How do you magnetize a circular magnet?

[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?

 

[Charles Link]

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?

I think that depends very much on the type and condition of the material-you may or may not be able to remagnetize it permanently. Most likely you could make an electromagnet out of it, but the magnetization might not persist upon removal of the (solenoid) field.

 

[Part Toon]

I think that depends very much on the type and condition of the material-you may or may not be able to remagnetize it permanently. Most likely you could make an electromagnet out of it, but the magnetization might not persist upon removal of the (solenoid) field.

Well, hopefully it does :)

I could try different materials until I find the correct one :)

Preferably materials that are already magnets :P

 

[Charles Link]

One suggestion I have for you if you want to do in-depth experiments with magnetic rings: Start first with cylindrical magnets of various materials using a cylindrical solenoid. You can even wrap a couple of loops for a probe around the cylindrical sample. It would be much easier to make your observations both by observing the magnetic field outside the cylindrical magnet: Did the poles get reversed?, etc...and comparing to what type of signal you got on an oscilloscope. It is much more difficult to work with rings where you need to hand-wrap every ring and you don't get any appreciable field external to the ring to tell you what is going on inside of it.

 

[Part Toon]

One suggestion I have for you if you want to do in-depth experiments with magnetic rings: Start first with cylindrical magnets of various materials using a cylindrical solenoid. You can even wrap a couple of loops for a probe around the cylindrical sample. It would be much easier to make your observations both by observing the magnetic field outside the cylindrical magnet: Did the poles get reversed?, etc...and comparing to what type of signal you got on an oscilloscope. It is much more difficult to work with rings where you need to hand-wrap every ring and you don't get any appreciable field external to the ring to tell you what is going on inside of it.

I like your idea

When I get to the point to test different materials, I shall do the cylinder thingy that you mentioned

My plan...

1. Get a bunch of cylinder magnets of various ferromagnetic materials

2. Test them with solenoids, to find a good ratio of wire-magnet-electricity input

3. Once I find one, obtain a ring of such a material, and then repeat the process with the solenoid

4. Assemble my secret device using my new circular magnet

5. If my secret device finally works this time, after 3 years of working, then I shall begin the next phase of my plan, P.I. (not private investigation if you are wondering)

6. After P.I. is complete, then I'll do a bunch of other stuff that I'll make up as I go :P

 

[Part Toon]

65 posts already!

I never expected this many on my simple questions! :P

 

[Charles Link]

I did a google of the topic "reversing the polarity of a permanent magnet" and the answer was very much what I expected. (You might find it worthwhile to google this as well.) For a high quality permanent magnet, it takes a considerable amount of reverse current in the solenoid (for a very brief time). The alternative method of heating above the Curie temperature and applying a reverse magnetic field as it cools doesn't require anywhere near the magnetic field strength in the solenoid that is required for the first case. The magnetic field strength in the first case might be difficult to achieve.

 

[NascentOxygen]

Poster is not seeking to reverse the polarity of a magnet.

The major feat here, if achievable, is to permanently remove all evidence of a magnet ever having been magnetised in a radial direction.

Magnetising it circumferentially will be a cinch, in comparison.

 

[Part Toon]

Actually, the goal is to magnetize a magnet by changing the direction of the magnetic domains. Not to reverse them, or remove them, but altering their direction into a clockwise or counter-clockwise manner.

 

[anorlunda]

Can't you take a bar magnet, bend it into a circle, then spot weld the ends together?

The welding might demagnetize only a small portion of the bar.

 

[my2cts]

I found this instruction on the web for magnetising materials: http://oersted.com/magnetizing.PDF
The sketch in post #13 gives the geometry for your specific case: wind a solenoid around the doughnut.

 

[Charles Link]

The "link" that my2cts provides is interesting. It also details the difficulty of creating the magnetic fields $B$ in excess of $B= 1 weber/m^2$ that would be necessary to change the direction of magnetism of a permanent magnet.

