Magnets at high and low temperatures: A comprehensive analysis of how temperature affects magnetism

Magnets are present in every aspect of our lives - from refrigerator magnets to electric car drive motors, from medical MRI machines to wind turbines. But did you know that a small fluctuation in temperature can significantly change the properties of a magnet? The relationship between temperature and magnetism is an eternal battle between order and chaos in the microscopic world.

Why are magnets so sensitive to temperature?

Magnets are magnetic because there are unpaired electrons in their internal atomic structure. Under certain conditions, the magnetic moments of these electrons will align with each other to form an orderly magnetic domain structure, which makes the magnet exhibit macroscopic magnetism. When the temperature changes, these microscopic structures will also change, which will affect the performance of the magnet.

First, high temperature is a "disruptor" of magnetism.

When a magnet is exposed to high temperature, its internal order gradually disintegrates:

Gradual demagnetization

The increase in temperature causes atoms in the magnet to vibrate violently, the magnetic domains begin to be arranged in disorder, and the magnetism gradually weakens12.

Ordinary neodymium magnets begin to experience reversible magnetic loss when they exceed 80°C (about 0.11% strength is lost for every 1°C increase).

Irreversible damage

If the temperature is far above the operating temperature but below the Curie point, it may cause irreversible loss (re-magnetization is required for recovery).

Exceeding the Curie temperature will cause permanent demagnetization, and the magnetism cannot be restored even if it is cooled.

On the contrary, low temperature has a more friendly effect on magnets

(i) Enhanced magnetism

In contrast to high temperature, low temperature environment usually enhances the magnetism of magnets. This is because the thermal motion of atoms is weakened at low temperature, the magnetic domain structure is more stable, and the arrangement of magnetic moments is more orderly. For example, in some low-temperature experimental equipment, when using magnets, it is found that their magnetism is stronger than at room temperature. This phenomenon is particularly evident in some special magnetic materials, such as some rare earth permanent magnets that can maintain high magnetic properties at low temperatures.

(ii) Increased material brittleness

Although low temperature can enhance the magnetism of magnets, it will also have an adverse effect on the physical properties of magnets. At low temperatures, the material of the magnet will become more brittle and easy to break. This is because low temperature enhances the intermolecular force of the material, while the thermal motion of atoms is weakened, resulting in a decrease in the toughness of the material.

(iii) Enhanced stability of magnetic domain structure

In low temperature environment, the magnetic domain structure inside the magnet is more stable. This is because the thermal motion of atoms is weakened at low temperature, the arrangement of magnetic domains is more orderly, and the direction of magnetic moments is more consistent. This stable magnetic domain structure enables the magnet to maintain strong magnetism at low temperatures, while also reducing the disordered changes in the magnetic domain structure.

Finally, different magnet materials respond to temperature very differently due to differences in composition and structure: