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Physics LibreTexts

12: Properties of Magnetic Materials

  • Page ID
    5493
  • [ "article:topic-guide", "authorname:tatumj" ]

    • 12.1: Introduction
      We have defined the magnetic fields \(B\) and \(H\). To define \(B\), we noted that an electric current situated in a magnetic field experiences a force at right angles to the current, the magnitude and direction of this force depending on the direction of the current. We accordingly defined \(B\) as being equal to the maximum force per unit length experienced per unit current,
    • 12.2: Magnetic Circuits and Ohm's Law
      Some people find it helpful to see an analogy between a system of solenoids and various magnetic materials and a simple electrical circuit. They see it as a "magnetic circuit".
    • 12.3: Magnetization and Susceptibility
      The \(H\)-field inside a long solenoid is \(nI\). If there is a vacuum inside the solenoid, the B-field is \( \mu_o H = \mu_o nI\). If we now place an iron rod of permeability \(\mu\) inside the solenoid, this doesn't change \(H\), which remains \(nI\). The B-field, however, is now \(B=\mu H\). This is greater than \(\mu_oH\), and we can write \[B = \mu_o(H+M) \]
    • 12.4: Diamagnetism
      Diamagnetic materials have a very weak negative susceptibility. All materials are diamagnetic, even if their diamagnetism is hidden by their greater para- or ferromagnetism.
    • 12.5: Paramagnetism
      Diamagnetism makes itself evident in atoms and molecules that have no permanent magnetic moment. Some atoms or molecules, however, do have a permanent magnetic moment, and such materials are paramagnetic. They must still be diamagnetic, but often the paramagnetism will outweigh the diamagnetism. The magnetic moment of an atom of a molecule is typically if order of a Bohr magneton.
    • 12.6: Ferromagnetism
      What we normally think of as magnetic materials are technically ferromagnetic. The susceptibilities of ferromagnetic materials are typically of order \(+10^3\) or \(10^4\) or even greater. However, the ferromagnetic susceptibility of a material is quite temperature sensitive, and, above a temperature known as the Curie temperature, the material ceases to become ferromagnetic, and it becomes merely paramagnetic.
    • 12.7: Antiferromagnetism
      The susceptibility of an antiferromagnetic material starts at zero, and its transformation to a paramagnetic material results in an increase (albeit a small increase) in its susceptibility.
    • 12.8: Ferrimagnetism
      Ferrimagnetics have domain structure with alternate magnetic moments that are pointing in opposite directions. But this does not result is complete cancellation of the magnetization of a domain.

    Thumbnail: A piece of ferromagnetic material which is not magnetized, where the domain poles are not aligned. Image used with permission (http://www.itacanet.org).