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Like magnets, reed switch magnetism decreases at higher temperature and increases at lower temperature. This is because high temperatures increase random atomic movement and misalignment of magnetic domains. As a result, more magnetism needs to be applied to the reed switch at high temperature. In other words, the pull-in goes up as the temperature increases. Depending on the type of switch, its sensitivity (pull-in) and the temperature range, this effect can be inconsequential or significant.

https://hsisensing.com/temperature-affect-magnetism/

It seems to imply that temperatures affect magnetism. While I know that high temperature can impact magnetism negatively, I am wondering if the opposite is true and to what extent? Also, does it apply to all magnets, or certain type of magnets? I couldn't find a single source that explained everything about magnetism and temperature, and how it can be generalized across all magnetic materials.

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On the surface this is a simple question since we usually think of ferromagnets and those are what are used in reed switches. As the temperature is increase the magnetic domains are not as aligned, and above the Curie temperature the material no longer has magnetic domains and has become Paramagnetic. Paramagnets don't produce a strong magnetic field. If you want a strong ferromagnet you place the material in a very strong magnetic field and all the domains line up and are frozen in place, so when you take it out of the strong magnetic field, the magnetic field of the domains are aligned as much as they could be, so as you lower the temperature the magnetic field doesn't change.

However, there are several types of magnetism. Other materials are naturally Paramagnetic, or Diamagnetic or Antiferromagnetic and will have Curie points or Neel points depending on the material and those points will depend on the type of material.

The way you classify these material is by defining a magnetic susceptibility.

Magnetic susceptibility is a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field.

If the Magnetic susceptibility is positive you have a paramagnetism, if it is negative you have diamagnetism. Ferromagnets are paramagnetic materials where below the Curie temperature you can form domains where the magnetic moments are aligned to be in a lower energy configuration.

So one way to answer your question is to look at how the magnetic susceptibility changes as a function temperature.

When you do this you find that some materials are paramagnets at higher temperatures, but below the Neel point start to have a magnetic field, and this is called Antiferromagentism and in that case as you lower the temperature you can also have magnet.

In general to understand all the details, it comes down to understanding if the electron spins are paired or unpaired, and if there is a net magnetic moment of the material.

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