MP Board · Class 12 · Physics · Magnetism and MatterDifferentiate between Diamagnetic, Paramagnetic, and Ferromagnetic substances on the basis of their magnetic properties, susceptibility, and behavior in a non-uniform magnetic field.

Introduction to Magnetic Materials\nSubstances are classified into different categories based on their response to an external magnetic field and their atomic or molecular magnetic structures. The primary magnetic classifications are diamagnetic, paramagnetic, and ferromagnetic substances.

1. Diamagnetic Substances

• Behavior in Magnetic Field: Diamagnetic substances are weakly repelled by a magnet. When placed in a non-uniform magnetic field, they tend to move from stronger parts of the field to weaker parts.
• Magnetic Susceptibility ($\chi$): They possess a small and negative magnetic susceptibility ($\chi < 0$).
• Relative Permeability ($\mu_r$): Their relative permeability is slightly less than unity ($\mu_r < 1$).
• Effect of Temperature: The magnetic susceptibility of diamagnetic substances is independent of temperature (except for certain metals like bismuth).
• Origin: This property arises due to orbital motion of electrons creating induced magnetic moments that oppose the external field (Lenz's law at atomic scale).
• Examples: Bismuth, copper, water, gold, bismuth, and nitrogen.

2. Paramagnetic Substances

• Behavior in Magnetic Field: Paramagnetic substances are weakly attracted by a magnet. When placed in a non-uniform magnetic field, they slowly move from weaker parts of the field to stronger parts.
• Magnetic Susceptibility ($\chi$): They possess a small and positive magnetic susceptibility ($\chi > 0$).
• Relative Permeability ($\mu_r$): Their relative permeability is slightly greater than unity ($\mu_r > 1$).
• Effect of Temperature: According to Curie's Law, the magnetic susceptibility of paramagnetic substances is inversely proportional to the absolute temperature ($T$), i.e., $\chi \propto \frac{1}{T}$.
• Origin: Atoms or molecules of these substances have a net permanent magnetic dipole moment due to uncancelled electron spins.
• Examples: Aluminum, sodium, calcium, oxygen, and platinum.

3. Ferromagnetic Substances

• Behavior in Magnetic Field: Ferromagnetic substances are strongly attracted by a magnet. They rapidly move from weaker to stronger regions in a non-uniform magnetic field.
• Magnetic Susceptibility ($\chi$): They possess a very high and positive magnetic susceptibility ($\chi \gg 0$).
• Relative Permeability ($\mu_r$): Their relative permeability is very large (much greater than 1).
• Effect of Temperature: Above a specific temperature known as the Curie temperature ($T_c$), ferromagnetic substances convert into paramagnetic substances (Curie-Weiss law).
• Origin: They contain microscopic regions called domains where magnetic moments are aligned parallel to each other.
• Examples: Iron, cobalt, nickel, and various alloys likealnico.