 

[Part Toon]

Recently, I was experimenting with a nail, a solenoid made from some sort of TV wire (I think), and a transformer for the 12V input. After a few tries, I made an electromagnet

With this new knowledge about electromagnets, I have decided to purchase 2x 50-foot long extension cords (I looked, and some are $10 each ), FYI: I have not yet purchased the extension cords. After that, I will disassemble the cords, and pull out the insulated wires that lie within. Then I shall construct a rig to support the "Chuck magnet" mentioned earlier, then I'll wrap the magnet until I run out of wire. I will carefully place the magnet & solenoid into my rig, then I'll attach the wires into a light socket (carefully and precisely) to get 120V rather than a little 12V

Hopefully, after a second or 2 in the rig, it'll be re-magnetized into the form that I require for my secret project

 

[Charles Link]

Recently, I was experimenting with a nail, a solenoid made from some sort of TV wire (I think), and a transformer for the 12V input. After a few tries, I made an electromagnet

With this new knowledge about electromagnets, I have decided to purchase 2x 50-foot long extension cords (I looked, and some are $10 each ), FYI: I have not yet purchased the extension cords. After that, I will disassemble the cords, and pull out the insulated wires that lie within. Then I shall construct a rig to support the "Chuck magnet" mentioned earlier, then I'll wrap the magnet until I run out of wire. I will carefully place the magnet & solenoid into my rig, then I'll attach the wires into a light socket (carefully and precisely) to get 120V rather than a little 12V

Hopefully, after a second or 2 in the rig, it'll be re-magnetized into the form that I require for my secret project

Don't use a light socket for voltage-it is AC(alternating current). That means the voltage is $V=V_o \cos(\omega t)$ where $\omega=2 \pi f$ and $f=60 Hz$ . If you didn't follow the mathematics, it means the polarity of the light socket voltage switches rapidly back and forth (60 cycles each second). Your 12 volts DC (direct current) should work well. You are more limited by available current than voltage. I would even recommend placing a resistor R=10 ohms that is rated at 1 watt in series in your solenoid circuit so that you don't drain the battery too quickly. You should at least be able to make an electromagnet from your previous magnet that has lost its magnetism. You may or may not be able to make it back into a high quality permanent magnet.

 

[Part Toon]

Don't use a light socket for voltage-it is AC(alternating current). That means the voltage is $V=V_o \cos(\omega t)$ where $\omega=2 \pi f$ and $f=60 Hz$ . If you didn't follow the mathematics, it means the polarity of the light socket voltage switches rapidly back and forth (60 cycles each second). Your 12 volts DC (direct current) should work well. You are more limited by available current than voltage. I would even recommend placing a resistor R=10 ohms that is rated at 1 watt in series in your solenoid circuit so that you don't drain the battery too quickly. You should at least be able to make an electromagnet from your previous magnet that has lost its magnetism. You may or may not be able to make it back into a high quality permanent magnet.

Thanks for that

Are you sure just 12 volts would work? I do agree with the AC-DC thing, but I may need more voltage, but I don't know for sure :P

So maybe instead of the light socket, I should use the DC transformer I mentioned earlier?

 

[Charles Link]

Thanks for that

Are you sure just 12 volts would work? I do agree with the AC-DC thing, but I may need more voltage, but I don't know for sure :P

So maybe instead of the light socket, I should use the DC transformer I mentioned earlier?

Your solenoid has very low electrical resistance=most likely less than 1 ohm. You could easily drain a 12 volt battery in a minute or two without any additional resistor in the circuit. It is electrical current that makes your solenoid work, but if you have enough loops, you can reduce the current. A 10 ohm resistor would make the current be about 1 amp. That is more than enough to get a good magnetic field if you have enough loops(turns) in your solenoid. Yes, a DC transformer would also work=and you save on money by not needing to purchase batteries. A DC transformer that can deliver high currents (.5 -1.0 amps at 12 volts DC would be helpful and again use a R=10 ohm resistor (rated at 1 watt or more). Without the resistor, you might burn out the DC transformer. Be sure your resistor can handle the power also=(1 watt or more). You can even touch your finger to the body of the resistor and make sure it isn't getting too warm...=be a little careful when connecting circuits like this=components can get hot on occasion and smoke, etc.

