How do you magnetize a circular magnet?

In summary: Can you tell me where I might be able to purchase something like that?In summary, a donut-shaped magnet with a hole in the center that the flux fields continuously circulate around is what the person is looking for. It is possible to convert a standard magnet into the desired shape by changing the direction of the magnetic domains. If the desired magnet is not available in this form, it may be possible to purchase one on eBay or at a hardware store.
  • #1
36
0
< Mentor Note -- thread moved from New Member Introduction Forum >

Hello, this is actually my first post on Physics Forums (I just joined)

The question above is the one that I thought that would grab the most attention.

I actually have 3 questions concerning magnets...

I require a special kind of magnet to complete my project, a magnet that the flux field lines continuously go around clockwise or counter-clockwise. Very similar to the magnets that were used in the REALLY old computers to store memory (I learned that in my set of old encyclopedias :D). I have a "donut" magnet that is the correct size and shape, except the flux lines act like a regular magnet (like a disc magnet with a hole in the center :P), in my project, this magnet is practically un-usable because of this (inconvenient) fact. I do not have such a magnet that the flux lines continuously go around, so I either need to make one or buy one :P

Question 1: What do you call such a magnet? I want to make sure that if I buy one, it is not like the one that I already have :P

Question 2: Is it possible to convert the magnet that I have now into the magnet that I need (by changing the direction of the magnetic domains)? By doing some sort of electro-magnet thingy to switch the direction of the field?

Question 3: If I can't make one, where would I be able to purchase such a magnet with the clockwise or counter-clockwise field, and not simply a regular field? I'd prefer it'd be some sort of store that I can examine the magnet in person before purchase (i.e. not on the internet). Maybe Menards or Staples, but I don't have a way to go from place to place, so I'd prefer to know exactly where I can get it before I drive my Mom crazy going from place to place :P

Remember, the magnet I need MUST have a clockwise or counter-clockwise field.

Thanks :)
 
Last edited by a moderator:
Physics news on Phys.org
  • #2
Part Toon said:
I require a special kind of magnet to complete my project, a magnet that the flux field lines continuously go around clockwise or counter-clockwise. Very similar to the magnets that were used in the REALLY old computers to store memory
What size donut are you talking about? Do you need it as a permanent magnet?

I haven't tried this, but I imagine you could magnetise two semicircular pieces of suitable material then tape or glue them together to form the complete circle. Picture semicircular horse-shoe magnets, maybe they can be purchased in that very shape?

If you can get hold of a toroid (ring-shaped) piece of suitable unmagnetised material you'll probably find it can be neatly sawn in half with a fine hacksaw.

The computer memory used solenoids around the core to magnetise it; tiny ferrite cores with fine wires.

How are you going to make use of the magnet?
 
  • #3
Search for Core Memory on ebay. Prices range from $3 for 500 bare cores to $2000 for a large rackmount assembly.

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=core+memory&rt=nc

Or if you want a larger one, get a large nut from the local hardware store. To magnetize it you can wrap small, well insulated, wire thru the hole (as many turns as will fit) then momentarily connect the coils ends to a "D" cell flashlight battery. The wire will get hot so don't leave it connected very for long!
 
  • #4
Tom.G said:
Search for Core Memory on ebay. Prices range from $3 for 500 bare cores to $2000 for a large rackmount assembly.

