1 APPLIED PHYSICS CODE : 07A1BS05 CODE : 07A1BS05 I B.TECH I B.TECH CSE, IT, ECE & EEE CSE, IT, ECE & EEE UNIT-4 UNIT-4 CHAPTER : 2 CHAPTER : 2 NO. OF SLIDES : 24 NO. OF SLIDES : 24

2 S.No.ModuleLectureNo. PPT Slide No. 1IntroductionL Magnetic permeability, Magnetization L Origin of magnetic moment. L Classification of magnetic materials. Classification of magnetic materials. L UNIT INDEX UNIT-I

3 5 Hysteresis curve, Hysteresis curve, L Soft & Hard Magnetic Materials Soft & Hard Magnetic MaterialsL1424

4 Introduction Magnetic materials play a prominent role in modern technology. Magnetic materials play a prominent role in modern technology. They are widely used in industrial electronics and computer industry. They are widely used in industrial electronics and computer industry. The traditional methods of information storage and retrieval are rapidly replaced by magnetic storage. The traditional methods of information storage and retrieval are rapidly replaced by magnetic storage. Lecture-9

5 The magnetism of materials is mainly a consequence of interactions of uncompensated magnetic moments of constituent atoms and molecules. The magnetism of materials is mainly a consequence of interactions of uncompensated magnetic moments of constituent atoms and molecules. Basing on the response of materials in external magnetic field, and on the alignment of magnetic moments in the materials, they are classified into five types. Basing on the response of materials in external magnetic field, and on the alignment of magnetic moments in the materials, they are classified into five types.

6 Magnetic Polestrength Magnetic poles always occurs in pairs. Magnetic poles always occurs in pairs. Magnetic Polestrength (m) : It is scalar quantity Magnetic Polestrength (m) : It is scalar quantity.It is independent of the shape of the magnet..It is independent of the shape of the magnet..It depends on the state of magnetisation..It depends on the state of magnetisation. SI unit is – Am. SI unit is – Am.

7 Magnetic field strength(B) Magnetic field : The space around a magnet where its influence is felt is called magnetic field. Magnetic field : The space around a magnet where its influence is felt is called magnetic field. Magnetic induction field strength (B): Magnetic induction at a point is the force experienced by a unit north pole at that point. Magnetic induction field strength (B): Magnetic induction at a point is the force experienced by a unit north pole at that point. B is a vector. B is a vector. SI units of B : N/A.m (or) weber/m SI units of B : N/A.m (or) weber/m

8 Intensity of magnetic field (H) It is defined as the field that induces magnetism in a magnetic material. It is defined as the field that induces magnetism in a magnetic material. H is measured in Ampere/metre H is measured in Ampere/metre When a medium is exposed to magnetic field of intensity H it causes an induction B in the medium. When a medium is exposed to magnetic field of intensity H it causes an induction B in the medium.

9 Magnetic flux(Φ). Magnetic flux(Φ): It is the total number of lines of induction passing normal to the cross section. Magnetic flux(Φ): It is the total number of lines of induction passing normal to the cross section. S I unit : weber. S I unit : weber. Magnetic flux (Φ) Magnetic flux (Φ) : Φ is a scalar. : Φ is a scalar.

10 Magnetic permeability. Magnetic permeability: It is defined as the ability of a medium to allow the magnetic lines of force to pass through it. Magnetic permeability: It is defined as the ability of a medium to allow the magnetic lines of force to pass through it. B = μo (H+M) = μo (H + χ m H) B = μo (H+M) = μo (H + χ m H) B =μo μr H. B =μo μr H. Where μ r =1+χm. Which is called relative permeability. Where μ r =1+χm. Which is called relative permeability. Lecture-10

11 Intensity of magnetisation. Intensity of magnetization : It is the magnetic moment per unit volume or pole strength per unit area. Intensity of magnetization : It is the magnetic moment per unit volume or pole strength per unit area. I=M/V = (2l.m)/(2l.a) I=M/V = (2l.m)/(2l.a) a= area of crossection. a= area of crossection. It is measured in ampere/metre. It is measured in ampere/metre.

12 Magnetic moment It is a product of Magnetic length and pole strength of a magnet. It is a product of Magnetic length and pole strength of a magnet. Magnetic moment M=2l.m S.I unit of Magnetic moment is =Am 2. S.I unit of Magnetic moment is =Am 2. (or) N-m 3 /wb. (or) N-m 3 /wb. Lecture-11

13 Magnetic susceptibility. Magnetic susceptibility is defined as the ratio of intensity of magnetization (I) to intensity of magnetizing field. Magnetic susceptibility is defined as the ratio of intensity of magnetization (I) to intensity of magnetizing field. Magnetic susceptibility(χ): Magnetic susceptibility(χ): χ = I/H. χ = I/H. χ has no units. χ has no units.

14 Relative permeability. Relative permeability of material is expressed as the ratio of permeability of the material to the permeability of free space. Relative permeability of material is expressed as the ratio of permeability of the material to the permeability of free space. Thus μ r =μ/μ o. Thus μ r =μ/μ o. (or) (or) μ=μ r μ o. μ=μ r μ o.

