EE206 S4 MS Module on motor machines 4.pdf

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1. MAGNETIC MATERIALS
MODULE 4

2. MAGNETIC MATERIALS -TERMS
•MagneticSusceptibility:Ratioofintensityofmagnetisation
producedinthesampletothemagneticfieldintensitywhich
producesmagnetization.Ithasnounits.
χ =
??????
??????
•Magnetization:Theprocessofconvertinganonmagneticmaterial
toamagneticmaterial.
•Intensityofmagnetization:Itismagneticmomentperunitvolume.
•Relativepermeability:Theratiooffluxdensityproducedina
materialtothefluxdensityproducedinvacuumbythesame
magnetisingforce.

3. MAGNETIC MATERIALS -TERMS
•Magneticflux(Φ):Thetotalno:ofmagneticlinesofforceina
magneticfield(unit-Weber)
•Magneticfluxdensity(B):Magneticfluxperunitareaatright
anglestothedirectionofflux.(Wb/??????
2
)
•Magneticfieldintensity(H):Magnetomotiveforceperunitlength
ofthemagneticcircuit.Itisalsocalledmagneticfieldstrengthor
magnetizingforce.(A-turns/m)
•Permeability(µ):Theabilityofamaterialtoconductmagneticflux
throughit.(H/m)

4. A moving electric charge is responsible for Magnetism.
ORIGIN OF PERMENANT MAGNETIC DIPOLES

5. ORIGIN OF PERMENANT MAGNETIC DIPOLES
ORBITAL MOMENTUM
ORBITAL SPIN

6. Diamagnetic–materialswhichlackpermanentdipolesarecalled
diamagnetic
Paramagnetic–ifthepermanentdipolesdonotinteractamong
themselves,thematerialisparamagnetic
Ferromagnetic–iftheinteractionamongpermanentdipolesisstrong
suchthatallthedipoleslineupinparallel,thematerialisferromagnetic
Antiferromagnetic–ifthepermanentdipoleslineupinantiparallel
direction,thematerialisantiferromagnetic
Ferrimagnetic–antiparallelwithunequalmagnitude
CLASSIFICATION OF MAGNETIC MATERIALS

7. CLASSIFICATION OF MAGNETIC MATERIALS
DIAMAGNETIC MATERIALS
•Nopermanentdipolesarepresentsonetmagneticmomentiszero.
•Dipolesareinducedinthematerialinpresenceofexternalmagneticfield.
•Themagnetizationbecomeszeroonremovaloftheexternalfield.
•Magneticdipolesinthesesubstancestendtoaligninoppositiontotheappliedfield.
•Hence,theyproduceaninternalmagneticfieldthatopposestheappliedfieldand
thesubstancetendstorepeltheexternalfieldaroundit.
•Thisreducesthemagneticinductioninthespecimen.

8. CLASSIFICATION OF MAGNETIC MATERIALS
DIAMAGNETIC MATERIALS
•Magneticsusceptibilityissmallandnegative.
•Relativepermeabilityislessthanone.
•Itispresentinallmaterials,butsinceitissoweakitcanbeobserved
onlywhenothertypesofmagnetismaretotallyabsent.
•Ex:Gold,water,mercury,B,Si,P,S,ionslikeNa+,Cl-andtheirsalts,
diatomslikeH2,N2,..

9. CLASSIFICATION OF MAGNETIC MATERIALS
DIAMAGNETIC MATERIALS
Theyrepelthemagneticlinesofforce.Theexistenceofthisbehaviorina
diamagneticmaterialisshown
Normal conductors
Diamagnetic materials

10. CLASSIFICATION OF MAGNETIC MATERIALS
PARAMAGNETIC MATERIALS
•Iftheorbital'sarenotcompletelyfilledorspinsarenotbalanced,anoverall
smallmagneticmomentmayexist
•Themagneticdipolestendtoalignalongtheappliedmagneticfieldand
thusreinforcetheappliedmagneticfield.
•Suchmaterialsgetfeeblymagnetizedinthepresenceofamagneticfield
i.e.thematerialallowsfewmagneticlinesofforcetopassthroughit.
•Themagnetizationdisappearsassoonastheexternalfieldisremoved.

