Demagnetise permanent magnet

Bodies made of ferromagnetic materials are not only attracted by magnets but can also experience magnetization themselves when they are touched. A ferromagnetic object holds countless tiny so-called elementary magnets. These are arranged in many individual domains, the Weiss districts named after their discoverer, and are aligned in the same way within these areas. The resulting small magnetic fields are not sufficient to give the body magnetic force because the domains are not synchronized with each other, and the magnetic fields cancel each other out.

How exactly does demagnetizing a permanent magnet work?

Only the application of an external magnetic field and the resulting attraction or adhesion ensure that all elementary magnets align themselves in the same way in their Weiss areas. The domain walls shrink, fold over and the rectified field strength due to the now synchronized and superimposed partial magnetic fields increases significantly.

If it is a magnetically hard material such as ferrite or neodymium, the resulting magnetization is retained, even if the external magnetic pole is no longer present. Magnetically soft materials, on the other hand, experience demagnetization just as quickly as magnetization. This means that the individual elementary magnets in the Weiss areas randomly align themselves again and the magnetic field strength decreases accordingly.

However, if a magnetically harder metal that has been magnetized needs to be demagnetized again, specific steps are necessary.

The magnetization and demagnetization of a metallic body is based on the principle of influencing the alignment of the individual elementary magnets.
After these have been aligned uniformly during the magnetization process, it is then necessary to dissolve this so-called integrity if you want to demagnetize a magnet yourself.
This in turn causes the individual electron spins to re-align themselves inconsistently in the Weiss areas. Due to the opposing directions in the domains, the magnetic fields are again compensated for, and the magnetic effect of the body is extinguished.

Permanent magnets can be demagnetized using various methods. This includes:

  • Heating
  • Cooling down
  • Shaking
  • Creation of an alternating current field
  • Applying a high magnetic field strength
  • temporal decomposition (corrosion, oxidation)
Magnet manufacturers prevent temporary decomposition by applying nickel or epoxy resin coatings or by mixing the magnetic metals with cobalt.

How does the demagnetization of a permanent magnet with the help of heat and vibrations work?

Raising the temperature is a reliable way to demagnetize even strong permanent magnets. This is because these are only unrestrictedly magnetic in a certain temperature range and up to their so-called Curie temperature. Above this limit, which for the particularly strong neodymium magnets is, for example, 80 degrees Celsius, the elementary magnets arrange themselves again freely. This significantly reduces the magnetization. The phase transition is now complete.

Some ferromagnetic materials, including ferrite magnets and magnetic foils and tapes, also lose their magnetic properties if they get too cold. For example, ferrite magnets lose their full magnetization both at more than 250 degrees Celsius and at less than -40 degrees Celsius.

Vibrations are somewhat less reliable and particularly effective for weaker magnets. If, for example, the end of a permanent magnet is struck with a hammer, this can also result in the electron spin order dissolving within the said body.

How can another strong magnetic field demagnetize a magnet?

A sufficiently strong opposing magnetic field can also cancel the magnetization of a body. This must be of opposite polarity and have a suitable coercive field strength. This is a field strength that is suitable to reduce the magnetic flux density or permeability of the magnetized body sufficiently and to rotate the electron spins. However, the rotation should not be so strong that it creates a magnet again, which is only polarized in the opposite direction.

Other magnets as well as alternating current fields, which can be generated with the help of solenoid valves (copper wire loops around metal cores through which electricity flows), are suitable for such a process.


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