12: Properties of Magnetic Materials
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- 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 μoH=μonI. If we now place an iron rod of permeability μ inside the solenoid, this doesn't change H, which remains nI. The B-field, however, is now B=μH. This is greater than μoH, and we can write B=μo(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 +103 or 104 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. (http://www.itacanet.org).