How do permanent magnets lose their magnetism?

Why are permanent magnets magnetic?

Microscopically, the negatively charged electrons are spinning themselves while constantly revolving around the nucleus. The rotation of electrons creates an attractive or repulsive force, which we call magnetism. In most elements, the electrons in the same orbit have opposite spin directions, and the magnetic moments cancel each other out, showing no magnetism. Otherwise, in some elements such as iron, nickel, cobalt, the electron layer contains unpaired electrons, the magnetic moments cannot cancel each other, these elements have the potential to show magnetism, which we call ferromagnetism. The magnetic moments of electrons in these elements are disorderly arranged, they do not show magnetism in the natural state. Under the influence of external magnetic fields, the magnetic moments of electrons in ferromagnetic materials arrange themselves, showing magnetism on a macroscopic level, forming permanent magnets.

 

The effect of temperature on permanent magnets

Although the macroscopic magnet may appear calm and impermanent on the surface, at the microscopic level, the atoms are constantly vibrating. The increase of temperature will intensify the vibration of atoms, thus affecting the arrangement of the magnetic moment of the permanent magnet, destroying the original arrangement direction of the magnetic moment, so that the magnet loses its magnetism. Permanent magnets are usually marked with a maximum operating temperature to avoid demagnetization of the permanent magnets.

Does the impact damage the magnet?

The violent impact knocks the magnet’s atoms into each other, causing them to rearrange randomly, destroying the magnetism. Samarium Cobalt magnets, Ferrite magnets are both very brittle and can cause structural damage if dropped on hard ground. Compared with the two magnets mentioned above, Neodymium magnets have better mechanical strength, but they are still relatively brittle materials. In addition, AlNiCo magnets are very strong and generally do not suffer mechanical damage.
Corrosion can also damage the structure of the magnet. Neodymium magnets, in particular, are very susceptible to corrosion and generally require coating to protect them.

Does the permanent magnet demagnetize naturally?

No “permanent magnet” is completely permanent. Magnets will demagnetize over time, but we don’t need to worry about that at all. Studies have shown that it takes about 700 years for a rare earth samarium cobalt magnet to lose its half magnetic strength.

Magnets effect by external magnetic fields

The ability of magnets to resist the influence of magnetic fields is called coercive force, which is an important indicator to measure the performance of magnets. If magnetic demagnetization is not desired, exposure of the magnet to a reverse magnetic field that exceeds its coercive force needs to be avoided.

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