11. CLASSIFICATION OF MAGNETIC MATERIALS
PARAMAGNETIC MATERIALS
•Themagnetization(M)ofsuchmaterialswasdiscoveredbyMadam
Curieandisdependentontheexternalmagneticfield(B)and
temperatureTas:
χ=
??????
??????
where,C=CurieConstant
•Theorientationofmagneticdipolesdependsontemperatureandapplied
field.
•Relativepermeabilityµr>1
•Susceptibilityisindependentofappliedmagneticfieldanddependson
temperature

12. CLASSIFICATION OF MAGNETIC MATERIALS
PARAMAGNETIC MATERIALS
•Susceptibilityissmallandpositive
•Thesematerialsareusedinlasers.
•Ex:Liquidoxygen,sodium,platinum,saltsofironandnickel,rareearthoxides

13. CLASSIFICATION OF MAGNETIC MATERIALS
FERROMAGNETIC MATERIALS
•Theyexhibitstrongestmagneticbehavior.
•Permanentdipolesarepresentwhichcontributesanetmagneticmoment.
•Possessspontaneousmagnetizationbecauseofinteractionbetweendipoles
•OriginformagnetisminFerromagneticmaterialsareduetoSpinmagnetic
moment.Allspinsarealignedparallel&insamedirection
•Whenplacedinexternalmagneticfielditstronglyattractsmagneticlinesofforce.
•Thedomainsreorientthemselvestoreinforcetheexternalfieldandproducea
stronginternalmagneticfieldthatisalongtheexternalfield.

14. CLASSIFICATION OF MAGNETIC MATERIALS
FERROMAGNETIC MATERIALS
•Mostofthedomainscontinuestobealignedinthedirectionofthemagnetic
fieldevenafterremovalofexternalfield.
•Thus,themagneticfieldofthesemagneticmaterialspersistsevenwhenthe
externalfielddisappears.
•ThispropertyisusedtoproducePermanentmagnets.
•Transitionmetals,iron,cobalt,nickel,neodymiumandtheiralloysareusually
highlyferromagneticandareusedtomakepermanentmagnets.

15. CLASSIFICATION OF MAGNETIC MATERIALS
FERROMAGNETIC MATERIALS
•Susceptibilityislargeandpositive,itisgivenbyCurieWeissLaw;
χ=
??????
??????−θ
where,CisCurieconstant&θisCurie
temperature.
•WhentemperatureisgreaterthanCurietemperaturethenthematerialgets
convertedintoparamagnetic.
•TheypossessthepropertyofHysteresis.

16. CLASSIFICATION OF MAGNETIC MATERIALS
FERROMAGNETIC MATERIALS
Domaintheoryofferromagneticmaterials:
Amagneticdomainisaregionwithinamagneticmaterialinwhichthe
magnetizationisinauniformdirection.
Ferromagneticmaterialstendtoformmagneticdomains.
Eachdomainismagnetizedinadifferentdirection.
Applyingafieldchangesdomainstructure.Domainswithmagnetizationin
directionoffieldgrow.(Domaingrowth)
Domainstructureminimizesenergyduetostrayfields.

17. CLASSIFICATION OF MAGNETIC MATERIALS
Domaintheoryofferromagneticmaterials:
Domainswithmagnetizationinthedirectionoffieldgrowwhileother
domainsshrink.
Applyingverystrongfieldscansaturatemagnetizationbycreatingsingle
domain.(Domainrotation)
Un-magnetized Magnetized by domain growth Magnetized by domain rotation

18. CLASSIFICATION OF MAGNETIC MATERIALS
FERROMAGNETIC MATERIALS
Hysteresis:
ThepropertyofFerroMagneticmaterialswhichgivestherelation
betweenMagnetizationandthestrengthofMagneticfieldiscalled
Hysteresis.
Themagnetizationofthespecimenincreasesfromzerotohighervalues
andattainsitsmaximumvalueatapointreferredtoasSaturation
Magnetization.
WhenwefurtherincreaseMagneticfieldHthereisnofurtherincrement
inMagneticmoment.

