 2605SCSensors based on inverse magnetoelastic effects

Force sensorUltrasensitive magnetometryInverse Wiedemann effect torquemeter

Sensors based on direct magnetoelastic effectsMagnetostrictive magnetometersPosition detector

Integrated actuators and sensors

Conclusions and perspectives

Exercises

Solutions to the exercises

References

19 - SuperconductivityIntroduction

Definition of superconductivity

Some fundamental properties of superconductorsThermodynamic critical field and critical currentCharacteristic lengths

Physical effects related to the phaseFlux quantization in a ringJosephson effectAC Josephson effectDynamics of a shunted junction

SQUIDsThe dc SQUIDThe rf SQUIDThe SQUID in practice

Type-I and type-II superconductorsCritical fields and vorticesThe Abrikosov latticeCritical current in type-II superconductorsVortex pinning

Superconducting materials

Applications

References

2.3.2.3.1.2.3.2.2.3.3.2.3.4.2.3.5.2.3.6.

3.3.1.3.2.

3.2.1.3.2.2.3.2.3.

3.3.3.3.1.3.3.2.

4.

5.

1.

2.

3.3.1.3.2.

4.4.1.4.2.4.3.4.4.

5.5.1.5.2.5.3

6.6.1.6.2.6.3.6.4.

7.

8.

221221222222223224225

225226227227228228229229230

230

231

232

232

234

235

235

236

237237238

238238239241241

242242244245

246246248249250

251

251

253

XIV

20 - Magnetic thin films and multilayersFrom control of the local environment to control of the physical properties

Preparation and nanostructure of magnetic thin films and multilayersIntroductionExperimental techniques most commonly used to preparemagnetic thin films and multilayers

SputteringMolecular beam epitaxy (MBE)Chemical and structural methods for characterising thin films and multilayers

Magnetism of surfaces, interfaces and thin filmsIncrease in the magnetic moment at the surface of a transition metalSurface magnetism in materials not possessing a moment in the bulkEffects induced by the substrate on the magnetism of ultrathin epitaxic filmsEffect of reduced dimensionality on magnetic phase transitionsMagnetic anisotropy of thin films

Shape anisotropyMagnetocrystalline anisotropyMagnetoelastic anisotropyEffect of roughness and interdiffusion

Coupling mechanisms in magnetic multilayersDirect ferromagnetic coupling by pinholes or by dipolar interactionsCoupling across a non-magnetic film in multilayers consistingof alternating ferromagnetic transition metal and non-magnetictransition or noble metal layers (example Co/Cu)Interfacial coupling between ferromagnetic transition metal films and rare earth films

Transport properties of thin films and multilayersElectronic transport in metals

Classical imageDescription of electrical conductivity in the frameworkof a band model, the free electron gas modelThe two current model, spin dependent scattering in magnetic transition metals

Finite size effect on the conductivity of metallic thin filmsMagnetoresistance in thin films and metallic magnetic multilayers

Anisotropy of the magnetoresistancein ferromagnetic transition metals in bulk and thin film formGiant magnetoresistance (GMR)The physical origin of giant magnetoresistanceDifferent types of giant magnetoresistive multilayers

Spin polarised electron tunnellingApplications of magnetic thin film and multilayers

Magnetic recording mediaMagneto-optical recording mediaSoft materialsMagnetostrictive materialsMaterials for microwave applicationsMagnetoresistive materials

Spin electronics and magnetic nanostructures

References

1.

2.2.1.2.2.

2.2.1.2.2.2.2.2.3.

3.3.1.3.2.3.3.3.4.3.5.

3.5.1.3.5.2.3.5.3.3.5.4.

4.4.1.4.2.

4.3.

5.5.1.

5.1.1.5.1.2.

5.1.3.5.2.5.3.

5.3.1.

5.3.2.5.3.3.5.3.4.

5.4.5.5.

5.5.1.5.5.2.5.5.3.5.5.4.5.5.5.5.5.6.

6.

255

255

258258

259259261263

263264265265266268270270271272

272273

274275

278278278

279281282284

284285287288291295295296297297298298

300

301

XV

21 - Principles of magnetic recordingIntroduction

Overview of the various magnetic recording processesAnalog recordingDigital recordingPerpendicular recordingMagneto-optical recordingDomain propagation memory

Recording mediaParticulate media

Stoner-Wohlfarth modelSuperparamagnetism in particulate media

Granular media, metallic thin filmsContinuous media: epitactic single crystal films and homogeneous amorphous films

The write processField produced by a magnetic headStability of written magnetization patternsWriting a transition with a Karlqvist head

The read processInductive readoutMagnetoresistive readout

Concluding remark

References

22 - FerrofluidsIntroduction

Characteristics of a ferrofluidStabilityTypes of ferrofluids and their production

Surfacted ferrofluidsIonic ferrofluids

Properties of ferrofluidsSuperparamagnetismInteractions between particles: formation of chainsViscosityOptical birefringence

ApplicationsLong-life sealsLubrication - Heat transferPrintingAccelerometers and inclinometersPolishingDampers and shock absorbersApplications of the optical properties of ferrofluidsBiomedical applicationsForeseeable developments

Surface instabilities

References

1.