 

[Part Toon]

Your solenoid has very low electrical resistance=most likely less than 1 ohm. You could easily drain a 12 volt battery in a minute or two without any additional resistor in the circuit. It is electrical current that makes your solenoid work, but if you have enough loops, you can reduce the current. A 10 ohm resistor would make the current be about 1 amp. That is more than enough to get a good magnetic field if you have enough loops(turns) in your solenoid. Yes, a DC transformer would also work=and you save on money by not needing to purchase batteries. A DC transformer that can deliver high currents (.5 -1.0 amps at 12 volts DC would be helpful and again use a R=10 ohm resistor (rated at 1 watt or more). Without the resistor, you might burn out the DC transformer. Be sure your resistor can handle the power also=(1 watt or more). You can even touch your finger to the body of the resistor and make sure it isn't getting too warm...

Yeah, I can do that.

(I already have a DC transformer that plugs into the wall, so that'll save a lot of time)

This means the last piece of the puzzle is to buy the 2x 50-foot extension cords for about $20 :D

And of course, a bunch of assembly that'll probably take a few hours :P

 

[Charles Link]

Yeah, I can do that.

(I already have a DC transformer that plugs into the wall, so that'll save a lot of time)

This means the last piece of the puzzle is to buy the 2x 50-foot extension cords for about $20 :D

And of course, a bunch of assembly that'll probably take a few hours :P

I edited my post #75. Please read the last couple of sentences to be somewhat careful. Sounds like a fun experiment !

 

[Part Toon]

I edited my post #75. Please read the last couple of sentences to be somewhat careful. Sounds like a fun experiment !

So yes, I shall continue to reply after I purchase the extension cords, assemble the magnetizing device, and test the magnet, and then assemble my secret machine.

When I'm done magnetizing stuff, I'll reply telling you how it went :D

 

[RMN]

What you are needing cannot be accomplished except by an electromagnet - - - or a permanent magnet array - - - - - composed of many magnet segments, such as a Halbach array, although in your case all the segments would follow in the same direction, head to tail.

 

[Part Toon]

What you are needing cannot be accomplished except by an electromagnet - - - or a permanent magnet array - - - - - composed of many magnet segments, such as a Halbach array, although in your case all the segments would follow in the same direction, head to tail.

Why do you think a permanent magnet cannot be like this? With the round field and all?

 

[Charles Link]

Why do you think a permanent magnet cannot be like this? With the round field and all?

Just one additional comment on your closed magnetic rings=it doesn't seem to leave any method to probe the magnetism inside the ring. It is also possible to make a magnetic ring/permanent magnet that has a small air gap in the ring. The magnetic field $B$ will pass continuously across the air gap. This would allow you to probe the $B$ in the air gap with a loop of current-carrying wire, etc.

 

[Part Toon]

Just one additional comment on your closed magnetic rings=it doesn't seem to leave any method to probe the magnetism inside the ring. It is also possible to make a magnetic ring/permanent magnet that has a small air gap in the ring. The magnetic field $B$ will pass continuously across the air gap. This would allow you to probe the $B$ in the air gap with a loop of current-carrying wire, etc.

So... possible? :D

FYI: I don't need that much of the flux to escape the magnet, just a little tiny bit.

 

[D2Bwrong]

Magnetism has a directional orientation. The field will be generated strongest parallel to the orientation of the NS poles.
You might want to try this. Take a flat magnet and cut out a circular section. Drill a hole in the circular section. Cut another piece in the magnet to fit the hole. Determine the orientation of the two circular pieces then place the smaller piece in the hole with the 2 north and east directions pointed in opposite directions. This should produce a toroidal effect. If that's isn't what you were looking for try placing the small piece inside the hole with the north and east poles oriented in their correct orientations ( you may have to use a device to keep it from spinning). This may nullify the field lines passing through the center.