19. CLASSIFICATION OF MAGNETIC MATERIALS
FERROMAGNETIC MATERIALS
Hysteresis:
WhenwedecreaseMagneticfieldHtoZero,theMagnetizationMattains
pointQreferredtoasResidualMagnetization,Mr.
FurtherifwechangetheMagneticfieldfromzerotonegativevalues,the
MagnetizationofmaterialbecomeszeroatapointR,wheremagneticfield
HcisreferredasCoercivityofthespecimen.
IfweincreaseMagneticfieldHinreversedirectionMagnetizationof
materialreachesitspeakvalueatapointsS.
Theareaofloopindicatestheamountofenergywastedinonecycleof
operation

20. CLASSIFICATION OF MAGNETIC MATERIALS
FERROMAGNETIC MATERIALS
Hysteresis:
Hysteresisloop-Thelooptracedoutbymagnetizationinaferromagnetic
orferrimagneticmaterialasthemagneticfieldiscycled

21. CLASSIFICATION OF MAGNETIC MATERIALS
ANTIFERROMAGNETIC MATERIALS
•Thespinalignmentisinantiparallelmanner.
•Susceptibilityissmallandpositiveanditdependsontemperature.
•Initiallysusceptibilityincreaseswithincreaseintemperatureandbeyond
Neeltemperaturethesusceptibilitydecreaseswithtemperature.
•Theantiparallelalignmentexistsinmaterialbelowacriticaltemperature
knownasNeeltemperature
•AtNeeltemperaturesusceptibilityismaximum.

22. CLASSIFICATION OF MAGNETIC MATERIALS
ANTIFERROMAGNETIC MATERIALS
•Susceptibility,χ=
??????
??????+θ
•Examples:Mn,Cr,FeO,MnO,Cr2O3andsaltsoftransitionelements.

23. CLASSIFICATION OF MAGNETIC MATERIALS
FERRIMAGNETICMATERIALS
•Thespinalignmentisantiparallelbuthavedifferentmagnitude.
•Sotheypossessnetmagneticmomentwhichproducealargemagnetizationeven
forasmallappliedexternalfield.
•Itisalsocalledferrites.
•Susceptibilityisverylargeandpositive.
•Examples:ferrousferrite,nickelferrite

24. CLASSIFICATION OF MAGNETIC MATERIALS
Comparison:

25. CURIE –WEISS LAW
•TheCurie–Weisslawdescribesthemagneticsusceptibilityχofferromagnetic
materialsattemperaturesabovetheCuriepoint:
χ =
??????
??????−????????????
where,C=MaterialspecificCurieconstant,T=Absolutetemperature,Tc=
CurietemperatureinKelvin
•Astemperatureincreasesthemagnetismofaferromagneticmaterialdecreases.
•Therandomthermalmotiondestroystheorderingofspins.
•FortemperaturesabovetheCurietemperature,thelongrangeorderofspinis
lostandonlyashortrangeorderexists.

26. CURIE –WEISS LAW
•Curie-WeissLawLimitation;
oTheCurie-Weisslawholdsfalseinmany
materials.
oInstead,thereisacriticalbehavioroftheform.χ
∼
1
(??????−??????
??????)γ
oAttemperatureT≫Tc,theexpressionofthelaw
stillholdstrue.But,????????????willbereplacedby
temperature(θ)higherthantheCurie
temperature.

27. PROPERTIES AND APPLICATIONS OF IRON
PROPERTIES
•Pureironissoft,malleable,andductile
•Itrustsindampair,butnotindryair.
•Itdissolvesreadilyindiluteacids.
•Itmeltsat1536°Candboilsat2861°C.
•Beingametalitismagneticinnature.
•Ironisalustrous,ductile,malleable,silver-graymetal(groupVIIIofthe
periodictable).

