Does the force of the magnet decrease over time?

When everyday language is spoken of as magnets, reference is usually made to ferromagnetism. Examples of ferromagnetic substances are iron, nickel and cobalt and their compounds.

Ferromagnetism has its roots in the atomic level of matter. The orbital motion of electrons around nuclei forms current loops, or small magnetic moments. In a ferromagnetic material, elementary regions are created within which these magnetic moments are arranged parallel to each other.

A ferromagnetic material becomes a magnet when a sufficiently large part of its elementary regions are arranged in parallel. This can happen, for example, near another strong magnet.

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Permanent magnets are made of materials that have the ability to maintain the order of elementary regions for a very long time. Over time, small changes in temperature, random external magnetic fields, and mechanical movement affect the magnet. They increase the disorder between the elementary regions, which reduces the strength of the magnet.

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However, the phenomenon is rather slow. If the permanent magnet is carefully stored and its poles connected to each other with an iron body, it can retain its magnetic properties for years to come. Permanent magnets made from alloys of rare earth metals such as neodymium can last up to centuries as magnets.

A sufficiently high temperature or a magnetic field in the opposite direction can also discharge the magnetism. For example, at more than 770 degrees Celsius, an iron permanent magnet returns to a regular piece of iron.

The defendant is Antti-Jussi Kallio

doctoral researcher, University of Helsinki.

Published in Science 7/2022.

Source: Tiede by

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