How do you magnetize a circular magnet?

[David Lewis]

Yes. Sintered NdFeB has the highest energy density.

 

[Part Toon]

Yes. Sintered NdFeB has the highest energy density.

Thanks for the info :)

I will most likely re-magnetize a neodymium ring in the way like DrZoidberg said :D

I may still need some info on the subject, please continue to fill my brain with magnet stuff

 

[NascentOxygen]

We don't know how strong a magnet is desired. All we know is that it should have almost no detectable "external" field. So does it really matter how strong it is? Perhaps a weaker magnet may be preferable, as this would minimize the detectable exterior field.

I'm not convinced that heating a neodymium magnet above its Curie temperature will scramble the domains so completely that when cooled it will then show no trace of that former orientation. The way I read this, merely losing merely 99.9% of a neodymium magnet's original field will not be enough loss here!

Fortunately, with low material costs there is no barrier to experimentation.

 

[Part Toon]

We don't know how strong a magnet is desired. All we know is that it should have almost no detectable "external" field. So does it really matter how strong it is? Perhaps a weaker magnet may be preferable, as this would minimize the detectable exterior field.

I'm not convinced that heating a neodymium magnet above its Curie temperature will scramble the domains so completely that when cooled it will then show no trace of that former orientation. The way I read this, merely losing merely 99.9% of a neodymium magnet's original field will not be enough loss here!

Fortunately, with low material costs there is no barrier to experimentation.

I found a wikipedia page containing a list of ferromagnetic materials...

https://en.wikipedia.org/wiki/Category:Ferromagnetic_materials

Would any of these work in the manner of heating, slowly cooling, and re-magnetizing?

Please share your thoughts

 

[nasu]

The rare-earth magnets have a very strong magnetic anisotropy. This means they can be magnetized much easier along one direction than along other directions.
They are manufactured so that the "easy" direction is along the desired magnetization of the finite magnet.
So trying to demagnetize and magnetize along a different direction may not be such a good idea.

 

[OmCheeto]

I found a wikipedia page containing a list of ferromagnetic materials...

https://en.wikipedia.org/wiki/Category:Ferromagnetic_materials

Would any of these work in the manner of heating, slowly cooling, and re-magnetizing?

Please share your thoughts

I see iron on the list, and I seem to have a fan of my "just magnetize a flat washer" idea:

@OmCheeto mentioned a flat washer. Could you permanently magnetized one with a coil, then remove the coil?

I'm still wondering about what you'd inspect one of these things for when you go shopping.

...I'd prefer it'd be some sort of store that I can examine the magnet in person before purchase...

Are you wanting to make sure it's the right color, as

Ampere's Law: Magnetic Field Inside a Toroid
...
Magnetic field outside: negligibly weak.
...

It's quite possible, though very improbable, that every flat washer at the corner hardware store, is already magnetized, in the manner in which you are seeking.I think this is why everyone is still mostly confused about what you are doing, as aside from old fashioned computer memory, your magnet would have no function.

 

[anorlunda]

It's quite possible, though very improbable, that every flat washer at the corner hardware store, is already magnetized, in the manner in which you are seeking.

That's brilliant. So true, yet so counter-intuitive.

 

[OmCheeto]

That's brilliant. So true, yet so counter-intuitive.

It's not a good idea, to encourage me.

 

[Charles Link]

One question I have is how will you probe the magnetized ring to even know if it is magnetized? Wire transformer type loops is one way to measure a change in the magnetism. If the magnetization vector is circular inside the material, I think most of the magnetic field will be inside the material with little external field. You could change the direction of magnetization, assuming it is permanent, with a single current carrying wire through the hole in the center, but it might take very strong currents to have any effect.

 

[rootone]

How about you could obtain a lot of standard bar magnets, say 120 or so of them, then arrange them end-on-end into a circle.

 

[OmCheeto]

How about you could obtain a lot of standard bar magnets, say 120 or so of them, then arrange them end-on-end into a circle.