28. PROPERTIES AND APPLICATIONS OF IRON
PROPERTIES
•Itisknowntoexistinfourdistinctcrystallineforms;
oOrdinaryorα-iron(alpha-iron)atlowertemperature
oγ-iron(gamma-iron)issoftinnature
oδ-iron(delta-iron)
oAtveryhighpressure,epsilon-ironexists(€-iron)
•Atroomtemperature,thismetalisintheformofferrite(α-iron)
•Theinternalarrangementoftheatomsinthecrystallatticechangesinthe
transitionfromoneformtoanother.
•Thetransitionfromα-irontoγ-ironoccursatabout910°C,andthetransition
fromγ-irontoδ-ironoccursatabout1400°C

29. PROPERTIES AND APPLICATIONS OF IRON
APPLICATIONS
•Ironisusedinnumeroussectorssuchaselectronics,manufacturing,
automotive,andconstructionandbuilding.
•Itisusedastheprimaryconstituentofferrousmetals/alloysandsteels
•Itisalloyedwithcarbon,nickel,chromiumandvariousotherelementsto
formcastironorsteelwhichisused;
oInfabricatedmetalproducts
oInindustrialmachinery
oIntransportationequipment
oIninstruments
oInmagnets

30. PROPERTIES AND APPLICATIONS OF IRON
APPLICATIONS
•Ironisusedtomakealloysteelslikecarbonsteelswithadditivessuchasnickel,
chromium,vanadium,tungstenandmanganese.
•Theseareusedtomakebridges,electricitypylons,bicyclechains,cuttingtools
andriflebarrels.
•Castironcontains3–5%carbon.Itisusedforpipes,valvesandpumpsandinthe
manufacturingof‘resistancegrids’tobeusedinthestartingoflargedcmotors
•IroncatalystsareusedintheHaberprocessforproducingammonia.
•Galvanizedsteelandironwireswhicharegenerallyusedforearthconductorin
lowvoltagedistributionsystemsmayalsobeusedforthephaseconductorin
ruralareas

31. ALLOYS OF IRON
•Alloyisthesubstance,whichiscomposedoftwoormoremetals.
•Thepropertiesofalloysaredifferentfromthoseoftheirconstituentelements.
Propertiessuchasstrengthandcorrosionresistancemaybeconsiderably
greaterforanalloythanforanyoftheseparatemetals.Hence,alloysare
moregenerallyusedthanpuremetals.
•Pureironhaslowresistivity,whichresultsinhighereddycurrentlosses.
Theselossescanbeminimizedbyincreasingtheresistivityofthematerial,
whichisachievedbyadding1-4%ofsilicontoiron.
•Themostimportantalloyofironissteel.Steelisstrongerandharderthan
wroughtiron(pureiron)
•Themixtures(alloys)ofsteelwithmetalslikechromium,manganese,
molybdenum,nickel,tungsten,andvanadium,arestrongerandharderthan
steelitself,andmanyofthemarealsomorecorrosion-resistantthanironor
steel.

32. ALLOYS OF IRON
•Carbonsteels
oSteelsinwhichthemainalloyingadditiveiscarbon.
oMildsteelisthemostcommonduetoitslowcost.
oItisneitherbrittlenorductile,hasrelativelylowtensilestrength,andis
malleable.
oSurfacehardnesscanbeincreasedthroughcarburizing.
oHighcarbonsteelshaveahighercarboncontentwhichprovidesamuch
higherstrengthatthecostofductility.
•Alloysteels
oSteels(ironandcarbon)alloyedwithothermetalstoimproveproperties.
oThemostcommonmetalsinlowalloyedsteelsaremolybdenum,chromium,
andnickeltoimproveweldability,formability,wearresistance,and
corrosionresistance.

33. ALLOYS OF IRON
•Stainlesssteels
oSteelsthatcontainaminimumof10%chromium.
oTherearemanygradesofstainlesssteel,butthemostcommongradeused
fortypicalcorrosionresistantapplicationsistype304,alsoknownas18-8.
oTheterm18-8referstotheamountofchromium(18%)andnickel(8%)
combinedwithironandotherelementsinsmallerquantities.
oThemetal’sfinishisdepictedbyanumber,3to8,with3beingtheroughest
and8beingamirror-likefinish.
oOtherspecificationsconsideredincludetexturesandcoatings.

