Magnets are used in daily life. They’re used in manufacturing, automobiles, security systems and electronics devices. Even the earth itself is a magnet.

How does temperature affect the magnetism of magnets?

To understand temperature effects, we need to look at the atomic structure of the elements that make up the magnet. Temperature affects magnetism by either strengthening or weakening a magnet’s attractive force. A magnet subjected to heat experiences a reduction in its magnetic field as the particles within the magnet are moving at an increasingly faster and more sporadic rate. This jumbling confuses and misaligns the magnetic domains, causing the magnetism to decrease.  Conversely, when the same magnet is exposed to low temperatures, its magnetic property is enhanced and the strength increases.

In addition to the strength of the magnet, the ease at which it can be demagnetized also varies with temperature. Like magnet strength, demagnetization resistance generally decreases with increasing temperature. The one exception is ceramic (ferrite) magnets, which are easier to demagnetize at low temperature and harder to demagnetize at high temperature.

Different magnet materials react differently with temperature. Alnico magnets have the best strength stability followed by SmCo, NdFeB, and then ceramic. NdFeB magnets having the highest resistance to demagnetization (coercivity), but the largest change with temperature. Alnico magnets have the lowest resistance to demagnetization, but the smallest change with temperature. Alnico have the highest service temperature followed by SmCo, ceramic and then NdFeB.

Not everyone realizes that the shape of a magnet affects its maximum usable temperature. This is especially important for NdFeB magnets because they have the greatest change in demagnetization resistance with temperature. As the length of the magnetized axis increases, its resistance to demagnetization also increases.

How does temperature affect magnetism of reed switches?

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.

Do not expect all switches to track identically with temperature. There will be variations in the amount of pull-in change with temperature – less if the switch type and pull-in are the same, more if the switch type and pull-in vary.

Lower pull-in switches have the advantage of less pull-in change with temperature because they are working at a lower point on the magnetization curve.HSI Sensing manufactures reed switches and proximity sensor actuators with various magnetic materials depending on application requirements.

HSI Sensing manufactures reed switches and proximity sensor actuators with various magnetic materials depending on application requirements.

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Published On: May 9th, 2017 / Categories: Innovations, Making Sense, Research & Development / Tags: , , /

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