magnetic materials.ppt

lecture note

1. MAGNETIC
MATERIALS

2. MAGNETIC MATERIALS –Introduction
MAGNETIC
MATERIALS

3. MAGNETIC MATERIALS
•THE MATERIALS WHICH GET
EASILYMAGNETIZED IN A MAGNETIC
FIELD.

4. MAGNET:ADEVICETHATATTRACTSIRON
ANDPRODUCESAMAGNETICFIELD
MANY OF OUR MODERN
TECHNOLOGICAL DEVICESRELAY
ONMAGNETISM ANDMAGNETIC
MATERIALS
POWER GENERATORS, TRANSFORMERS,
ELECTRIC MOTORS, RADIO,TELEVISION,
TELEPHONES,COMPUTERS&COMPONENTS OF
SOUND&VIDEOREPRODUCTIONSYSTEMS.

5. i.e.H=
B
amperem
1 Magneticdipole:Thetwoequalandopposite
magneticpolesareseparatedbyasmalldistance.
Magneticdipolemoment:Productofpole
strengthandlengthofthemagnet.m = ml
MagneticInduction(or)magneticfluxdensity(B):It
representsthemagnitudeoftheinternalfieldstrength
withinasubstancethatissubjectedtoanHfield.
MagneticfieldIntensity(H):
Ratiobetweenthemagneticinduction
andthepermeabilityofthemedium

6. Magnetic Permeability (µ):
Ratio of the magnetic induction to the
applied magnetic field intensity
MagneticSusceptibility(χ):Ratiobetweenthe
intensityofmagnetizationtotheapplied
magneticfieldintensity
Intensity of Magnetization(I or M):
•The process of converting a non magnetic
material into a magnetic material.
•Magnetic moment per unit volume.. Unit-A/m=
B
H
henrym
1 =
I
H

7. Relationbetweenµ&χ:B=H B=
0( )IH +
The relative permeability
orr=
0
orr=
B
0
H
Substituting the B value, we get,r=
0
( )IH +
0H =
I
H
1 + r=1 +

8. CLASSIFICATION OF MAGNETIC MATERIALS
Classifiedintotwocategories,
1.Withoutpermanentmagneticmoments:
i)Diamagneticmaterials
2.Withpermanentmagneticmoments:
i)Paramagneticmaterials
ii)Ferromagneticmaterials
iii)Anti-Ferromagneticmaterials
iv)Ferrimagneticmaterials

9. An Introduction
MAGNETIC MATERIALS –Ferro magnetism
GenerallyMagnetFerroMagneticmaterial
Abilitytopickupthemateriallikeiron
Itispermanentmagneteveninnofield.
Itexhibitsamagneticmomentintheabsenceofthefield.

10. Explanation
MAGNETIC MATERIALS –Ferro magnetism
Netintrinsicmagneticdipolemoment–
duetospinofe
-n
Theneighbordipoleshavingstrong
interactioneveninnofield-SPIN
EXCHANGEINTERACTION
Exchangeinteractionalignsparallel
andspreadsoverasmallfinitevolume
iscalleddomain
Allmomentswithinthedomainisin
samedirection
Moredomains

11. Properties
MAGNETIC MATERIALS –Ferro magnetism
Havingspontaneousmagnetizationanddomainstructure
stronglymagnetizedinthedirectionoftheexternalfield
Ifitissuspendedfreely,itsetitselfparalleltotheexternal
field.
exhibithysteresisandrelativepermeabilityislarge.
Thevaluemagneticsusceptibilityislarge&dependsonT
Abovecertaintemperature,theferromagneticmaterial
becomesparamagneticmaterial.ThistemperatureiscalledCurie
temperature.
Showsmagnetostrictioneffect.

12. MAGNETIC MATERIALS –Ferro magnetism
Permanent&largemagnetizationsdueto
parallelalignmentofneighboringmagnetic
moments.
Magneticsusceptibilitiesishigh
WhenT<‘θ’thematerialisinferromagnetic
state
χisverylargeduetospontaneousmagnetization.
Duetolargeinternalfield,thedipolesarrangein
samedirection
Eachdomainisspontaneousmagnetizedevenno
appliedField
Spin Direction

13. Domain Theory of Ferromagnetism
MAGNETIC MATERIALS –Ferro magnetism
To Explain HYSTERESIS effect, Weiss proposed
the concept of domains in 1907.
Size 10
-6
m
Itconsistsofspontaneouslymagnetizedsmall
regionswhereallthemagneticmomentsare
alignedinsamedirection.Thissmallregionare
calledasdomains.

14. Domain Theory of Ferromagnetism
MAGNETIC MATERIALS –Ferro magnetism
Absence of field, domains
oriented in diff. directions
But Magnetic Moments in same
Direction
Results magnetisation is zero
DOMAIN STRUCTURE
In the field, domains aligned in the direction of field
If the field is removed, the domains restores its original.
This cause the hysteresis.

15. MAGNETIZATION OF DOMAINS
MAGNETIC MATERIALS –Ferro magnetism
When External field is applied two possible alignment of
domain
By motion of domain walls By rotation of domains
•Themovementofdomainwalls–
inweakmagneticfields
•Magneticmomentincreases&
boundary ofdomains are
displaced,volumeofdomains
changes
•If applied field is strong, the
domains can rotate into the
field direction.

16. INTERNAL ENERGY IN DOMAINS
MAGNETIC MATERIALS –Ferro magnetism
Its made up from the following contributions
Magneto static (or)
the exchange energy
Crystallineenergy(or)
theanisotropyenergy
Domain wall energy
(or) Bloch wall energy
Magnetostriction energy.

17. MAGNETIC MATERIALS –Ferro magnetism
Neighboringatomicmagneticdipolesare
interactingwithEachotherandalign
themselves.
Magnetostatic Energy or The Exchange Energy
Theinteractionenergybetweenthe
neighboringatomicmagneticdipolesis
calledexchangeenergyorthemagnetic
fieldenergy.

18. MAGNETIC MATERIALS –Ferro magnetism
Most of the crystals are Anisotropic.
(having a different value when measured in different
directions)
have easy and hard directions of
magnetization.
higher fields magnetised in hard
directions.
Theexcessofenergyrequiredtomagnetizeacrystalin
aparticulardirection,overthatrequiredtomagnetizeit
alongeasydirectioniscalledcrystallineenergyor
anisotropicenergy.
Crystalline Energy or The Anisotropic Energy

19. MAGNETIC MATERIALS –Ferro magnetism
Domain Wall Energy or Block Wall Energy
•The transition layer that separates adjacent
domains, magnetized in different directions
is called domain wall or block wall.
•The energy of domain wall is due to both
exchange energy and anisotropic energy.

20. MAGNETIC MATERIALS –Ferro magnetism
MagnetostrictionEnergy
Undermagneticfield,thedimensionswillchange.This
phenomenoniscalledmagnetostriction.
Ifthedomainsaremagnetisedindifferentdirectionstheywill
eitherexpandorcontract.
Thismeansthatworkmustbedoneagainsttheelastic
restoringforces.
Theworkdonebythemagneticfieldagainstthese
elasticrestoringforcesiscalledan
magnetostrictionenergyormagneticelastic
energy.