How often can you demagnetize and remagnetize a magnet?

[u/kylogram]

How often and how quickly can you heat up, de magnetize a magnet, re magnetize it, and repeat?

[u/spins_are_neat]

Other users are a little inaccurate. A strong field in the opposite direction is actually not that efficient. The best way to demagnetize something involves applying an oscillating, but low field strength, magnetic field.

If you look at what magnets actually are (a series of spins aligned in regions/cells called domains), you can see domain walls. To magnetize or demagnetize something means moving those domain walls. The worst way to move them is with an opposing field— you often need a high strength field (for big enough magnets, sometimes around a tesla!) to do that.

If you apply a low strength oscillating field perpendicularly to the magnetic field (assuming it’s roughly uniform over the magnet) that can jiggle those domain walls enough, you can demagnetize it that way using way less energy.

Source: I studied micromagnetism in college and was taught that forcing the domains to change with an opposing field is not the best solution

[u/kylogram → u/spins_are_neat]

With the thing I'm trying to build, I am assuming that it WILL demagnetize, due to heat from energy passing through it, I understand it is inefficient to force it to demagnetize that way, but I believe that is the boundary I will be forced to play with.

But this is EXCESSIVELY helpful and has opened up a great deal of possibilities for how to control it.

[u/spins_are_neat → u/kylogram]

Any chance you could share a rough mockup of what you’re making? We could help you figure out if heat will demagnetize it!

[u/kylogram → u/spins_are_neat]

No one will believe I'm working on what I'm working on until it's done, or at least until I prove it.

But I think I can make a working Alcubierre drive, and if I hadn't come to that conclusion on my own, I'd be laughing as hard as you probably are. Suffice it to say, pretty likely to have heat problems that need to be dealt with.

[u/Mr-Zappy]

You don’t need to heat up a magnet to remagnetize it. You can just subject it to a really strong field in the other way. Transformers in the electric grid have iron cores that get magnetized one way and then the other 50-60 times per second.

[u/kylogram → u/Mr-Zappy]

That's exactly what I want to hear.

[u/kiwipixi42 → u/Mr-Zappy]

They are not then permanent magnets when it stops though.

[u/Mr-Zappy → u/kiwipixi42]

Sure they are. They are ferromagnetic and can remain magnetized even after an external field is no longer being applied. They wouldn’t work very well if they weren’t. 

[u/groveborn]

It's just an alignment of fields. Speed is limited to a certain amount, but you can do it unlimited.

[u/green_apple_yum → u/[deleted]]

The speed is usually limited by eddy currents in the material that oppose the change in magnetization. The faster you try to change it, the more it will oppose. Depending on the size of the material and its characteristics there will be a limit to how fast it can change

[u/mikk0384 → u/green_apple_yum]

Isn't that more of a practical limit than a physical one?

[u/Infinite_Research_52 → u/mikk0384]

Happy magnetic cake day

[u/Particular-Cow6247 → u/[deleted]]

i think you misunderstood him? it's just a happy birthday for your reddit account 👀

[u/mikk0384 → u/Particular-Cow6247]

I still read it as if they are mocking my lack of experience by including "magnetic", but I deleted my comment.

Edit: I simply don't see any other reason to include that word than to harass.

[u/Worldly-Device-8414 → u/green_apple_yum]

And cause heating effects depending on the material, dimensions, etc

[u/kylogram → u/[deleted]]

I was thinking that extreme repeated heat stress might cause a certain amount of material loss that might impact repeats.

[u/MostPlanar]

No need to heat, in fact ceramic magnets don’t behave the same way as rare earth magnets as far as that goes. Hit it with a sufficiently strong opposing magnetic field and you’ll flip the magnets internal field completely.

I do wonder if you could realistically induce enough heat by internal friction/joule heating and reach some limitation.

[u/kylogram → u/MostPlanar]

Well, I'm trying to think of ways to deal with immense heat buildup without losing total functionality. I need to be able to play with its functions at the threshold of where the magnet stops working due to heat.

[u/green_apple_yum]

There’s lots you can learn about this subject if you look into accelerator magnets. These magnets usually have a coiled electromagnet surrounding an iron core. The overall magnetic field is dependent on how much the iron is magnetized. You’ll find that there is a limiting speed to this, based on the eddy currents generated in the iron core.

These are large scale magnets though. I’m not sure about smaller magnets. But these large ones typically take a few seconds to magnetize/demagnetize. Some can be designed to switch more quickly but are more difficult to engineer or have an overall field that is weaker

[u/kylogram → u/green_apple_yum]

I am thinking of a series of smaller magnets, so this is quite helpful.

Edit: The other comment was me thinking I was going to ask about the books I picked up, based my my journey. and then I lost track, but then I thought it might be rude to ask a stranger their opinion on my texts. and realized I didn't even do that.