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=core+memory&rt=nc

Or if you want a larger one, get a large nut from the local hardware store. To magnetize it you can wrap small, well insulated, wire thru the hole (as many turns as will fit) then momentarily connect the coils ends to a "D" cell flashlight battery. The wire will get hot so don't leave it connected very for long!
That might work, the magnet that I need must have a "donut" hole that is at least 1.5" across. It *must* be a permanent magnet, an electro magnet wouldn't work :P

I don't think what NascentOxygen said about the semi-circle thing would work for me, the issue I have with this magnet to begin with is that it has to be a single piece. If it is multiple, it has a higher chance of having exposed North and South poles, my entire goal (as for this magnet) in my project is to obtain a circular magnet, that is a single piece so that it will not have poles. I think I may have forgotten a few details in my first post :P I might be able to make a miniature version of my device using those "Core Memory" thingies that you were mentioning :)

To conclude (for now), I require a permanent magnet, that is large enough to do stuff with (like put another setup of magnets inside), and has a circular magnetic field (clockwise or counter-clockwise)
 
  • #5
Can you start with a bar magnet, drill a hole in it, then machine it to the donut shape?
 
  • #6
NascentOxygen said:
What size donut are you talking about? Do you need it as a permanent magnet?

I haven't tried this, but I imagine you could magnetise two semicircular pieces of suitable material then tape or glue them together to form the complete circle. Picture semicircular horse-shoe magnets, maybe they can be purchased in that very shape?

If you can get hold of a toroid (ring-shaped) piece of suitable unmagnetised material you'll probably find it can be neatly sawn in half with a fine hacksaw.

The computer memory used solenoids around the core to magnetise it; tiny ferrite cores with fine wires.

How are you going to make use of the magnet?

So...

(20 seconds after other post :P)

I looked up the stuff about core memory stuff, and that stuff looks pretty cool :) I think I know what to call the magnet now: "Big ferrite core". But yes, I still need it to be a few inches in diameter.

Sorry anorlunda :P I cannot do that, I need the magnet to have a circular field along with a circular shape :P

Keep replying please, I might need more info on the stuff :D

EDIT: I did an Ebay search for "Big ferrite core" and I got this...

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

You guys may want to take a look at this, and maybe give me your opinions on whether it has a circular magnetic field or not :D
 
  • #7
Ferrite is the core for an electromagnet, so is not what you seek.

I doubt that you will get a permanent magnet donut, because with no exterior field it would have no uses. I think 2 semicircular horse-shoe magnets would produce what you are asking for. Whether it will achieve the feats you're planning is quite another matter.
 
  • #8
NascentOxygen said:
Ferrite is the core for an electromagnet, so is not what you seek.

I doubt that you will get a permanent magnet donut, because with no exterior field it would have no uses. I think 2 semicircular horse-shoe magnets would produce what you are asking for. Whether it will achieve the feats you're planning is quite another matter.
Well, ferrite is like a ceramic magnet material, nearly every permanent magnet that I have is made of the stuff, very handy. I do in fact need a donut permanent magnet, it has, special uses...

The Ebay post has a 30 day back thingy, so if it is not what I'm looking for, I can simply return it.

Please don't stop giving me free-info about the stuff, I never know when I might need some good-old knowledge to use for my secret project :)
 
  • #9
That's true, fridge magnets being a good example. But if it's sold as a ferrite core then it's almost certainly a soft ferrite for a transformer or electromagnet. If it was a ferrite toroid for a permanent magnet then it would be sold already a magnet. There would be no market for the item you seek because it sounds like something of almost no practical value---at least, not until it's broken.

Does it need to be both circular and of round cross-section? Otherwise, you could readily get hold of a pair of squarish horseshoe magnets and join them into a neat rectangle with rounded corners.
 
  • Like
Likes davenn
  • #10
Part Toon said:
The Ebay post has a 30 day back thingy, so if it is not what I'm looking for, I can simply return it.

again, it isn't what you seek, don't waste your time and moneythe only donut shaped magnets, that I know of, and of the size you require, are in loud speakers
every modern speaker has one, I have even dismantled a few blown speakers over the years and removed the magnetsDave
 
  • #11
NascentOxygen said:
That's true, fridge magnets being a good example. But if it's sold as a ferrite core then it's almost certainly a soft ferrite for a transformer or electromagnet. If it was a ferrite toroid for a permanent magnet then it would be sold already a magnet. There would be no market for the item you seek because it sounds like something of almost no practical value---at least, not until it's broken.