I have 338 bar magnets.
I tried it yesterday, and again this morning.
It doesn't work
You would have to build some type of frame to hold them in position.
Free form stuck to my refrigerator, I estimate you would need at least a couple of thousand.
And even then, I don't think it will work, as even when they are all in a straight line, there is detectable flux leakage between each magnet. Not much, but detectable.

edit: Oh, and by the way, the OP wants it to be only 1.5 inches in diameter. My ring of magnets would probably be 10 feet in diameter. And they are each only 4 mm long.

 

[rootone]

Yes I was assuming there would need to be a frame.
Maybe flux leakage could be reduced by placing a small neutral iron spacer between each bar, but they would need to be a precise wedge shape though to make the circle as much as possible continuous, which is getting a little complicated.

edit:
I overlooked the fact that this has to be small in size.
That doesn't rule out the idea in principle, but it does mean very high precision micro engineering, so probably not practically feasible

 

[Part Toon]

I can tell that there's been a lot of talk since last time I looked :P As I have said before, the magnet must be as a single piece, it simply cannot be multiple pieces, as OmCheeto said...

And even then, I don't think it will work, as even when they are all in a straight line, there is detectable flux leakage between each magnet. Not much, but detectable.

For there is slight flux leakage, for my purposes, this can completely ruin the function of my device, the flux lines must be pure without any escaping flux lines to create poles :P

I do need it to be one piece, there may not be many flux lines penetrating into the outside of the magnet, but I only need a little for my experiment.

I was thinking (as for the material) iron oxide. Remember this post that I shared a while ago?

http://www.ebay.com/itm/Green-Iron-74mm-Outside-Diameter-Power-Ferrite-Toroid-Core-T73-/310839060200?hash=item485f73a6e8:g:bOcAAOSwDNdVlYhN#rpdCntId

I'm sure that it's not the correct magnet that I need, but ferrite (iron oxide) as I have heard from wikipedia, has a relativily low curie temperature of about 850 degrees F. So I can remove the (most likely rubberized) coating, heat it up in a furnace that I have at the farm, and then I can do the coily thing, pump a lot'o electricity into the coil going around the magnet, and then presto! I got my mystery magnet that I'm looking for

If there's anything wrong with my potential plan (like some sort of radiation coming from the ferrite when heated, or the coils, or something else), please tell me :)

EDIT: Here is the system I use for testing my device, I get an idea, I build it, it usually doesn't work, I take a break, I think about it, I find out what's wrong with it, I correct my errors, repeat...

 

[Charles Link]

As I asked in post #39, are you planning on having a couple of loops of wire to probe these magnets? (You would need insulated wire). Connecting it to an oscilloscope, you should be able to observe a voltage change (=Faraday EMF)in the wire loops as the iron becomes magnetized or demagnetized. If the voltage you see is just from the changing magnetic field from the magnetizing wire, it would be considerably less. If the iron becomes magnetized, it should show an appreciable voltage (perhaps 50 mV depending upon the number of loops you use) as the iron becomes magnetized.

 

[Part Toon]

As I asked in post #39, are you planning on having a couple of loops of wire to probe these magnets? (You would need insulated wire). Connecting it to an oscilloscope, you should be able to observe a voltage change (=Faraday EMF)in the wire loops as the iron becomes magnetized or demagnetized.

I probably would not, for I do not have an oscilloscope :P

 

[Charles Link]

I probably would not, for I do not have an oscilloscope :P

An oscilloscope can come in very handy for such research. It might be worthwhile to consider borrowing one or renting one.

 

[Part Toon]

An oscilloscope can come in very handy for such research. It might be worthwhile to consider borrowing one or renting one.

I believe you

How much would one usually cost?

Also, do you think my plan might work for obtaining my mystery magnet?