34. ALLOYS OF IRON
•Toolsteels
oSteelsdesignedforbeingmadeintotools.
oTheyareknownfortoughness,resistancetoabrasion,abilitytoholda
cuttingedge,and/ortheirresistancetodeformationathightemperatures.
oThethreetypesoftoolsteelavailableare;
coldworksteelsusedinloweroperatingtemperatureenvironments,
hotworksteelsusedatelevatedtemperatures,and
highspeedsteelsabletowithstandevenhighertemperaturesgivingthem
theabilitytocutathigherspeeds.

35. ALLOYS OF IRON
•Castiron
oIronalloyderivedfrompigiron,alloyedwithcarbonandsilicon.
oCarbonisaddedtothebasemeltinamountsthatexceedthesolubilitylimits
inironandprecipitatesoutasgraphiteparticles.
oSiliconisaddedtothemelttonucleatethegraphitewhichoptimizesthe
propertiesofcastiron.
oItisreferredtoascheap,dirty,brittlemetal
oCastironisgettingmuchmoreattentionandusetodaybecauseofits
machinability,lightweight,strength,wearresistance,anddamping
properties.

36. ALLOYS OF IRON
•Maragingsteels
oCarbonfreeiron-nickelalloyswithadditionsofcobalt,molybdenum,
titanium,andaluminum.
oThetermmaragingisderivedfromthestrengtheningmechanism,whichis
transformingthealloytomartensitewithsubsequentagehardening.
oWithyieldstrengthsbetween1400and2400MPa,maragingsteelsbelongto
thecategoryofultra-high-strengthmaterials.
oThehighstrengthiscombinedwithexcellenttoughnesspropertiesand
weldability.

37. ALLOYS OF IRON
•Mu-metal
oItconsistsofiron,nickel,copperandchromium.
oItisasoftmagneticmaterialusedinminiaturetransformersforcircuit
applications
•Nickelironalloys
oGoodchoicefordeviceslikeaudiotransformerandrecordinghead.
oThesealloyshavehighhigherinitialpermeability,lowhysteresisandlow
eddycurrentlosses.
oCommercialnameofNickelironalloyis“hypenik”.
oTwoimportantcompositionsarethefollowing
1)50Permalloy–50%Ni50%Fe
2)78Permalloy–78%Ni22%Fe
3)Supermalloy-78%Ni17%Feand5%Mo

38. ALLOYS OF IRON
•Siliconironalloy:
oSiliconincreasestheelectricalresistivityofiron.
oItreduceshysteresisloss.
oThemagnetostrictioneffectisalsoreduced.
oItincreasesthepermeability
oSiliconironalloyisusedintheformofthinsheetscalledlaminations.These
laminationsareusedintransformers,smallmachinesandlargeturbo
generators.
oSiliconironalloywith2%siliconhaslargemagneticsaturation.Hence,itis
employedinthecoresofelectricalrotatingmachines.
oSilicon–ironalloywith4%siliconisusedinthemagneticcircuitsofpower
transformerswhichoperateunderveryhighfluxdensity.
oPermeabilityofsiliconironalloyisrelativelylowunderweakfields.
Thereforeitisnotsuitableforhighsensitivityapplicationssuchasin
communicationequipment.

39. HARD AND SOFT MAGNETIC MATERIALS

40. HARD AND SOFT MAGNETIC MATERIALS
SOFTMAGNETICMATERIALS
Properties:
•Thesemagneticmaterialscanbeeasilymagnetizedanddemagnetized,butthey
cannotbepermanentlymagnetized
•Lessenergyisrequiredtomagnetizeanddemagnetizeasoftmagneticmaterial.
•Theseareusedtomakeelectromagnets.
•Eg:Ironsiliconalloys,Ferrousnickelalloy,Iron-cobaltalloys,Ferriteand
garnets
•LowHysteresislossandlowcoercivity.
•Thesematerialshavelargevaluesofpermeabilityandsusceptibility