 

[Part Toon]

Magnetism has a directional orientation. The field will be generated strongest parallel to the orientation of the NS poles.
You might want to try this. Take a flat magnet and cut out a circular section. Drill a hole in the circular section. Cut another piece in the magnet to fit the hole. Determine the orientation of the two circular pieces then place the smaller piece in the hole with the 2 north and east directions pointed in opposite directions. This should produce a toroidal effect. If that's isn't what you were looking for try placing the small piece inside the hole with the north and east poles oriented in their correct orientations ( you may have to use a device to keep it from spinning). This may nullify the field lines passing through the center.

I don't think you quite understand what I am going to do, I'm going to use a solenoid made from wires from an extension cord. I'm not going to use the Earth's North and South poles to magnetize my circular magnet, but instead, a very powerful solenoid wrapped around it.

 

[Charles Link]

I don't think you quite understand what I am going to do, I'm going to use a solenoid made from wires from an extension cord. I'm not going to use the Earth's North and South poles to magnetize my circular magnet, but instead, a very powerful solenoid wrapped around it.

Recommend getting insulated wire of a moderate gauge-don't use an extension cord=the insulation is too thick and will limit how many turns you can make. You can get 100 ft. of insulated wire on a spool for perhaps $5=from Radio Shack. You don't need tremendously thick insulation.

 

[Part Toon]

Recommend getting insulated wire of a moderate gauge-don't use an extension cord=the insulation is too thick and will limit how many turns you can make. You can get 100 ft. of insulated wire on a spool for perhaps $5=from Radio Shack. You don't need tremendously thick insulation.

Thanks for the tip

Instead of buying a 100 ft. extension cord, I shall instead purchase 2 or 3 of those insulated wire spools that you spoke of, how would one word that while looking for it on their website?

 

[Tom.G]

Hook-up wire.

 

[Part Toon]

Hook-up wire.

Danke schön

(Thank you in German)

 

[Tom.G]

ఆసక్తి దాయకంగా ఉంటాయి
(phonetically: Āsakti dāyakaṅgā uṇṭāyi)

(You are welcome in Telugu)
(Google Translate is great. I don't even know where Telugu is spoken!)

 

[Part Toon]

ఆసక్తి దాయకంగా ఉంటాయి
(phonetically: Āsakti dāyakaṅgā uṇṭāyi)

(You are welcome in Telugu)
(Google Translate is great. I don't even know where Telugu is spoken!)

There's been a change in plans...

A while ago, I helped my Grandma by shoveling some mud out of her basement after it got flooded :P She gave me 2x 25 foot old extension cords. I took apart one for the wire inside for my experiments, turns out, the wire works great, the insulation isn't too thick :D

I have discovered that a circular solenoid doesn't work the way I was hoping, so instead, I have decided to do it the same way that the core-memory things do, have a bunch of wires go through the center of a ring magnet, making sure that the electricity is flowing all the same directions :P And then maybe hitting the magnet with a hammer a few times to re-position all of the domains :P

I have done a test with a piece of ring-shaped metal, and guess what? It works!

So after I get a new ring magnet to use (the hole on the "Chuck" magnet is too small), then I can continue with my experiments, and I can finally complete my secret device

 

[Charles Link]

Glad you found something that works. Perhaps there is a textbook/handbook out there that discusses magnetic engineering in simple terms and shows a lot of practical applications. Besides the high quality permanent magnets that would require fields much stronger than what can easily be created in a solenoid to reverse the permanent magnetization, there are no doubt materials available that make low quality permanent magnets where the field strength is somewhat weak but also makes for a permanent magnetism whose direction can be reversed without requiring enormously strong reverse magnetic fields.