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Magnetic forces, Materials and Devices

MR. HIMANSHU DIWAKAR

ASSISTANT PROFESSOR

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2Magnetic Field

The region around a magnet in which it exerts forces on other magnets and on objects made of iron is a magnetic field.

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3Magnet Field: CauseMoving charges produce magnetic fields.

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4Magnetic Intensity OR Magnetising force (H)

Magnetic Intensity at a point is the force experienced by a north pole of unit pole strength placed at that point due to pole strength of the given magnet.

Its SI unit is ampere-turns per linear metre.

Magnetic Field Strength or Magnetic Induction or Magnetic Flux Density (B)

Magnetic Flux Density is the number of magnetic lines of force passing normally through a unit area of a substance.

Its SI unit is weber-m-2 or Tesla (T).

Relation Between B & H

B = μ H

(where μ is the permeability of the medium)

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5Magnetic Susceptibility (Xm )

It is the property of the substance which shows how easily a substance can be magnetised.

It can also be defined as the ratio of intensity of magnetisation (I) in a substance to the magnetic intensity (H) applied to the substance.

Xm = I / Hi) Susceptibility has no unit.ii) When –ve , solid is dimagnetic.iii) When small range of +ve, Solid is paramagnetic.iv) If large range value of +ve, Solid is ferromagnetic.v) It may be positive or negative.

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6Curie Temperature (C)The temperature above which ferromagnetic material looses their magnetic properties.

Above C temp, domain structure for gets destructed and domain looses their alignment.

Relation between Magnetic Permeability (μr) & Susceptibility (cm )

μr = 1 + cm

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7 Magnetic Dipole & Dipole Moment

A pair of magnetic poles of equal and opposite strengths separated by a finite distance is called a magnetic dipole.

The magnetic dipole moment is the product of the pole strength m and the separation 2l between the poles.

SI unit of pole strength is A.m .

Magnetic Dipole Moment is M = m.2l

The direction of the dipole moment is from South pole to North Pole along the axis of the magnet.

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The Phenomenon of attracting magnetic substances like iron, nickel, cobalt, etc.• A body possessing the property of magnetism is called a magnet.• A magnetic pole is a point near the end of the magnet where magnetism is concentrated.• Earth is a natural magnet.•The region where the magnetic forces act is called the “magnetic field”.

MagnetismJETGI

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Magnetism arises from the Magnetic

Moment or Magnetic dipole of Magnetic Materials.

When the electrons revolves around the nucleus Orbital magnetic moment arises, similarly when the electron spins, spin Magnetic moment arises.

The permanent Magnetic Moments can arise due to the 1.The orbital magnetic moment of the electrons2.The spin magnetic moment of the electrons, and 3.The spin magnetic moment of the nucleus.

Origin Of MagnetisationJETGI

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05/03/2023

ORIGIN OF MAGNETISM IN MATERIALS

Nuclear spin

Orbital motion of electrons

Origin of Magnetism Spin of electrons

A moving electric charge, macroscopically or “microscopically” is responsible for Magnetism.

Weak effect

Unpaired electrons required for net Magnetic Moment

Magnetic Moment resultant from the spin of a single unpaired electron→ Bohr Magneton = 9.273 x 1024 A/m2

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• Magnetic Materials are those materials in which a state of magnetization can be induced.

• Such materials when magnetized create a magnetic field in the surrounding space.

Magnetic Materials JETGI

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• Paramagnetic• Diamagnetic• Ferromagnetic• Ferrimagnetic• Antiferromagnetic

Classification Of Magnetic Materials JETGI

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• It is a substance or body which very weakly attracted by the poles of a magnet, but not retaining any permanent magnetism.

• These have relative permeability slightly greater than unity and are magnetized slightly.

• They attract the lines of forces weakly.

Paramagnetic JETGI

14• Al, Pt, Ca, O2 are such materials. JETGI

15ParamagnetismJETGI

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• It is a substance which create a magnetic field in opposite to an externally applied field.