41. HARD AND SOFT MAGNETIC MATERIALS
SOFTMAGNETICMATERIALS
Applications:
•Softmagneticmaterialshaverelativelysmallandnarrowhysteresisloopand
hencesmallenergylosspercycleofmagnetization.Theyarewidelyusedforthe
constructionofcoresofelectricalrotatingmachines,transformers,andfor
makingelectro-magnets,reactors,relays
•Softmagneticmaterialsaremostlyusedwherechangingmagneticfluxis
associated,suchasmagneticcoreofelectricmotors,alternators,DCgenerators,
electricaltransformers,protectiverelays,inductors.
•Usedformakingapathforfluxinpermanentmagneticmotors
•Usedformagneticshielding,electromagneticpole-pieces,toactivatethe
solenoidswitch
•Permanentmagnetusessoftmagneticmaterialtomakeapathforfluxlines

42. HARD AND SOFT MAGNETIC MATERIALS
SOFTMAGNETICMATERIALS
Examples:
•NickelIronAlloys-Itisusedincommunicationequipmentsuchasaudio
transformer,recordingheadsandmagneticmodulators.Sinceithashighinitial
permeabilityinfeeblefields,lowhysteresisandloweddycurrentlosses.
•Grainorientedsheetsteel:usedtomaketransformercores.
•Mu-metal:usedinminiaturetransformersmeantforcircuitapplications.
•Ceramicmagnets:usedformakingmemorydevicesformicrowavedevicesand
computer

43. HARD AND SOFT MAGNETIC MATERIALS
HARDMAGNETICMATERIALS
Properties:
•Thesemagneticmaterialscannotbeeasilymagnetizedanddemagnetized,but
theycanbepermanentlymagnetized.
•Thereasonisthatthedomainwallsaremotionlessowingtocrystaldefectsand
imperfections.
•Hardmagneticmaterialshavelargehysteresislossduetolargehysteresisloop
area
•Theseareusedtomakepermanentmagnets.
•Highremnantmagnetization

44. HARD AND SOFT MAGNETIC MATERIALS
HARDMAGNETICMATERIALS
Properties:
•TheshapeofBHloopisnearlyrectangle.
•Smallinitialpermeability.
•Relativelylowpermeabilityandsusceptibility
•ThesematerialshavehighCoercivityandretentivity.Hence,cannotbeeasily
magnetizedanddemagnetized.
•Highmagnetizingforceisrequiredtoattainmagneticsaturation.
•Eg:Alnicoalloy,Coppernickelironalloy,Coppernickelcobaltalloy

45. HARD AND SOFT MAGNETIC MATERIALS
HARDMAGNETICMATERIALS
Applications:
•Hardmagneticmaterials(suchascarbonsteel,tungstensteel,cobaltsteel
andhardferrites)havelargehysteresisloopareaandconsequentlylarge
energylosspercycleofmagnetizationandareusedinmakingallkindsof
instrumentsanddevicesrequiringpermanentmagnets.
Variousotherapplicationsare;
•Automotive:motordrivesforfans,wipers,injectionpumps,startermotors,
Controlforseats,windowsetc.
•Telecommunication:Microphones,LoudSpeakers,TelephoneRingersetc.
•Dataprocessing:Printers,SteppingMotors,DiscDrivesandActuators.

46. HARD AND SOFT MAGNETIC MATERIALS
HARDMAGNETICMATERIALS
Applications:
•Consumerelectronics:Homecomputers,Clocks,DCMotorsforshowersetc.
•Electronicandinstrumentation:EnergyMeterDisc,Sensors,Dampersetc.
•Industrial:Liftingapparatus,Robotics,Metersetc.
•Astroandaerospace:Auto-compass,Couplings,Instrumentationetc.
•Biosurgical:NMR/MRIbodyscanner,WoundClosuresetc.

