Magnetization - Magnetism and Matter

1. Magnetic Materials

• Diamagnetic Materials
  • Have a negative magnetic susceptibility and are weakly repelled by magnetic fields. (NCERT Class 12, Chapter 6, Page 133)
• Paramagnetic Materials
  • Have a positive magnetic susceptibility and are weakly attracted to magnetic fields. (NCERT Class 12, Chapter 6, Page 133)
• Ferromagnetic Materials
  • Have a strong positive magnetic susceptibility and are strongly attracted to magnetic fields. (NCERT Class 12, Chapter 6, Page 134)
• Antiferromagnetic Materials
  • Have a net magnetic moment of zero due to the cancellation of magnetic moments of adjacent atoms. (NCERT Class 12, Chapter 6, Page 138)
• Ferrimagnetic Materials
  • Have a net magnetic moment that is not zero but is less than the magnetic moment of the individual atoms due to the cancellation of magnetic moments of adjacent atoms. (NCERT Class 12, Chapter 6, Page 138)

2. Hysteresis Loop

• Explanation of Hysteresis Loop
  • A graphical representation of the relationship between the applied magnetic field and the magnetization of a material. (NCERT Class 12, Chapter 6, Page 135)
• Key Parameters
  • Saturation magnetization (Ms): The maximum magnetization that a material can achieve.
  • Retentivity (Mr): The magnetization that remains in a material after the applied magnetic field is removed.
  • Coercivity (Hc): The applied magnetic field required to reduce the magnetization of a material to zero. (NCERT Class 12, Chapter 6, Page 136)
• Comparison of Hysteresis Loops
  • Diamagnetic materials have a linear hysteresis loop.
  • Paramagnetic materials have a slightly curved hysteresis loop.
  • Ferromagnetic materials have a hysteresis loop with a significant curvature. (NCERT Class 12, Chapter 6, Page 136)

3. Ferromagnetism

• Microscopic Origin
  • Exchange interaction between electron spins is responsible for ferromagnetism. Parallel spins have lower energy than antiparallel spins. (NCERT Class 12, Chapter 6, Page 134)
• Domains and Domain Walls
  • Magnetic domains are regions within a ferromagnetic material where the magnetic moments of the atoms are aligned.
  • Domain walls are the boundaries between magnetic domains. (NCERT Class 12, Chapter 6, Page 134)
• Domain Wall Motion and Hysteresis
  • The movement of domain walls under the influence of an external magnetic field results in magnetization and hysteresis. (NCERT Class 12, Chapter 6, Page 136)

4. Magnetic Domains and Domain Walls

• Explanation
  • Magnetic domains are regions within a ferromagnetic material where the magnetic moments of the atoms are aligned.
  • Domain walls are the boundaries between magnetic domains. (NCERT Class 12, Chapter 6, Page 134)
• Factors Affecting Size and Shape of Domains
  • The size and shape of magnetic domains are affected by factors such as the strength of the exchange interaction, the anisotropy of the material, and the presence of defects. (NCERT Class 12, Chapter 6, Page 135)
• Influence of External Magnetic Fields
  • External magnetic fields can cause the alignment of magnetic domains and the movement of domain walls, resulting in changes in magnetization. (NCERT Class 12, Chapter 6, Page 136)

5. Soft and Hard Magnetic Materials

• Differences
  • Soft magnetic materials have a low coercivity and are easily magnetized and demagnetized.
  • Hard magnetic materials have a high coercivity and are difficult to magnetize and demagnetize. (NCERT Class 12, Chapter 6, Page 137)
• Applications
  • Soft magnetic materials are used in transformers, generators, and motors.
  • Hard magnetic materials are used in permanent magnets, magnetic recording media, and magnetic sensors. (NCERT Class 12, Chapter 6, Page 137)

6. Magnetic Properties of Matter

• Quantum Mechanical Explanation
  • Magnetism arises due to the spin of electrons. Electrons with unpaired spins contribute to the magnetic moment of an atom or molecule. (NCERT Class 11, Chapter 12, Page 271)
• Relationship between Electronic Structure and Magnetic Properties
  • The magnetic properties of a material depend on the number of unpaired electrons in its atoms or molecules. (NCERT Class 12, Chapter 6, Page 133)
• Magnetic Moments
  • Magnetic moment is a measure of the strength of a magnetic dipole.
  • The magnetic moment of an atom or molecule is determined by the number and arrangement of unpaired electrons. (NCERT Class 11, Chapter 12, Page 271)

7. Magnetic Circuits

• Basic Concepts
  • Magnetomotive force (MMF): The driving force that causes magnetic flux to flow in a magnetic circuit.
  • Reluctance: The opposition to the flow of magnetic flux in a magnetic circuit.
  • Flux density: The amount of magnetic flux per unit area. (NCERT Class 12, Chapter 6, Page 138)
• Magnetic Fields and Flux Density
  • The magnetic field intensity (H) is related to the MMF and the reluctance of the magnetic circuit.
  • The flux density (B) is related to the magnetic field intensity and the permeability of the material. (NCERT Class 12, Chapter 6, Page 138)
• Applications
  • Magnetic circuits are used in transformers, inductors, motors, and generators. (NCERT Class 12, Chapter 6, Page 139)

8. Superconductivity

• Introduction
  • Superconductivity is the phenomenon of zero electrical resistance and perfect diamagnetism in certain materials at very low temperatures. (NCERT Class 12, Chapter 6, Page 140)
• Meissner Effect
  • The expulsion of magnetic fields from a superconductor is known as the Meissner effect. (NCERT Class 12, Chapter 6, Page 140)
• Type I and Type II Superconductors
  • Type I superconductors exhibit perfect diamagnetism and a sharp transition to the superconducting state.
  • Type II superconductors exhibit paramagnetism and a more gradual transition to the superconducting state. (NCERT Class 12, Chapter 6, Page 141)

9. Critical Magnetic Field

• Explanation
  • The critical magnetic field (Hc) is the maximum magnetic field that can be applied to a superconductor without destroying its superconductivity. (NCERT Class 12, Chapter 6, Page 141)
• Variation with Temperature
  • The critical magnetic field decreases with increasing temperature. (NCERT Class 12, Chapter 6, Page 141)
• Applications
  • Superconductivity has applications in high-field magnets, energy-efficient devices, and medical imaging. (NCERT Class 12, Chapter 6, Page 142)