Does it need to be both circular and of round cross-section? Otherwise, you could readily get hold of a pair of squarish horseshoe magnets and join them into a neat rectangle with rounded corners.

Well, let me redefine the magnet I need, it has to be a toroid circular donut-shaped magnet, that is a single piece, that does not contain any creases or weld/glue points :P But most importantly, it must have either a clockwise or counter-clockwise magnetic field, and it must be a permanent magnet, an electromagnet simply couldn't work for my uses :P

I could check out the ones found in speakers, there's probably an old-junky speaker lying around somewhere on the farm that I live on, I could dismantle it, and see if the magnet will work for my project :D

But the magnet I require is in no way useless, I have done some experiments with several 1 7/8" x 7/8" x 3/8" ceramic ferrite magnets, 24 of them to be exact. I assembled them into a ring (North pole touching South pole of the next magnet) to see if it would work for my project. Unfortunately, some of the magnets were slightly more powerful than the others, and they weren't all perfectly aligned, so that created set North and South poles, so I need it to be as a single piece. And with a circular magnetic field (I tend to call circular magnetic fields "Flux Rings").

Please keep replying, I may need some more info on the stuff :)
 
  • #12
davenn said:
the only donut shaped magnets, that I know of, and of the size you require, are in loud speakers

Those are plentiful and cheap.
speaker magnets 1.75" - 10 each for $10
http://www.ebay.com/itm/speaker-magnets-1-75-10-each-/281991060257?hash=item41a7fa1b21:g:n-8AAOSwp5JWW2v8
 
  • Like
Likes davenn
  • #13
So you want a permanent magnet like this:
toroid.png

only without the wire?

I don't think anyone makes such a thing. As NascentOxygen says:

NascentOxygen said:
...There would be no market for the item you seek because it sounds like something of almost no practical value---at least, not until it's broken.

There was no market for such a thing, until you showed up.
Testing to see whether or not it had a permanent magnetic field might make a good homework problem.
I guess you could set it up like the magnetic-core memory, from your original post, and have a single bit place to store all your information.

ps. I think a large flat washer will work. Appropriate material of course.
 
  • #14
OmCheeto said:
I don't think anyone makes such a thing.
OmCheeto said:
There was no market for such a thing, until you showed up.

see my post :wink:
they are plentiful

Dave
 
  • #15
davenn said:
see my post :wink:
they are plentiful

Dave
But the magnetic flux field is not as requested.

Part Toon said:
I require a special kind of magnet to complete my project, a magnet that the flux field lines continuously go around clockwise or counter-clockwise. Very similar to the magnets that were used in the REALLY old computers to store memory

Unless of course, you have really weird speakers down under.

Here is a picture of one of my old speaker magnets, with the poles annotated.

speaker.magnet.field.png


The sewing needle is suspended in air, and is pointing to the strongest part of the south pole.
The north pole is strongest in the center of the top.
The poles may have shifted, from what was originally designed, as the space around the central magnet is now filled with iron filings.

(I used this magnet to look for my keys one day, 10 years ago, underneath 20 feet of water. I found my chair. [ref] I eventually found my keys, 3 months later.:partytime: One of these days, I'll finish that story. :redface: )
 
  • Like
Likes Tom.G
  • #16
It appears that there are a lot of ideas for what I need, I decided to make a .png image to demonstrate...

https://physicsforums-bernhardtmediall.netdna-ssl.com/data/attachments/84/84646-5270c0cfad4a3b7d3ad8d72f7e935d59.jpg [Broken]

(it may look a little cheap, I assembled it in a couple of minutes :P)

EDIT: I just realized how small the image is :P You may need to download the image by dragging it to your desktop to see the details :P

This is the kind of magnet that I need, it must be a permanent magnet, that is all a single piece. I simply cannot use multiple magnets that were attached together :P

So... would any of you know what this sort of thing is called? And how I could either make or purchase one? Maybe a specific Ebay post, or a store that carries a wide variety of magnets? Or I might be able to create one if I knew how...