15 Magnetic materials Magnetic materials Lecture-12 These are the substances, which upon which being introduced into the external magnetic field, change so that they themselves become sources of an additional magnetic field. These are the substances, which upon which being introduced into the external magnetic field, change so that they themselves become sources of an additional magnetic field. And they are classified into 5 groups. And they are classified into 5 groups. 1Diamagnetic. 4.Antiferromagnetic 2.Paramagnetic. 5.Ferrimagnetic 3.Ferromagnetic.

16 Diamagnetic materials The materials which when placed in magnetic field acquire feeble magnetism in the direction opposite to that of field are known as Diamagnetic substances. The materials which when placed in magnetic field acquire feeble magnetism in the direction opposite to that of field are known as Diamagnetic substances. Diamagnetic materials exhibit negative magnetic susceptibility. Diamagnetic materials exhibit negative magnetic susceptibility. The magnetization in diamagnetic materials is directed in opposite direction of the field applied. The magnetization in diamagnetic materials is directed in opposite direction of the field applied.

17 The relative permeability of a diamagnetic substance is slightly less than unity. The relative permeability of a diamagnetic substance is slightly less than unity. μ r < 1; which implies that substances are repelled by a magnetic field. μ r < 1; which implies that substances are repelled by a magnetic field. The magnetic susceptibility of diamagnetic materials is practically independent of temperature. The magnetic susceptibility of diamagnetic materials is practically independent of temperature. Examples: Hydrogen, air, water, gold silver. Examples: Hydrogen, air, water, gold silver.

18 Paramagnetic materials These are the substances which when placed in magnetic field acquire feeble magnetism in the direction of magnetic field. These are the substances which when placed in magnetic field acquire feeble magnetism in the direction of magnetic field. Examples: copper chloride, chromium, platinum. Examples: copper chloride, chromium, platinum. The magnetic susceptibility of paramagnetic substances is positive as the magnetization coincides the magnetic field. The magnetic susceptibility of paramagnetic substances is positive as the magnetization coincides the magnetic field.

19 Ferromagnetic materials Large magnetization occurs in thedirection of the field. Large magnetization occurs in thedirection of the field. The relative permeability is very high (several thousands). The relative permeability is very high (several thousands). When placed in magnetic field, it attracts the magnetic lines of force very strongly. When placed in magnetic field, it attracts the magnetic lines of force very strongly. Permanent and electromagnets are made using ferromagnetic materials. Permanent and electromagnets are made using ferromagnetic materials. Examples:ZnFe 2 O 4, CuFe 2 O 4, Zn-CuFeO 4 & FeO 4 etc. Examples:ZnFe 2 O 4, CuFe 2 O 4, Zn-CuFeO 4 & FeO 4 etc.

20 Antiferromagnetic materials Antiferromagnetic materials They show very little external magnetism. They show very little external magnetism. Magnetic susceptebility is positive and small. Magnetic susceptebility is positive and small. The magnetic dipole moments of adjacent atoms are antiparallel. The magnetic dipole moments of adjacent atoms are antiparallel.

21 Due to antiparallel magnetic dipole moments, the magnetic effect of antiferro magnetic material is zero, but possess magnetism due to temperature dependent disruption of the magnetic moment alignment. Due to antiparallel magnetic dipole moments, the magnetic effect of antiferro magnetic material is zero, but possess magnetism due to temperature dependent disruption of the magnetic moment alignment. The susceptibility increases with temperature upto T N (Neil temperature). Above Neil temperature, susceptibility decreases with increasing temperature. The susceptibility increases with temperature upto T N (Neil temperature). Above Neil temperature, susceptibility decreases with increasing temperature.

22 Ferrimagnetic materials Magnetic dipole moments of adjacent moloecules or atoms are antiparallel and unequal in magnitude. It results in a net magnetisation in the material. Magnetic dipole moments of adjacent moloecules or atoms are antiparallel and unequal in magnitude. It results in a net magnetisation in the material. Magnetic susceptibility is large and positive. Magnetic susceptibility is large and positive. Above Curie temperature, thermal dnergy randimizes the individual magnetic moments and the material becomes paramagnetic. Above Curie temperature, thermal dnergy randimizes the individual magnetic moments and the material becomes paramagnetic. Examples: copper, zinc, cadmium, iron, cobalt, nickel, etc. Examples: copper, zinc, cadmium, iron, cobalt, nickel, etc.

23 Hysteresis Hysteresis Lecture-13 When a magnetic field is applied on a ferromagnetic material then magnetization takes place. This magnetizatio9n always lags behind the applied magnetic field. This phenomenon is known as hysteresis of a ferromagnetic material. When a magnetic field is applied on a ferromagnetic material then magnetization takes place. This magnetizatio9n always lags behind the applied magnetic field. This phenomenon is known as hysteresis of a ferromagnetic material.

24 Magnetic materials are classified into soft materials and hard materials. Magnetic materials are classified into soft materials and hard materials. Lecture-14 Soft magnetic materials are easily magnetised and demagnetised, and therefore used in ac applications. Soft magnetic materials are easily magnetised and demagnetised, and therefore used in ac applications. Hard magnetic materials retain magnetism on a permanent basis, and are used in producing permanent magnets. These materials play an important role in information storage devices.