What causes metals to become magnetically charged? And can you force a metal to have its north or south poles on certain sides?
In: Physics
There are actually (at least) _four_ types of material with respect to magnetic properties, and neither of the types described by the other response explain permanent magnetism which is what the OP is referring to. Diamagnetism and paramagnetism only result in a magnetisation within a magnetic field – as soon as the field is removed, the materials are demagnetised.
Permanent magnetism is a property of certain materials where the material retains its magnetisation even after an external field is removed. This property arises because of something known as ‘long-range order’ – essentially, certain metal ions have unpaired electrons in d orbitals that are so large that they can interact with electrons in neighbouring atoms. This means that, rather than atoms acting as individual magnets (as is the case in diamagnetism and paramagnetism), changes in the magnetisation of one atom affects the magnetisation of other atoms, and the result of these interactions beteen atomic magnetic fields results in large-range order. When the magnetic field is removed, individual atoms are no longer able to go back to having a random magnetisation because the interactions with the magnetisations of neighbouring atoms constrains them. There are a number of different subtypes of permanent magnetism which depend on the way the magnetic fields of different atoms interact, including ferromagnetism (where the magnetisations of all magnetic atoms are aligned) and ferrimagnetism (where the magnetisations are not aligned, but there is a dominant alignment), antiferromagnetism (where the magnetisations are not aligned and there is no dominant alignment), and canted antiferromagnetism (where the magnetisations are theoretically not aligned and have no dominant alignment, but crystal-field effects result in a small alignment).
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