I was thinking (as for the material) iron oxide. Remember this post that I shared a while ago?

http://www.ebay.com/itm/Green-Iron-74mm-Outside-Diameter-Power-Ferrite-Toroid-Core-T73-/310839060200?hash=item485f73a6e8:g:bOcAAOSwDNdVlYhN#rpdCntId

I'm sure that it's not the correct magnet that I need, but ferrite (iron oxide) as I have heard from wikipedia, has a relativily low curie temperature of about 850 degrees F. So I can remove the (most likely rubberized) coating, heat it up in a furnace that I have at the farm, and then I can do the coily thing, pump a lot'o electricity into the coil going around the magnet, and then presto! I got my mystery magnet that I'm looking for

If there's anything wrong with my potential plan (like some sort of radiation coming from the ferrite when heated, or the coils, or something else), please tell me :)

I hope it will work, I'm starting to run out of ideas for how to build my secret device (I've been doing this for 3 years), since I was stumped in how to get such a circular magnet, I decided to make a PF account to see if it would help, so far it has

 

[Charles Link]

I think an oscilloscope might cost a couple thousand dollars, but it also takes some time/practice to get good at using one. One other suggestion would be to try to hook up with someone who has one and is handy with it. It would be so useful to experimentally monitor the changes in the magnetism with a couple loops of wire, etc. connected to an oscilloscope. I think you would find experiments using this type of probe extremely useful as well as very interesting.

 

[NascentOxygen]

I decided to make a PF account to see if it would help, so far it has

A PF account won't help if you disregard whatever you don't want to hear.

Something sold as a ferrite core is for an electromagnet, it's made of material which does not retain magnetism. It's the wrong type of ferrite for a permanent magnet.

I have not tried heating a ferrite core, but it's just a compressed powder so I'd expect it may well crumble to a powder if heated in a furnace. But I'd welcome being proved wrong.[/size]

I think your best course is to get a steel band or washer from a wreckers or a repair shop and use it. Test with a compass needle to see whether it has any measurable unwanted field, and if not, go ahead and magnetize it how you want using a solenoid.

 

[Part Toon]

A PF account won't help if you disregard whatever you don't want to hear.

Something sold as a ferrite core is for an electromagnet, it's made of material which does not retain magnetism. It's the wrong type of ferrite for a permanent magnet.

I have not tried heating a ferrite core, but it's just a compressed powder so I'd expect it may well crumble to a powder if heated in a furnace. But I'd welcome being proved wrong.

I think your best course is to get a steel band or washer from a wreckers or a repair shop and use it. Test with a compass needle to see whether it has any measurable unwanted field, and if not, go ahead and magnetize it how you want using a solenoid.

Okay, ferrite (or at least the kind in the said magnet) might not work for me :P However, there are plenty of other ferromagnetic materials such as iron, how would one magnetize a piece of iron, would it also be done with solenoid? I could probably get a ferromagnetic iron ring relatively easy (although, I may be wrong). There may also be a different ferromagnetic material that could go through my process of removing the covering, heating above curie, slowly cooling, and re-magnetizing. If there is a better material (hopefully one with a low-ish curie temperature {nothing more than 1000 degrees F), and that won't cost $100 to get a pound of it :P) then please tell me

 

[NascentOxygen]

As I asked in post #39, are you planning on having a couple of loops of wire to probe these magnets? (You would need insulated wire). Connecting it to an oscilloscope, you should be able to observe a voltage change (=Faraday EMF)in the wire loops as the iron becomes magnetized or demagnetized. If the voltage you see is just from the changing magnetic field from the magnetizing wire, it would be considerably less. If the iron becomes magnetized, it should show an appreciable voltage (perhaps 50 mV depending upon the number of loops you use) as the iron becomes magnetized.

While soundly based on theory, this is somewhat impractical^‡ here. The comparison is relatively subtle, and OP is not using a repetitive signal.
^‡ though it would make for a fascinating lab demonstration!

If there is a need to demonstrate that the ring has become magnetized, then perhaps a second sacrificial one should be created in a manner identical to the first, and this second magnet cut through with a hacksaw to reveal its hidden field.

