THE BASICS OF MAGNETISM - with the detailed explanation of magnetism and its related properties for a good seminar purpose

here is the detailed explanation of magnetism and its related properties for a good seminar purpose

1. THE BASICS OF MAGNETISM Comprehensive Overview of Magnetic Principles Presented by Kumaresh P Research Scholar SRM IST, VDP Campus, Chennai - 26 Date: 19.09.2025 19-09-2025 1

2. 19-09-2025 2 Historically the word ‘magnetism’ was derived from iron ore magnetite (Fe 3 O 4 ). In olden days, magnets were used as magnetic compass for navigation, magnetic therapy for treatment and also used in magic shows. In modern days, we use them in Motors, cycle dynamo, loudspeakers, magnetic tapes used in audio and video recording, mobile phones, head phones, CD, pen-drive, hard disc of laptop, refrigerator door, generator etc. MAGNETISM FROM THE MAGIC TO MODERN DAY

3. 19-09-2025 3 Earlier, both electricity and magnetism were thought to be two independent branches in physics. In 1820, H.C. Oersted observed the deflection of magnetic compass needle kept near a current carrying wire. This unified the two different branches, electricity and magnetism as a single subject ‘electromagnetism’ in physics. ACCIDENT TO ADVANCEMENT

4. 19-09-2025 4 MAGNETIC DIPOLE MOMENT (M d ) A system having two opposite magnetic poles separated by a distance   is called as a magnetic dipole. The magnetic dipole moment is defined as the product of its pole strength and magnetic length. where,  - magnetic pole strength  - length of the magnet A lso,   - electric current - area of cross section . 2. MAGNETIC FIELD (B) The magnetic field at a point is defined as a force experienced by the bar magnet of unit pole strength  

5. 19-09-2025 5 3. MAGNETIC FIELD LINES The imaginary representation of the magnetic field in a space are called magnetic field lines. 4. MAGNETIC FLUX ( Φ B ) The number of magnetic field lines crossing any area normally is defined as magnetic flux Φ B through the area. MAGNETISING FIELD: The magnetic field which is used to magnetize a sample or specimen is called the magnetising field. Magnetising field is a vector quantity and is denoted by and its unit is Am –1 .  

6. 19-09-2025 6 MAGNETIC PERMEABILITY: The magnetic permeability is the measure of ability of the material to allow the passage of magnetic field lines through it or the degree of penetration of magnetic field through the substance - absolute permeability - permeability of the medium - relative permeability     19-09-2025 6 Due to orbital motion, electron has magnetic moment and these magnetic moments orient randomly. Therefore, the net magnetic moment per unit volume of the material is zero . Under an external magnetic field, atomic dipoles are induced and they will try to align partially or fully along the direction of external field. The net magnetic moment per unit volume of the material is known as INTENSITY OF MAGNETIZATION.  

7. 19-09-2025 7 MAGNETIC SUSCEPTIBILITY: The ratio of the intensity of magnetization induced in the material to the magnetizing field  

8. 19-09-2025 8 19-09-2025 8 Permanent Magnetic Moment DIAMAGNETISM Long Range Order PARAMAGNETISM Nearest Neighbour Orientation FERROMAGNETISM Magnitude of Antiparallel moment ANTIFERRO MAGNETISM FERRIMAGNETISM NO YES NO YES PARALLEL ANTIPARALLEL EQUAL UNEQUAL MAGNETIC MATERIALS

9. 19-09-2025 9 FERROMAGNETIC MATERIALS 19-09-2025 9 I N THE ABSENCE OF EXTERNAL FIELD T he magnetic moments of electrons are parallel to each other and give rise to magnetic field. EFFECT OF MAGNETIC FIELD E ven if a small external magnetic field is applied, the magnetic moments which are already aligned parallel, reorient itself along the direction of the magnetic field and they become very strong magnets . T he number of unpaired electrons are more. Most of these spin magnetic moments point in one direction .

10. 19-09-2025 10 PROPERTIES Since some magnetisation is already existing in these materials, all the magnetic lines of force passes through it. They exhibit magnetisation even in the absence of external field. This property is called spontaneous magnetisation. Its susceptibility is positive and high and it is given by When the temperature is greater than curie temperature, ferromagnetic material becomes paramagnetic material. Permeability is very much greater than 1. Examples:  Ni, Co, Fe etc.

11. 19-09-2025 11 Ferromagnetic Domain Theory Introduction Ferromagnetism is explained by domain theory, first proposed by Weiss in 1907. Ferromagnetic materials are divided into small regions called  domains . 2. What are Domains? A domain is a region where all atomic magnetic moments (spins) are aligned in the same direction. Each domain acts like a tiny magnet with strong magnetization.

12. 19-09-2025 12 Random Orientation (No Field) Without an external magnetic field, domains are oriented randomly throughout the material. This cancels out their individual magnetic moments and results in zero net magnetization for the entire specimen. Alignment Under External Field When an external magnetic field is applied: Domains aligned with the field grow larger at the expense of others (domain wall motion). Other domains rotate their magnetization direction to align with the field (domain rotation). As more domains align, the overall magnetization increases and the specimen is magnetized. .

13. 19-09-2025 13 Permanent Magnets When the field is removed, some domains retain their alignment, causing the material to remain magnetized—this is called  magnetic remanence 19-09-2025 13 In short, Domain behavior in Unmagnetized state:  Domains point in random directions External field applied:  Domains align with field direction Domain walls:  Boundaries between differently oriented domains Saturation:  All domains aligned with external field Magnetic domains: Random alignment (left) vs. aligned under external field B₀ (right)

14. 19-09-2025 14 HYSTERESIS LOOP & MAGNETIC PROPERTIES KEY PROPERTIES: COERCIVITY ( H c ):  Magnetic field needed to reduce magnetization to zero RETENTIVITY (B r ):  Magnetization remaining when external field is removed SATURATION (B s ):  Maximum magnetization achieved HARD MATERIALS:  High coercivity, retain magnetization SOFT MATERIALS:  Low coercivity, easy to magnetize/demagnetize

15. 19-09-2025 15 APPLICATIONS OF MAGNETISM Electric Motors - Use electromagnetic induction to convert electrical energy to mechanical energy Generators - Convert mechanical energy to electrical energy using changing magnetic fields Transformers - Use magnetic cores to transfer energy between electrical circuits MRI Machines - Use strong magnetic fields (1.5-3 Tesla) to align protons for medical imaging Navigation - Compasses use Earth's magnetic field for navigation and direction finding Data Storage - Hard drives and magnetic tapes use magnetic materials for information storage

16. 19-09-2025 16 KEY TAKEAWAYS Magnetism  is a fundamental force involving magnetic fields and materials Five types  of magnetic behavior: diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic, ferrimagnetic Magnetic domains  explain how materials become magnetized Hysteresis loops  show magnetic memory and energy loss Applications  span from everyday items to advanced technology Modern materials  enable high-tech applications in energy and medicine

17. Thank you for your attention! Any questions? “Imagination is more important than knowledge.” – Einstein 19-09-2025 17