2.2.1.2.2.2.3.2.4.2.5.

3.3.1.

3.1.1.3.1.2.

3.2.3.3.

4.4.1.4.2.4.3.

5.5.1.5.2.

6.

1.

2.2.1.2.2.

2.2.1.2.2.2.

3.3.1.3.2.3.3.3.4.

4.4.1.4.2.4.3.4.4.4.5.4.6.4.7.4.8.4.9.

5.

305

306

307307310311311312

314314314315316318

318319321323

326326329

335

335

337

337

338338339339340

340340342343344

345345345345345346346346347347

348

351

XVI

OTHER ASPECTS OF MAGNETISM

23 - Magnetic resonance imagingThe physical basis of nuclear magnetic resonance

Energy levels in a magnetic fieldA collection of nuclei in a magnetic fieldRadiofrequency pulsesSpin lattice relaxationFree precession signalChemical shiftSpin echoesThe NMR experiment

Magnetic Resonance ImagingSelective pulses: the linear response approximationField gradientsExcitation of a system of spins in the presence of a gradient: slice selectionImaging: the reciprocal spaceContrast

An example of MRI application: cerebral activation imagingHaemodynamic and blood oxygenation changes induced by neuronal activationBOLD contrast: biophysical mechanisms

Effects of magnetic susceptibility in tissuesSusceptibility effects, and the NMR signal: BOLD contrast

The fMRI sequencesThe fMRI protocol and the processing of the fMR imagesExamples of applications

VisionCognitionMotor function

References

24 - Magnetism of earth materials and geomagnetismIntroduction

Experimental techniquesGeneralitiesMeasurement of remanent magnetization (NRM)Susceptibility and anisotropy measurementsCharacterization of magnetic mineralsMeasurement of magnetic fields

Intrinsic magnetic properties of earth materialsIntroductionMagnetic minerals

OxidesSulphidesOther magnetic mineralsParamagnetic minerals

Applications of magnetic mineralogy to the earth sciences

Magnetic anisotropy: application to the determination of rock fabric

1.1.1.1.2.1.3.1.4.1.5.1.6.1.7.1.8.

2.2.1.2.2.2.3.2.42.5.

3.3.1.3.2.

3.2.1.3.2.2.

3.3.3.4.3.5.

3.5.1.3.5.2.3.5.3.

1.

2.2.1.2.2.2.3.2.4.2.5.

3.3.1.3.2.

3.2.1.3.2.2.3.2.3.3.2.4.

3.3.

4.

355

355355357357358359360361362

362363366367368370

371371373374376380381382382383384

385

387

387

388388389390391392

392392394394396396397397

399

XVII

Natural remanent magnetizationPrinciples of palaeomagnetismNRM acquisition processes

Thermoremanent magnetization (TRM)Crystallization remanent magnetization (CRM)Viscous remanent magnetization (VRM)Detrital remanent magnetization (DRM)Piezoremanent magnetization (PRM)

NRM analysis techniques

Present geomagnetic fieldGeneralitiesCore fieldShort wavelength spatial variations: crustal magnetizationRapid variations: external field

The ancient field recorded by palaeomagnetism

Origin of the core field: dynamo theory

Palaeomagnetic applicationsTectonics and continental driftDating

Extraterrestrial magnetism

References

25 - Magnetism and the Life SciencesMagnetic properties of organic matter

Inert organic materialsLiving organic materialsOrganometallic materials and biology

HemoglobinFerritin and hemosiderinFibrin

Magnetic minerals encapsulated in organic matterAlgae and magnetic bacteriaAnimal magnetismEncapsulated Microspheres

Human sensitivity to magnetic fields

Magnetic exploration techniques for living organismsResonance methodsDetection of magnetic fields produced by living tissuesMagnetic marking techniquesMagnetic sensors

Magnetic techniques for intervention in vivoCardiac valveMagnetic manipulation of cathetersDental careMicro-actuatorsUse of magnetic bacteriaUse of other magnetic materialsMagnetotherapy

Conclusions

References

5.5.1.5.2.

5.2.1.5.2.2.5.2.3.5.2.4.5.2.5.

5.3.

6.6.1.6.2.6.3.6.4.

7.

8.

9.9.1.9.2.

10.

1.1.1.1.2.1.3.

1.3.1.1.3.2.1.3.3.

1.4.1.4.1.1.4.2.1.4.3.

1.5.

