What magnets undergo noticeable reversible losses at everyday temperatures?

Question

I plan on buying magnets for an experiment investigating the relationship between magnet temperature and pull strength (at a consistent distance).

What magnets would be best for this experiment? The temperature ranges I am considering are -10 to 80 degrees Celsius. Ideally, a magnet would be sensitive to temperature change, so there would be noticeable changes in force (will this even be noticeable).

Any help would be greatly appreciated!

Answer 1

Commonly available magnets that also have a temperature-sensitive magnetic strength at low-ish temperatures are neodymium N-type magnets, whereas ferrite magnets have a higher resistance to temperature. It's important to differentiate three phases as the temperature rises and magnetic energy density decreases:

1. reversible loss of magnetism - this happens at temperatures slightly above the stated maximum operating temperature, usually about 80 °C, but there are high-temperature magnets that have higher operating temperatures. Once the magnet cools down below its maximum operating temperature, it will regain it's strength.
2. irreversible loss of magnetism - once you heat up the magnet well above its maximum operating temperature, it will lose some of its magnetic strength and not regain it even after cooling down. It can still be re-magnetized by exposing it to a strong external magnetic field, however.
3. complete loss of magnetism - this happens above the Curie temperature, about 310 °C for neodymium magnets. After this point, the magnet is paramagnetic instead of ferromagnetic and will no longer attract to magnetic surfaces.

So, with the temperature range you stated (-10 °C to 80 °C), I don't think you will see strong measurable effects. Going hotter should show some results, though. Designing a proper measurement process is left as an exercise to the reader ;)