P.S. The magnet must also be a few inches in diameter.

Please continue to post more stuff about your experiences with magnets, it's really helpful :D
 

Attachments

  • Magnet picture.png
    Magnet picture.png
    3.4 KB · Views: 898
Last edited by a moderator:
  • #17
going on from Om's comment about my speaker magnet idea

if that doesn't fit your criteria, I'm starting to pick that you are not likely to find one with the magnetic properties you state
 
  • #18
davenn said:
going on from Om's comment about my speaker magnet idea

if that doesn't fit your criteria, I'm starting to pick that you are not likely to find one with the magnetic properties you state

I may be able to try the speaker thing some time soon, but so far, I haven't had enough time to do that :P I have a question, the magnets used in old computers (core memory as I heard it is called), aren't they simply miniature versions of what I need?
 
  • #19
Part Toon said:
I have a question, the magnets used in old computers (core memory as I heard it is called), aren't they simply miniature versions of what I need?

they were not magnets, they were ferrite cores that would be magnetised with the data signal passing through them on a wire
and in general they were tiny ... I used to have a chunk of core memory, the cores were a couple of mm in diameter

CoreMemory.jpg


navy-core-memory-fig-6-03.gif


https://en.wikipedia.org/wiki/Magnetic-core_memoryDave
 
  • #20
@OmCheeto mentioned a flat washer. Could you permanently magnetized one with a coil, then remove the coil?
 
  • #21
davenn said:
they were not magnets, they were ferrite cores that would be magnetised with the data signal passing through them on a wire and in general they were tiny ... I used to have a chunk of core memory, the cores were a couple of mm in diameter

I do know that ferrite is a material that has the ability to become a permanent magnet, most of my magnets are made of ferrite. So do you think I might possibly be able to magnetize a piece of non-magnet ferrite (or any piece of material that can become a permanent magnet) into the way that I require, by doing the same thing that the core memory thinga-ma-doodles did?
 
  • #22
If you want a strong field I would recommend a neodymium magnet.
You can just get yourself a ring shaped magnet and remove it's magnetization by heating it above it's curie temperature e.g. with a blowtorch.
Then you magnetize it again with a coil of insulated wire wrapped around it.
In this video - starting at 10:00 min - you can see how this is done in a factory with coils of wire and a capacitor to achieve very high currents.

But I wonder why you won't tell us what you need this for. It doesn't have anything to do with violating the laws of physics, does it?
 
  • Like
Likes Part Toon
  • #23
What about using a series of wedge shaped magnets :
upload_2016-6-3_10-36-58.png

Their North-South poles can be oriented on the sides so that the fields rotate as required, and the equivalent of a flat iron washer can be placed on either side to link the fields. What you then have (and must end up with based on your diagram) is an alternating North-South set of poles (much like in a linear accelerator) around the circumference.
 
  • #24
DrZoidberg said:
If you want a strong field I would recommend a neodymium magnet.
You can just get yourself a ring shaped magnet and remove it's magnetization by heating it above it's curie temperature e.g. with a blowtorch.
Then you magnetize it again with a coil of insulated wire wrapped around it.
In this video - starting at 10:00 min - you can see how this is done in a factory with coils of wire and a capacitor to achieve very high currents.

But I wonder why you won't tell us what you need this for. It doesn't have anything to do with violating the laws of physics, does it?

I like your idea :D I think I should try that. It'll take some research on the correct material to use, and what it's curie temperature is, but after that, I think I give it a shot.

But what Allan just said about the wedges, I have tried something similar to that. I used 24 magnets all put together to make a ring, however, there were imperfections within it, for it was not all a single piece. There were exposed North and South poles :P It simply could not work for me in my case.

As for my purpose of why I need such a magnet...