 

[Part Toon]

While soundly based on theory, this is somewhat impractical^‡ here. The comparison is relatively subtle, and OP is not using a repetitive signal.
^‡ though it would make for a fascinating lab demonstration!

If there is a need to demonstrate that the ring has become magnetized, then perhaps a second sacrificial one should be created in a manner identical to the first, and this second magnet cut through with a hacksaw to reveal its hidden field.

So...

Would iron be a good substitute for ferrite? Or maybe something different?

EDIT: Also, would my plan (excluding the mystery material) work as for demagnetizing and re-magnetizing? Please share your thoughts.

 

[Charles Link]

While soundly based on theory, this is somewhat impractical^‡ here. The comparison is relatively subtle, and OP is not using a repetitive signal.
^‡ though it would make for a fascinating lab demonstration!

If there is a need to demonstrate that the ring has become magnetized, then perhaps a second sacrificial one should be created in a manner identical to the first, and this second magnet cut through with a hacksaw to reveal its hidden field.

I do think with a single sweep on the oscilloscope using (part of) the magnetizing current as a trigger, you could determine whether you succeeded in changing the magnetic state (e.g. reversing the direction of the permanent magnet). An increased signal response ( a healthy pulse) on the probe coil when the change occurred would be a clear indicator.

 

[Part Toon]

I am thinking of getting a permanent magnet in the shape of a ring, removing any covering (if any), heating it above curie, slowly cooling so that magnetism will not be reintroduced, and then re-magnetize it by using a solenoid in the way that I require :D

Please share your thoughts for if my plan might work or not...

 

[Charles Link]

Heating above the Curie temperature and magnetizing on cooling is perhaps the best way to make a high-quality permanent magnet. (I've only read about the process of doing this-I've never performed experiments of taking the material above the Curie temperature and then back down.) If you already have a good permanent magnet, the heating process would be unnecessary. As NascentOxygen has pointed out, your choice of materials is important. Different magnetic materials have totally different properties on whether they make good permanent magnets or simply make a bunch of domains pointing in every direction upon removal of the applied field, etc. If you do begin with a permanent magnet, it will most likely take a healthy magnetic field in the opposite direction to reverse the direction of permanent magnetism. Two approaches could be used= 1)a strong current pulse running on a single thick and insulated wire down the center, or 2) wrapping the washer like a solenoid (again using insulated wire) to apply the magnetic field. As previously mentioned, a few loops of wire should work well as a probe which is best monitored with an oscilloscope.

 

[Part Toon]

Heating above the Curie temperature and magnetizing on cooling is perhaps the best way to make a high-quality permanent magnet. (I've only read about the process of doing this-I've never actually performed any such experiments.) If you already have a good permanent magnet, the heating process would be unnecessary. As NascentOxygen has pointed out, your choice of materials is important. Different magnetic materials have totally different properties on whether they make good permanent magnets and/or simply make a bunch of domains pointing in every direction upon removal of the applied field, etc. If you do begin with a permanent magnet, it will most likely take a healthy magnetic field in the opposite direction to reverse the direction of permanent magnetism. Two approaches could be used= 1)a strong current pulse running on a single thick and insulated wire down the center, or 2) wrapping the washer like a solenoid (again using insulated wire) to apply the magnetic field.

My older brother has a blue magnet that he likes to call "The Chuck Magnet", I have no idea why. It is literally the exact size that I'd need (maybe a bit smaller). One time, I tried to re-magnetize it with a solenoid made of copper wire, however, it didn't work at all, for many reasons now that I look back. The magnet had a rubberized coating (which would prevent the electric currents from entering the magnet), the wire was not insulated (which I'm not sure if it would have affected it that much, but like I said, I'm not sure), and I was only using 12 volts of electricity (my mom didn't want me to electrocute myself :P). I'm sure if I change out some of these variables and try again, that it'd work (although, I may want to get a different magnet first, we like to use the "Chuck Magnet" to pick up loose nails and stuff hiding in the dirt)

