Demagnetizing a magnet

[rthmjohn]

Just wondering... is it possible to demagnetize, say, a neodymium magnet? May sound stupid, but I'm just curious... (by demganetize I mean completely remove is magnetic field).

[woelen]

Just wondering... is it possible to demagnetize, say, a neodymium magnet? May sound stupid, but I'm just curious... (by demganetize I mean completely remove is magnetic field).

Dissolve the magnet in concentrated HNO3 or in aqua regia. The resulting solution certainly is not magnetic anymore .

[jdurg]

Dissolve the magnet in concentrated HNO3 or in aqua regia. The resulting solution certainly is not magnetic anymore .

 

 

Heh. With most magnets, I believe that if you increase the temperature of the magnet to a relatively high level you disrupt the magnetic field by altering the arrangment of the atoms within the metal. Gadolinium is one of the few elements, I believe, that will regain its magnetism upon cooling down. Heating up an iron magnet will destroy the magnetic field, as will a sharp physical 'attack'. I.E. if you hit a magnet hard enough you'll disrupt the magnetic field and it will lose its magnetism.

[swansont]

Heh. With most magnets, I believe that if you increase the temperature of the magnet to a relatively high level you disrupt the magnetic field by altering the arrangment of the atoms within the metal. Gadolinium is one of the few elements, I believe, that will regain its magnetism upon cooling down. Heating up an iron magnet will destroy the magnetic field, as will a sharp physical 'attack'. I.E. if you hit a magnet hard enough you'll disrupt the magnetic field and it will lose its magnetism.

 

That's the Curie temperature — the thermal energy is sufficient to break up the long-range ordering of a ferromagnetic material. Gadolinium's Curie temp is right around room temperature (293 K), so the magnetism is easily disrupted, but apparently has a very large magnetic moment, so it will become magnetic even with a weak external field.

[akcapr]

speaking of magnets, I have never really known why they are magnetic. Whats the the reason?

[swansont]

speaking of magnets, I have never really known why[/i'] they are magnetic. Whats the the reason?

 

Unpaired electron spins, combined with molecular structure. That's why relatively few materials are - electron spins tend to pair up, spin up + spin down, leaving no net magnetic field for the atoms.

[d22k]

OK, why are things magnetic in the 1st place?

 

what makes a negative electron attracted to a positive? (or more accurately them to each other...)

 

or is that just one of the things that "is cos it is"

[RyanJ]

OK' date=' why are things magnetic in the 1st place?

 

what makes a negative electron attracted to a positive? (or more accurately them to each other...)

 

or is that just one of the things that "is cos it is"[/quote']

 

Its actually a phyics question - probably best to ask that there, the answer should be interesting

 

Its like asking where gets its energy too move from I suppose.

 

Cheers,

 

Ryan Jones

[jowrose]

So it's all about the Pauli exclusion principle? But since electrons fill all the way across a sublevel, and then double up, wouldn't they be magnetic if their last shell was, say, 3d5? or 4d5? or 4f7? Or is there something i'm missing?

[swansont]

So it's all about the Pauli exclusion principle? But since electrons fill all the way across a sublevel, and then double up, wouldn't they be magnetic if their last shell was, say, 3d5? or 4d5? or 4f7? Or is there something i'm missing?

 

You have to have unpaired electrons and the ability to make a structure where the atoms can line up properly — you need the long-range order, i.e. above the atomic level. It does you no good if you have an atom with a magnetic moment if it always pairs up with other atoms in a way that cancels the field.

[rthmjohn]

Dissolve the magnet in concentrated HNO3 or in aqua regia. The resulting solution certainly is not magnetic anymore .

 

I meant without completely destroying the magnet itself.

[The Thing]

Neodymium magnets are pretty hard to demagnetize. Heating it above its Curie point will, of course, make it lose its magnetism. It's Curie point's quite low - 320 Celsius I think, but it begins to lose magnetism at a much lower temperature.

 

I have no clue as to how much current you need to put through a coil actuator to demagnetize a neodymium magnet, but I suspect that you will need a huge pulse.

 

As for the conventional ways to demagnetize weak magnets, such as banging the ---- out of them using a gigantic hammer, I'm not sure that it will work with neodymium magnets - most likely you'll crack the covering, and send pieces of the magnet flying around like bullets. Then the material inside will corrode. DON'T try it.

[rthmjohn]

Neodymium's pretty nasty stuff from what I'm told. United nuclear sells magnets that can pull objects from more than 10ft away. I'm guessing it would be futile to attempt to demagnetize these magnets.