2.2.1.2.2.2.3.2.4.

3.3.1.3.2.3.3.3.4.3.5.3.6.3.7.

4.

403403404404404405405405406

407407408409411

413

415

417417420

421

423

425

425425426427427427428428428429429430

431431431432433

433433435436436436437437

438

438

XVIII

26 - Practical magnetism and instrumentationMagnetization measurement techniques

Reciprocity theoremMeasurement of soft materials

Measurement of a toroidal sampleEpstein permeameter

Measurement of the magnetization of hard materials or of weakly magnetic materialsForce methodsFlux methodsHartshorn BridgeMeasurement of anisotropyCalibration of magnetization

Generation of magnetic fieldsMagnetic field generation without using magnetic materials

Calculation of the field produced by a solenoid at any point in spaceThe solenoidSuperconducting coilBitter coilsHybrid techniquesPulsed fields

Generation of magnetic fields using magnetic materialsSome useful approximationsFlux channeling - case of a closed circuitFlux channelingPermanent magnetsAlmost closed U-shaped magnetThe magic cylinder

Measurement of magnetic fieldsHall ProbeFlux gate magnetometer

Reference

APPENDICES

Symbols used in the text

Units and universal constantsConversion of MKSA units into the CGS system, and other unit systems of common use

Some fundamental physical constants

Periodic table of the elements

Magnetic susceptibilities

Ferromagnetic materials

Economic aspects of magnetic materialsIntroduction

Hard materials for permanent magnetsThe applications for magnetsThe main families of permanent magnets

1.1.1.1.2.

1.2.1.1.2.2.

1.3.1.3.1.1.3.2.1.3.3.1.3.4.I.3.5.

2.2.1.

2.1.1.2.1.2.2.1.3.2.1.4.2.1.5.2.1.6.

2.2.2.2.1.2.2.2.2.2.3.2.2.4.2.2.5.2.2.6.

3.3.1.3.2.

1.

2.1.

2.

3.

4.

5.

6.1.

2.2.1.2.2.

441

441441442443444445445447455456456

456457457458458460460461462462463464466468468

469469470

472

475

479

479

480

481

483

487

489

489

490490490

XIX

Bonded magnetsGeographical distribution

Soft materialsSoft ironIron-silicon alloysSpecial alloysHigh frequency materials

Materials for magnetic recording

Other magnetic materialsMagnetostrictive materialsFerrofluids

General references

Index by material

Index by subject

2.3.2.4.

3.3.1.3.2.3.3.3.4.

4.

5.5.1.5.2.

492492

492492493493493

493

494494494

495

497

503

XX

FOREWORD

Thousands of years before our time, our ancestors already knew about the amazingproperties of lodestone, or magnetite. Ever since, man has been fascinated by magneticphenomena, especially because of their action at a distance. They are foundeverywhere in our daily lives: in refrigerator doors, cars, cellphones, suspensionsystems for high speed trains etc. In pure science they are present at all scales, fromelementary particles through to galaxy clusters, not forgetting their role in the structureand history of our Earth.

The last thirty years have seen considerable progress in most of these fields, whetherfundamental or technological. The purpose of this book is to present this progress. Itis the collective work of faculty members and researchers, most of whom work inlaboratories in Grenoble (Universities, CNRS, CEA), often in close cooperation withlocal industry, and the large international organizations established in the Grenoblearea: Institut Laue-Langevin, ESRF (large European synchrotron), etc. This is nosurprise, since activities concerning Magnetism have consistently been supported inGrenoble ever since the beginning of the century.

Most of the chapters are accessible to the University graduate in science. Thosenotions which require a little more maturity do not need to be fully mastered to be ableto understand what comes next. This treatise should be read by all who intend to workin the field of magnetism, such an open-ended field, rich in potential for furtherdevelopment.

New magnets, with higher performance and lower cost, will surely be found. Themagnetic properties of materials containing unfilled electronic shells are not yet fullyunderstood. Hysteresis plays a key role in irreversible effects. While its behavior isfairly well understood both in magnetic fields which are small with respect to thecoercive field, and in very strong fields near saturation, the processes occurring withinthe major loop have not yet been very well described. When hysteresis depends on thecombined action of two variables, such as magnetic field and very high pressure, weknow nothing. How are we, for instance, to predict the magnetic state of a submarinecruising at great depth, depending on its diving course?

French scientists, with Pierre Curie, Paul Langevin and Pierre Weiss, played apioneering role in magnetism. They will certainly have worthy successors, notably inbiomagnetism in a broad sense.

This work includes interesting features: exercises with solutions, referencesfortunately restricted to the best papers and books, and various appendices: lists of

symbols, special functions, properties of various materials, economic aspects, and, lastbut not least, a very necessary summary of units, which the dual coulombic-amperianpresentation made so unnecessarily complicated and unpalatable in the past.

