Magnetism and Matter for JEE & NEET
Magnetic Properties of Materials
Diamagnetism:
- Weak and temporary form of magnetism.
- Present in all materials but often masked by stronger magnetic effects.
- Atoms have no permanent magnetic dipole moment.
- When placed in an external magnetic field, they acquire a small induced magnetic moment in the opposite direction to the field.
- Examples: Water, copper, bismuth.
Paramagnetism:
- Weak form of magnetism.
- Atoms have permanent magnetic dipole moments due to unpaired electrons.
- These moments are randomly oriented in the absence of an external field.
- In an external field, the moments partially align with the field, resulting in a net magnetization in the same direction as the field.
- Examples: Aluminum, platinum, oxygen.
Ferromagnetism:
- Strong and permanent form of magnetism.
- Atoms have permanent magnetic dipole moments that strongly interact with each other.
- These interactions result in the formation of magnetic domains, regions where the atomic moments are aligned.
- In an external field, the domains align with the field, leading to a large net magnetization.
- Examples: Iron, nickel, cobalt.
Ferrimagnetism:
- Similar to ferromagnetism but with a weaker net magnetization.
- Occurs in materials with two types of atoms with different magnetic moments.
- The moments align in opposite directions, but the alignment is not complete, resulting in a net magnetization.
- Examples: Ferrites (iron oxides).
Origin of Magnetism in Materials
- Atomic Structure: The magnetic properties of materials arise from the behavior of electrons within atoms.
- Electron Spin: Electrons have an intrinsic angular momentum called spin, which gives rise to a magnetic dipole moment.
- Orbital Motion: The orbital motion of electrons around the nucleus also contributes to the magnetic moment of an atom.
- Exchange Interaction: In ferromagnetic and ferrimagnetic materials, a quantum mechanical interaction called the exchange interaction aligns the magnetic moments of neighboring atoms.
Magnetic Domains
- Definition: Magnetic domains are regions within a ferromagnetic material where the atomic magnetic moments are aligned.
- Domain Walls: Boundaries between domains where the magnetization direction changes.
- Magnetization Process: When an external magnetic field is applied, the domains aligned with the field grow at the expense of other domains, leading to a net magnetization.
Hysteresis
- Definition: Hysteresis is the phenomenon where the magnetization of a ferromagnetic material lags behind the applied magnetic field.
- Hysteresis Loop: A graph of magnetization versus applied field that shows the history-dependent behavior of the material.
- Remanence: The magnetization that remains after the external field is removed.
- Coercivity: The reverse field required to reduce the magnetization to zero.
Applications of Magnetic Materials- Magnetism and Matter for JEE & NEET
Magnetic materials have numerous applications in various fields, including:
- Data Storage: Hard drives, magnetic tapes.
- Electronics: Transformers, inductors, magnetic sensors.
- Medicine: Magnetic Resonance Imaging (MRI).
- Industry: Magnetic separators, lifting magnets.
Earth’s Magnetism
- Geomagnetic Field: The Earth has a magnetic field that resembles that of a bar magnet.
- Origin: The field is believed to be generated by electric currents in the Earth’s molten core.
- Magnetic Poles: The Earth’s magnetic poles are not located at the geographic poles.
- Applications: Navigation, compass.