Demagnetizing Magnets: Alternating & Direct Currents

[Gomide Math]

Is it possible to demagnetize a magnet using alternating current? How does this happen?
And is direct current also possible?

 

[kuruman]

Hi Gomide Math and welcome to PF.


It is possible. See, for example

https://www.thoughtco.com/how-to-demagnetize-a-magnet-607873

Direct current would not work because it will not randomize the magnetic dipole moments in the magnet.

 

[alan123hk]

Ferromagnetic materials can be demagnetized by decaying alternating field.

Please refer to https://cestriom.com/en/technology/demagnetization-basics/ to show the demagnetization diagram with decaying alternating field.

 

[sophiecentaur]

Is it possible to demagnetize a magnet using alternating current? How does this happen?
And is direct current also possible?

The equipment needed for this depends on the size of the object you want to demagnetise. If you want to use an electrical 'Degausser', you can start with it switched off, turn the control to Max (current through the coils) and then slowly turn the control down to minimum. Alternatively, you can hold the object next to a degausser with no current control, turn it on and slowly separate the object and the degausser. This has the same effect of applying a decreasing alternating field to the object.

There are many cheap electrical degaussers on the market for degaussing small items. Also, there are small (20mm cube) which contain small, strong permanent magnets which you can stroke small screwdrivers etc. over. I bought one and the 'iron filings' test shows it works fairly well. There must be two or more magnets in them with a weird field distribution inside. Surprisingly successful after I was so skeptical when I read the eBay adverts! The very high fields you can get with modern magnets allow all sorts of tricks with permanent magnets.

Alternatively, again, I made up a disc with strong button magnets in a circle facing in alternate directions NS. SN. NS. SN. etc. With the disc rotated on a drill or lathe, more or less any hand tool can be demagnetised by sliding it across the face of the disc. Good enough to pass the iron filing pick up test and a nice little project, making it.

But the fields you need are higher than the original magnetisation. So demagnetising a 'magnet' would be more of a problem. Roasting it could perhaps partly do the trick.