It is a secret, I simply cannot tell you what my project is at this time. I can tell you that it is not something harmful, it will actually help mankind to the highest of possible benefits. About 3 years ago, when I started on this project, I didn't have a clue about the true nature of magnetism :P After 3 years of experimenting, I'm getting very close to completion :)

P.S. God has commanded me to construct this machine a while ago, I must complete it. With His help (and yours of course), I can make this possible.

Please continue to reply, you guys have helped me out a lot so far :D
 
  • #25
Part Toon said:
I can tell you that it is not something harmful, it will actually help mankind to the highest of possible benefits. About 3 years ago, when I started on this project, I didn't have a clue about the true nature of magnetism :P After 3 years of experimenting, I'm getting very close to completion :)

P.S. God has commanded me to construct this machine a while ago, I must complete it. With His help (and yours of course), I can make this possible.
So violating the laws of physics it is then.
I just hope you are not too disappointed when you find that it doesn't work.
 
  • Like
Likes davenn and DrewD
  • #26
DrZoidberg said:
So violating the laws of physics it is then.
I just hope you are not too disappointed when you find that it doesn't work.

No, not really. I have tried and tried over and over again to try to get it to work, but just like Thomas Edison said:

"I didn't fail, I just found 10,000 ways how not to make a light bulb, but I only needed one way to make it work."

Remember, failing does not make you a failure, but giving up after you fail makes you a failure.

I have formulated why what I am doing might be possible, can't hurt to try. Simply because people throughout the past have tried and failed, does not mean it's impossible.

Each time that I have tried, I thought that it would work (because if I didn't, I wouldn't try). When it doesn't work, I take a break, find out what's wrong, think about it, formulate a possible solution, and then repeat the process.
 
  • #27
Fine, good luck to you then.
But please try not to electrocute yourself on your holy mission.
It's probably best if you don't use voltages above 30V in any of your experiments. You can get enough current flowing through the coil with a low voltage.
 
  • Like
Likes Part Toon
  • #28
DrZoidberg said:
Fine, good luck to you then.
But please try not to electrocute yourself on your holy mission.
It's probably best if you don't use voltages above 30V in any of your experiments. You can get enough current flowing through the coil with a low voltage.

Yeah, it'd probably be bad if I electrocute myself :P (It'd be a funny story to tell though XD)

I can probably do some more testing with the info that I have now, but I may have to return for more magnet information eventually :D

Thanks for the help :D

But please expect a near-future reply on the subject, because if my test doesn't work, then I'll most likely return here and continue this discussion :)
 
  • #29
Ferrite is a ferromagnetic material (high permeability) with low retentivity, ground into a powder and mixed with an insulating ceramic binder (glue) to reduce eddy currents that create losses at radio frequencies. It would make a poor permanent magnet. For good performace you want a ferromagnetic material with high retentivity (i.e. retains significant magnetization after you remove the magnetizing field).
 
  • #30
David Lewis said:
Ferrite is a ferromagnetic material (high permeability) with low retentivity, ground into a powder and mixed with an insulating ceramic binder (glue) to reduce eddy currents that create losses at radio frequencies. It would make a poor permanent magnet. For good performace you want a ferromagnetic material with high retentivity (i.e. retains significant magnetization after you remove the magnetizing field).

A material like neodymium?

I have roughly 100 tiny disk magnets made out of neodymium, they are incredibly strong for there small size O_O
 
  • #31
Yes. Sintered NdFeB has the highest energy density.
 
  • #32
David Lewis said:
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 :smile:
 
  • #33
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.
 
  • #34
NascentOxygen said:
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 :smile:
 
  • #35
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.
 

Suggested for: How do you magnetize a circular magnet?

Replies
11
Views
564
Replies
10
Views
483
Replies
1
Views
799
Replies
7
Views
1K
Replies
198
Views
8K
Replies
1
Views
778
Back
Top