I believe this book should satisfy a broad readership, and be a valuable document tostudents, researchers, and engineers. I wish it a lot of success.

Louis NEELNobel Laureate in Physics,

Member of the French Academy of Science

XXII

PREFACE

Magnetic materials are all around us, and understanding their properties underliesmuch of today’s engineering efforts. The range of applications in which they arecentrally involved includes audio, video and computer technology, telecommunications,automotive sensors, electric motors at all scales, medical imaging, energy supply andtransportation, as well as the design of stealthy airplanes.

This book deals with the basic phenomena that govern the magnetic properties ofmatter, with magnetic materials, and with the applications of magnetism in science,technology and medicine.

It is the collective work of twenty one scientists, most of them from Laboratoire LouisNéel in Grenoble, France. The original version, in French, was edited by Etienne duTrémolet de Lacheisserie, and published in 1999. The present version involves, beyondthe translation, many corrections and complements.

This book is meant for students at the undergraduate and graduate levels in physicsand engineering, and for practicing engineers and scientists. Most chapters includeexercises with solutions.

Although an in-depth understanding of magnetism requires a quantum mechanicalapproach, a phenomenological description of the mechanisms involved has beendeliberately chosen in most chapters in order for the book to be useful to a widereadership. The emphasis is placed, in the part devoted to the atomic aspects ofmagnetism, on explaining, rather than attempting to calculate, the mechanismsunderlying the exchange interaction and magnetocrystalline anisotropy, which lead tomagnetic order, hence to useful materials. This theoretical part is placed, in volume I,between a phenomenological part, introducing magnetic effects at the atomic,mesoscopic and macroscopic levels, and a presentation of magneto-caloric, magneto-elastic, magneto-optical and magneto-transport coupling effects. Volume II, dedicatedto magnetic materials and applications of magnetism, deals with permanent magnet(hard) materials, magnetically soft materials for low-frequency applications, then forhigh-frequency electronics, magnetostrictive materials, superconductors, magnetic thinfilms and multilayers, and ferrofluids. A chapter is dedicated to magnetic recording.The role of magnetism in magnetic resonance imaging (MRI), and in the earth and thelife sciences, is discussed. Finally, a chapter deals with instrumentation for magneticmeasurements. Appendices provide tables of magnetic properties, unit conversions,useful formulas, and some figures on the economic place of magnetic materials.

We will appreciate constructive comments and indications on errors from readers, viathe web site http://lab-neel.grenoble.cnrs.fr/magnetism-book

ACKNOWLEDGMENTS

We are grateful for their helpful suggestions to the members of the ReadingCommittee who worked on the original French edition: V. ARCHAMBAULT (Rhodia-Recherche), E. BURZO (University of Cluj-Napoca, Rumania), I. CAMPBELL

(Laboratoire de Physique des Solides, Orsay), F. CLAEYSSEN (CEDRAT, Grenoble),J.M.D. COEY (Trinity College, Dublin), G. COUDERCHON (Imphy Ugine Précision,Imphy), A. FERT (INSA, Toulouse), D. GIVORD (Laboratoire Louis Néel), L. NEEL,Nobel Laureate in Physics (who passed away at the end of 2000), B. RAQUET (INSA,Toulouse), A. RUDI (ECIA, Audincourt), and P. TENAUD (UGIMAG, St-Pierred’Allevard). The input of many colleagues in Laboratoire Louis Néel or Laboratoired’Electrotechnique de Grenoble was also invaluable: we are in particular gratefulto R. BALLOU, B. CANALS, J. CLEDIERE, O. CUGAT, W. WERNSDORFER. Criticalreading of various chapters by A. FONTAINE, R.M. GALERA, P.O. JUBERT,K. MACKAY, C. MEYER, P. MOLLARD, J.P. REBOUILLAT, D. SCHMITT andJ. VOIRON helped considerably. Zhang FENG-YUN kindly translated a document fromthe Chinese, J. TROCCAZ gave helpful advice in biomagnetism, D. FRUCHART,M. HASSLER and P. WOLFERS provided figures, and P. AVERBUCH gave usefuladvice on the appendix dealing with the economic aspects.

We also would like to thank all our fellow authors for their flawless cooperation inchecking the translated version, and often making substantial improvements withrespect to the original edition. We are happy to acknowledge the colleagues who,along with the two of us, took part in the translation work: Elisabeth ANNE,Nora DEMPSEY, Ian HEDLEY, Trefor ROBERTS, Ahmet TARI, and Andrew WILLS.

We enjoyed cooperating with Jean BORNAREL, Nicole SAUVAL, Sylvie BORDAGE andJulie RIDARD at Grenoble Sciences, who published the French edition and preparedthe present version.

Damien GIGNOUX - Michel SCHLENKER

XXIV