47. HARD AND SOFT MAGNETIC MATERIALS
HARDMAGNETICMATERIALS
Examples:
•Steel:
•Carbonsteelhavelargehysteresisloop.Itisusedinmakingmagnetsfor
toysandincertaintypesofmeasuringmeters.Duetoanyshockorvibration,
theylosetheirmagneticpropertiesrapidly.
•Tungstensteel,chromiumsteelandcobaltsteelhavehighenergyproduct.
•Alnico:Itismadeupofaluminium,nickelandcobalt.Alnico5isthemost
importantmaterialusedtocreatepermanentmagnet.Itisusedinhigh
temperatureoperation

48. HARD AND SOFT MAGNETIC MATERIALS
HARDMAGNETICMATERIALS
Examples:
•Rare-EarthAlloys:SmCo5,Sm2Co17,NdFeBetc.
•HardFerritesorCeramicmagnets(likeBariumFerrites):Thesematerialscanbe
powderedandusedasabinderinplastics.Theplasticsmadebythismethodare
calledplasticmagnet.
•BondedMagnets:ItisusedinDCmotors,Steppermotorsetc.
•Nanocrystallinehardmagnet(Nd-Fe-BAlloys):Thesmallsizeandweightof
thesematerialmakeitsuitableforuseinmedicaldevices,thinmotorsetc.

49. HARD AND SOFT MAGNETIC MATERIALS
COMPARISON

50. FERRITES
•Ferrites are compounds of iron oxides with oxides of other metal.
•A ferrite is a type of ceramic compound composed of iron(III) oxide (Fe2O3)
combined chemically with one or more additional metallic elements.
•They are both electrically nonconductive and ferrimagnetic, meaning they can
be magnetized or attracted to a magnet.
•Based on their magnetic coercivityand resistance to being demagnetized,
ferrites are of two types; soft and hard ferrites
•Hard ferrites have high coercivity, hence they are difficult to demagnetize. They
are used to make permanent magnets, for devices such as refrigerator magnets,
loudspeakers and small electric motors.

51. FERRITES
•Soft ferrites have low coercivity. They are used in the electronics industry
to make ferrite cores for inductors and transformers, and in various
microwave components.
•Ferrite compounds have extremely low cost, being made of iron oxide (i.e.
rusted iron), and also have excellent corrosion resistance.
•They are very stable and difficult to demagnetize, and can be made with
both high and low coercive forces.
•It is used for high frequency applications.

52. FERRITES
•Mechanically, they have pure iron character.
•They have low tensile strength and are brittle.
•Ferrites can also be used in the design of ferromagnetic amplifiers of microwave
signals.

53. FERRITES
Properties
•Hard
•Brittle
•Iron-containing
•Polycrystalline
•High electrical resistivity
•Low electrical losses
•Significant saturation magnetization
•Very good chemical stability
•Generally grey or black

54. FERRITES
CLASSIFICATION:
Soft ferrites
•Softferritedoesnotretainsignificantmagnetization.
•Theyhavealowcoercivity
•Usedintransformersorelectromagneticcoresandcontainnickel,zinc,or
manganesecompounds.
•Manganese-zincferrites(MnZn)havehigherpermeabilityandsaturation.
•Nickel-zincferrites(NiZn)exhibithigherresistivitythanMnZn,andare
thereforemoresuitableforfrequenciesabove1MHz.

55. FERRITES
CLASSIFICATION:
Hard ferrites
•Inhardferrites,magnetizationisconsideredpermanent.
•Havehighcoercivity.
•Ironoxideandbariumorstrontiumcarbonateareusedinmanufacturingofhard
ferritemagnets
•Strontiumferrite,SrFe12O19(SrO·6Fe2O3),usedinsmallelectricmotors,
micro-wavedevices,recordingmedia,magneto-opticmedia,telecommunication
andelectronicindustry.
•Bariumferrites,BaFe12O19(BaO·6Fe2O3),arerobustceramicsthatare
generallystabletomoistureandcorrosion-resistant.Theyareusedin
loudspeakermagnetsandasamediumformagneticrecording,e.g.onmagnetic
stripecards.
•Cobaltferrite,CoFe2O4(CoO·Fe2O3),usedinsomemediaformagnetic
recording

56. CHARACTERISTICS :
FERRITES

57. FERRITES
APPLICATIONS
•Ferriteshaveimportanceinengineeringandtechnologysincetheypossess
spontaneousmagneticmomentbelowtheCurietemperaturejustasiron,cobalt,
nickel.
•Duetoveyloweddycurrentlosses,ferritesareusedasacoreofcoilsin
microwavefrequency(highfrequency)devicesandcomputermemorycore
elements.
•Duetorelativelylowpermeabilityandfluxdensitycomparedtoiron,ferrites
arenotsuitablefortheuseinhighfieldandhighpowerapplications,suchas
motors,generatorsandpowertransformers,buttheycanbeusedinlowfield
andlowpowerapplications.