So which variables do you think need changing? If not all of them :P

 

[Charles Link]

Any solenoid you use to magnetize it must be insulated wire. You could do well to read about solenoids and magnetic fields=The field from the solenoid becomes stronger with stronger DC currents and also with more turns per unit length. When running high amounts of DC current through the solenoid (e.g. 1 or 2 amps or even less), you need to make sure the wires can handle the current and don't overheat-a potential fire hazard where the insulation of the wire could burn, etc... No current from the wires is used to run through the magnet. (Your magnet can be insulated, etc.) In reversing the direction of magnetism, the reversal would most likely take place within a few milliseconds, starting with a good permanent magnet, and a sufficiently strong magnetic field (from the solenoid) in the opposite direction.

 

[Part Toon]

Any solenoid you use to magnetize it must be insulated wire. You could do well to read about solenoids and magnetic fields=The field from the solenoid becomes stronger with stronger DC currents and also with more turns per unit length. When running high amounts of DC current through the solenoid (e.g. 1 or 2 amps or even less), you need to make sure the wires can handle the current and don't overheat-a potential fire hazard where the insulation of the wire could burn, etc... No current from the wires is used to run through the magnet. (Your magnet can be insulated, etc.) In reversing the direction of magnetism, the reversal would most likely take place within a few milliseconds, starting with a good permanent magnet, and a sufficiently strong magnetic field (from the solenoid) in the opposite direction.

I think I understand, but just in case, can you post a rough image?

I am pretty sure that somewhere on the farm, there's some insulated copper wire lying around.

 

[Charles Link]

I think I understand, but just in case, can you post a rough image?

I am pretty sure that somewhere on the farm, there's some insulated copper wire lying around.

For applying a magnetic field to a cylindrical magnet, you can just put the magnet inside the cylindrical solenoid. The magnetic field runs all throughout the inside of the solenoid in the direction of along its axis. The wire is wound many times around the solenoid, typically 20-30 loops or more per inch. For a washer/ring magnet, you would need to wind it (making the solenoid yourself), many times around through the middle and back to the outside, etc. For best results, you would want to wrap the entire donut/ring. For a probe wire, 5-10 loops might be sufficient, but for the magnetizing wire, (essentially a solenoid), i'd recommend about 100 loops if you can fit them all through the center. I can't supply a picture, but hopefully this helps... editing...Your ring magnet is essentially a long cylindrical magnet that is bent around in a loop so that the + and - poles make contact. You thereby need to have the solenoid be wrapped around as well. And additional comment on a previous item-in manufacturing a high-quality permanent magnet, I do think it is likely the magnetic field would be applied to the material when it is above the melting temperature, and not simply above the Curie temperature.

 

[Part Toon]

For applying a magnetic field to a cylindrical magnet, you can just put the magnet inside the cylindrical solenoid. The magnetic field runs all throughout the inside of the solenoid in the direction of along its axis. The wire is wound many times around the solenoid, typically 20-30 loops or more per inch. For a washer/ring magnet, you would need to wind it (making the solenoid yourself), many times around through the middle and back to the outside, etc. For best results, you would want to wrap the entire donut/ring. For a probe wire, 5-10 loops might be sufficient, but for the magnetizing wire, (essentially a solenoid), i'd recommend about 100 loops if you can fit them all through the center. I can't supply a picture, but hopefully this helps... editing...Your ring magnet is essentially a long cylindrical magnet that is bent around in a loop so that the + and - poles make contact. You thereby need to have the solenoid be wrapped around as well. And additional comment on a previous item-in manufacturing a high-quality permanent magnet, I do think it is likely the magnetic field would be applied to the material when it is above the melting temperature, and not simply above the Curie temperature.

Thanks, I think I'll try all of that stuff :D

But for a magnet about 2-3" in diameter, made out of ferrite, or iron, or something else, how much "juice" (electricity) would it take to re-magnetize it?