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A Permanently Magnetic Liquid

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127 pointsamingilani32 comments

"Before our study, people always assumed that permanent magnets could only be made from solids."

If you finely divide a magnet into tiny magnets and suspend these particles in a liquid, is that really a liquid magnet, or just a bunch of solid magnets floating in a liquid?

Technically, it is called a colloid. Like milk or blood.

https://en.wikipedia.org/wiki/Colloid

The physics-y way to answer this question is usually to define things in terms of the scales at which it's probed. If everything you can sense with macroscopic instruments is consistent with the liquid properties and the magnetic properties, it's a magnetic liquid. That it's "really" just solid magnets suspended in a liquid seems not much more relevant than the fact that solids are "really" fluids if you watch them on the astronomically long timescales on which they lose solid form due to tunneling.

In this case, it's a liquid magnet down to roughly the scales of the nanoparticles, which is only a bit bigger than the atomic scale on which nothing is a normal liquid.

The tunneling sounds interesting. Can you post a reference?

The example is from a Freeman Dyson paper, but I wouldn't take it too seriously.

https://physics.stackexchange.com/q/242654/7911

There are better example from condensed matter physics.

As I understand it (which, like most of the population of the planet, is not very much), solid magnets are also just a lot of smaller magnets floating in a macrostructure.

Permanent magnets are locked in place. If they're floating freely, the "tiny magnets" just snap together and cancel each other out. That's why heating (increasing particle mobility) a permanent magnet makes it lose its magnetization.

Not really floating, since that implies a certain freedom of movement that atoms in a solid don't have. But otherwise you are correct, since each electron is a tiny magnet (protons and neutrons are also magnets but their magnetic field strength is much smaller so they can safely be ignored). A macroscopic magnet is just a material where the electron magnetic fields add together to an macroscopically appreciable value, rather than cancelling each other out, i.e. the direction of the electron magnetic fields are largely aligned.

You've actually stumbled upon the central premise of this discovery.

If you finely divide a magnet into tiny magnets and suspend the particles in a liquid, you get... a normal ferrofluid. It's magnetic in the presence of an external field, but will lose its magnetization once that field is removed. This is because permanent magnetism (i.e. ferromagnetism) is a bulk property.

Every atom has a magnetic moment, but they are normally randomly aligned and thus the macroscopic field cancels out. It's only when these moments are aligned that a macroscopic magnetic field arises. Permanent magnets have the requisite crystalline structure for this to happen. As you chop it up, this macroscopic organization is destroyed.

If you get into the details, what they've done is to use the surface tension of the oil-in-water to "jam" an outer layer of magnetic particles and prevent them from rotating, thus preserving their magnetic alignment. This, in turn, is apparently enough to keep the free-floating, unjammed particles inside the droplet aligned as well, thus turning the entire droplet into a magnet. Pretty interesting, because without the membrane, none of the ferrofluid is magnetic, but with the membrane, all of it is.

So essentially they made small jelly (not really fluid) magnets out of ferrofluid.

> small jelly

More of a jam, since it contains solids. ;-)

PSA: Don't eat magnets more than one at a time.

This is a better explanation than the original article.

I second that

So is it just a single droplet? Seems to me that this would have to be useful for nano machine applications.

It's a magnet membrane surrounding a portion of liquid.

On one side your right, this isn't really a "liquid magnet", but on the other, this behaves like a magnet while retaining many of the properties of a liquid.

I think the question doesn't make sense, because if you take it further something interesting appears. If you do have tiny solid magnets in a liquid, why don't they rotate and cancel out?

They clearly cannot do so because macro sample would lose its properties. It simply cannot be tiny magnets suspended in a liquid. You gotta provide finer definition of a liquid because it typically does not have a structure. In your example there are constraints to movement and position of tiny magnets.

This may be useful in actually creating something I theorized about a few months ago. I call it a chemomagnet (as opposed to electromagnet).

The basic premise is that individual magnetic domains are free to float and are unorganized until a chemical signal locks them into place in some sort of structure. The energy required to align and bind them would be chemical in nature, and once bound, another chemical signal could be sent to unbind them.

The magnet would be controllable, like an electromagnet, but would not require any electricity at all to operate.

A bit like those heat packs where you click a metal disk inside them and they solidify, releasing heat? You could imagine doing the same but it 'turning on' a 'permanent' magnet.

Isn't a chemomagnet magnet just a scaled down version of a mechanical switchable magnet?

Yeah, but you could program it with any number and position of magnetic poles. Imagine a ring of this material as a stator in electric motor, you could reprogram it with 4 or 6 poles on the fly.

liquid programable motors with possible temporal formation capabilities! Sounds one step closer to Skynet's liquid metal terminator :-)

Fascinating!

I wonder if your idea - or this "magnetic liquid" - could have application in "artificial muscles"? Fascinating to think about...

Is it possible now to make a completely silent water/magnetic liquid cooler for a CPU by forcing this liquid to flow inside a heat pipe by a few electromagnets? Thus removing the noisy motor driven pump.

Great. Now we're one step closer to the T-1000.

Came to make the same comment.

I figure Skynet probably sent back an editorbot to flag your comment if you succeeded, but you tried your best to alter the future. John would be proud.

Nice and appropriate username ;-) Unfortunately it is not reddit here.

  And, even more curiously, the liquid can change shape - standing tall as a cylinder, flattening out like a pancake, round like a sphere, thinning out like a wire, or even more complex shapes, like… octopuses.

Yep I thought the same thing.

The T-1000 is one of the items on my "do not want" list.

What's interesting is that Arnold at first was unsure of the Terminator script ...

Arnold: "Ivan, this script ... is pretty weird ..."

Director Ivan Reitman: "Yeah, perfect for you."

After getting paid, Arnold bought an office building in LA. After a few more films and buildings, he was a billionaire, married into the Kennedy family, and became Governor of California, a stepping-stone to becoming President (had he been a born-American.)

It all started with a weird film script.

And back to the topic of materials, Arnold is literally a self-made man ... all of the Mr. Olympias trained themselves.

A little correction: Arnold was a real estate millionaire before he started doing movies. You can read/hear about it in the Tim Ferris Podcast/Tools of Titans book.

A big correction:

  Director Ivan Reitman

That director worked with Arnold on other movies, but isn’t associated with Orion or James Cameron or Dino De Laurentis, which was producing the Conan movies that Arnold was also working on at the time.

Ivan Reitman was doing comedies at the time (1984), and didn’t work with Arnold until 1988.

Considering Ivan Reitman shot his movies on location in New York, while James Cameron was producing his movies on the west coast, it’s fairly certain the entire comment is completely ficitious.

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