Permanent magnet

Table of contents
- Curie temperature Permanent magnet
- Ferromagnetism Permanent magnet
  - Magnetic hysteresis Ferromagnetism
    - Saturation magnetisation Magnetic hysteresis

Ferromagnetism

The wiki comments: en.wikipedia.org/w/index.php?title=Ferromagnetism&oldid=965600553#Explanation

The Bohr-van Leeuwen theorem, discovered in the 1910s, showed that classical physics theories are unable to account for any form of magnetism, including ferromagnetism. Magnetism is now regarded as a purely quantum mechanical effect. Ferromagnetism arises due to two effects from quantum mechanics: spin and the Pauli exclusion principle.

Magnetic hysteresis

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To understand the graph, first learn/remember the difference between the magnetic B and H field.

The interest of the magnetic hysteresis graph is that it serves as an important characterization of a :

its area gives you the hysteresis loss of the transformer, which is a major cause of efficiency loss of the component
some key points of the curve give important characterizations of the core/material:
- Saturation magnetisation
- magnetization strength without field
- how much field you need to demagnetize it

This curve will also tell you how many turns of the coil will be needed to reach the required field.

Figure 1.
Theoretical magnetic hysteresis plot
. Source.

Video 1.

Measurement of B-H characteristic

. Source.

1989. 1989 and they were making such awesome materials. It is hard to understand why university still exists given this.

Shows how you can obtain the magnetic hysteresis curve with an AC source plus an oscilloscope in XY mode. youtu.be/pXukVix5Pcw?t=193 clearly shows the measurement circuit.

Video 2.

Magnetic hysteresis experiment by UNSW Physics.

Source.

2020, thanks COVID-19. Like other UNSW Physics YouTube channel videos, the experimental setup could be made clearer with diagrams.

But this video does have one merit: it shows that the hysteresis plot can be obtained directly with the oscilloscope XY mode by using an AC source. The Y axis is just a measure of the total magnetic field induced by the primary coil + the magnetization of the material itself.