• Susceptibility is negative.

• These have relative permeability slightly less than unity.

• They repel the lines of force slightly.

Diamagnetic JETGI

17• The examples are bismuth silver, copper and hydrogen. JETGI

18DiamagnetismJETGI

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• A type of material that is highly attracted to magnets and can become permanently magnetized is called as ferromagnetic.

• The relative permeability is much greater than unity and are dependent on the field strength.

• These have high susceptibility.

Ferromagnetic JETGI

20• Fe, Co, Ni, Cr, Mn are such materials.

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21 Ferrimagnetism 1.)Ferrimagnetism is a phenomenon in which the magnetic interaction between

any two dipoles align anti-parallel to each other.

2.)But since the magnitude of dipoles are not equal.

3.)The cancellation of magnetic moments become incomplete resulting in a net magnetization in the material.

4.)Ferrimagnetic materials possess magnetic dipoles moment due to the spin of the electron.

5.)A Ferrimagnetic material is composed of more state of different transition elements.

6.)The susceptibility is very Large and +ve.

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22 Antiferromagnetism

It is refer to a phenomenon in which the magnetic interaction between any two dipoles align themselves anti-parallel to each other.

Since all dipoles are of equal magnitude,the net magnetisation is zero.

Like ferromagnetic materials antiferromagnetic materials also possess dipole moment due to spin of the electron.

The opposite alignment of adjacent dipoles due to an exchange interaction.

The susceptibility is very small and is +ve.

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23AntiferromagnetismJETGI

24Type of Magnetism Susceptibility Atomic / Magnetic Behaviour Example /

Susceptibility

Diamagnetism Small & negative. Atoms have no magnetic moment

Au Cu

-2.74x10-6-0.77x10-6

Paramagnetism Small & positive.

Atoms have randomly oriented magnetic moments

β Pt Mn

0.19x10-6 21.04x10-6 66.10x10-6

Ferromagnetism

Large & positive, function of applied field, microstructure dependent.

Atoms have parallel aligned magnetic moments

Fe ~100,000

Antiferromagnetism Small & positive.

Atoms have mixed parallel and anti-parallel aligned magnetic moments

Cr 3.6x10-6

Ferrimagnetism

Large & positive, function of applied field, microstructure dependent

Atoms have anti-parallel aligned magnetic moments

Ba ferrite

~3

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Magnetization In Materials

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26Introduction

Magnetism arises from the Magnetic Moment or Magnetic dipole of Magnetic Materials.

When the electrons revolves around the nucleus Orbital magnetic moment arises, similarly when the electron spins, spin Magnetic moment arises.

The permanent Magnetic Moments can arise due to the 1.The orbital magnetic moment of the electrons2.The spin magnetic moment of the electrons, and 3.The spin magnetic moment of the nucleus.

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27Magnetic Induction or Magnetic flux Density

The Magnetic induction in any material is the number of lines of magnetic force passing through unit area perpendicularly. Units: Wb/m2 or Tesla.

Magnetic field intensity (H)

The Magnetic field intensity at any point in the magnetic field is the force experienced by an unit north pole placed at that point. Units : A/m

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28Permeability: ( µ )

The Magnetic induction B is proportional to the applied Magnetic field intensity H.

HBHB

HB

Where µ permeability of a medium

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29Relative permeability µr

The ratio of permeability of medium to the permeability of free space is called relative permeability µr of the solid.

00

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BB

HBHB

r

r

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30MagnetizationMagnetization refers to the

process of converting a non-magnetic material into a Magnetic material.

The intensity of Magnetization is directly related to the applied field H.

HM

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32Origin of Magnetic MomentThe Magnetic moment in a material originates from the orbital motion and spinning motion of electrons in an atom.

eµlm

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33Consider an atom & each electron in that, orbiting around the nucleus produces a loop current i = q / ti = q f Where f is a frequency of electron..If L is the angular momentum of electron, the Magnetic moment of the electron

µlm = (Area of loop) x (Current)

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Thank you