58. FERRITES
APPLICATIONS
•Ferritesareusedasferromagneticinsulatorsinelectricalcircuits.
•FerriteslikeZnOfindlowfrequencyapplicationsintimers.Theyarealso
usedasswitchesinrefrigerators,airconditioners,etc.
•Ferritesareusedasmagneticheadtransducerinrecording.
•Power transformer and chokes: HF Power supplies and lighting ballasts
•Inductors and tuned transformers: Frequency selective circuits
•Pulse and wideband transformers: Matching devices
•Magnetic deflection structures: TV sets and monitors

59. FERRITES
APPLICATIONS
•Recording heads: Storage devices
•Rotating transformers: VCR’s
•Shield beads and chokes: Interference suppression
•Transducers: Vending machines and ultrasonic cleaners
•Catalysis: high surface area, controlled crystal surfaces
•Optical properties: sun screen, hyper thermic cancer treatment, Fluorescent tags
•Light scattering: smoke/fog screens

60. MAGNETIC MATERIALS USED IN RELAYS
oA relay is an electrically operated switch.
oA simple electromagnetic relay consists of a coil of wire surrounding a soft
iron core, an iron yoke which provides a low reluctance path for magnetic flux,
a movable iron armature and one or more set of contacts.
oWhen an electric current is passed through the coil, it generates a magnetic
field, that attracts the armature and movement of the movable contact either
makes or breaks a connection.

61. MAGNETIC MATERIALS USED IN RELAYS
Themagneticmaterialsusedinrelaysare:
•CeramicMagnets:
oCeramicmagnetsarecomposedofStrontiumorBariumFerriteanda
ceramicbasematerial.
oCeramicmagnetsarehardandbrittle.
oAdvantages;1)Theyaretheleastexpensivemagnets.2)Theyarevery
resistanttocorrosion.3)Theyarestableuptoapproximately300°C.
•AlnicoTypes:
oAlnicomagnetsaremadeofalloysofAluminum,NickelandCobalt.
oInexpensive.
oTheyarestableuptoveryhightemperatures(550°C).
oTheyareveryresistanttocorrosion.

62. MAGNETIC MATERIALS USED IN RELAYS
•Samarium-Cobaltfamily
oTherearetwocompositionsofSamarium-Cobaltmagnets.Theyare
Sm1Co5andSm2Co17.
oTheexcellenttemperaturestabilitycanbeincreasedbydopingGadolinium.
oThesearestableathightemperatures
oButtheyareexpensive

63. MAGNETIC MATERIALS USED ELECTRICAL MACHINES
•Iron-siliconalloymaterialcalledsiliconsteeldevelopedforrelativelystrong
alternatingmagneticfieldsaregenerallyusedintransformers,electricalrotating
machines,reactors,electromagnetsandrelays.
•Siliconsharplyincreasestheelectricalresistivityofiron,thusdecreasingthe
ironlossesduetoeddycurrents.
•Itincreasesthepermeabilityatlowandmoderatefluxdensitiesbutdecreasesit
athighdensities.
•Additionofsilicontoironreducesthehysteresisloss.
•Themagnetostrictioneffectisalsoreduced

64. MAGNETIC MATERIALS USED ELECTRICAL MACHINES
•Inthepast,ironusedasthecorematerialintheformofsheetscausedgradual
deteriorationofthematerialduetorepeatedheatingandcooling.Thisdifficulty
wasovercomebyusingsiliconsheetsteelascorematerial.
•Highfrequencypowertransformersoperatingat10to100kHz,pulse
transformersupto100’MHz,recordingheads,etc..makeuseofcoresmadeof
softferrites.
•Alnicomagnetsfindapplicationsinmicrowavedevices,motors,generators,
vendingmachinesandcommunicationdevices