Magnetic Properties of Materials

Classification of Magnetic Materials

Magnetic materials are classified based on the magnetic dipole moments of their atoms. Atoms may or may not have a permanent magnetic dipole moment, and this determines their magnetic behaviour.

  1. Diamagnetic materials: The materials are made up of atoms that have no permanent magnetic dipole moment.
    Examples: Bismuth, Copper, Silver.
  2. Some atoms or molecules have a permanent magnetic moment. These materials are further divided into four types depending on how the atomic magnetic dipoles interact with each other:
    • If the interaction between magnetic dipoles is very weak or negligible, the material is called paramagnetic. Dipoles align partially when an external magnetic field is applied but return to a random orientation when the field is removed.
      Example: Aluminum, Platinum.
    • Dipoles interact strongly and align in the same direction, even without an external magnetic field. Such materials are called ferromagnetic. They show strong magnetism and can become permanent magnets.
      Example: Iron, Cobalt, Nickel.
    • Neighboring dipoles align in exactly opposite directions, giving antiferromagnetic behavior. The dipoles have equal magnitude, so they cancel each other, resulting in zero net magnetization.
      Example: Manganese Oxide (MnO).
    • Dipoles align in opposite (antiparallel) directions, but their magnitudes are not equal. So, they do not cancel completely and produce a net magnetization. These materials are called ferrimagnetic.
      Example: Magnetite (Fe₃O₄).
S.No. Diamagnetic Paramagnetic Ferromagnetic
1 No magnetic moments Randomly oriented magnetic moments Domains with parallel magnetic moments
2 Negative susceptibility Positive, less than 1 Large and positive susceptibility
3 Weakly repelled by magnetic field Weakly attracted Strongly attracted
4 Less field lines inside More field lines inside Field lines concentrated
5 No hysteresis No hysteresis Shows hysteresis
6 Bismuth, Mercury, Silver Platinum, Chromium, Aluminum Iron, Cobalt, Nickel
7

MCQs on Classification of Magnetic Materials

  1. Diamagnetic materials are those in which:
    • a) Atoms have strong permanent dipole moments
    • b) Magnetic dipoles align spontaneously
    • c) Atoms have no permanent magnetic dipole moment
    • d) Magnetic dipoles align opposite but unequal
    Answer

    c) Atoms have no permanent magnetic dipole moment

  2. When magnetic dipoles align strongly in the same direction, the material is:
    • a) Diamagnetic
    • b) Paramagnetic
    • c) Ferromagnetic
    • d) Antiferromagnetic
    Answer

    c) Ferromagnetic

  3. In antiferromagnetic materials:
    • a) Dipoles align randomly
    • b) Dipoles align in opposite directions with equal magnitude
    • c) Dipoles align parallel and strong
    • d) Dipoles align opposite with unequal magnitude
    Answer

    b) Dipoles align in opposite directions with equal magnitude

  4. Ferrimagnetic materials differ from antiferromagnetic materials because:
    • a) They show no net magnetization
    • b) They have unequal opposite dipole moments, giving net magnetization
    • c) They repel magnetic fields strongly
    • d) They behave like superconductors
    Answer

    b) They have unequal opposite dipole moments, giving net magnetization

  5. Paramagnetic materials:
    • a) Are strongly attracted by magnetic fields
    • b) Are repelled by magnetic fields
    • c) Are weakly attracted due to small permanent dipole moments
    • d) Cannot be magnetized at all
    Answer

    c) Are weakly attracted due to small permanent dipole moments