The article's title is misleading: they actually mean a new kind of permanent magnet (that was theoretically predicted but hadn't been observed until now), not a new kind of magnetism (as in, something not predicted or accounted for by our existing theory of electromagnetism).
As a condensed matter physicist (working in the same field but not on altermagnetism specifically), I would say this is being much more picky about the language than most people in the field tend to be. Moreover, I'm not sure you're even right about the language.
You are correct that this doesn't involve any changes to our understanding of electromagnetism in general; whether or not that means that altermagnetism is not a new type of magnetism is a matter of semantics. If I read in a paper or heard in a seminar that "altermagnetism is a new type of magnetism", I would not quibble with the language, though that phrase by itsself is almost tautologically pointless.
If you want a more technically meaningful phrase, I would propose that altermagnetism is a newly-discoved "magnetically ordered phase". Of course that doesn't fit so well in a headline.
> I would say this is being much more picky about the language than most people in the field tend to be.
Perhaps, but I think that when communicating with the public (as opposed to communicating with other physicists), "a new kind of magnetism" suggests something that isn't explained by our current theories, not just something that our existing theories predict but hadn't been observed before.
As someone who isn't a physicist, headlines like this make me think they discovered magnets that work with some non-ferrous material, which would be amazing. But then I was like "wouldn't that be crazy" and then came to the comments specifically to see what the actual explanation would be.
Sounds like shorthand terminology in your subfield is okay with the usage of "magnetism." But that's local slang, as a (former) high energy theorist I interpret the phrase "a new form of magnetism" as a new gauge theory or something equally spectacular. So I just rolled my eyes at the headline.
It's a new kind of magnetic medium that had not been previously observed. It is not something that can't be explained by our existing theory of electromagnetism.
> I am not sure it can be called a magnet.
It's an object that has magnetic properties. That's a magnet. It's a different kind of magnet from those we had previously observed.
> Each magnetic medium exhibits its own kind of magnetism.
I agree that it is sometimes described this way, although as one commenter upthread said, such use of language is more common when physicists are talking among themselves, not when they are talking to the public.
The comments in this discussion indicate that I am by no means the only one who was confused by the original wording. So I think the change was helpful.
Monopoles are already accounted for though, because they’re explicitly ruled out by the character and form of the laws of electromagnetism. ∇⋅B = 0, or “the divergence of the magnetic field is zero”.
When Maxwell first published his work with the equations, it contained non-zero B divergence. We say that density of magnetic monopole (which should be there instead of zero) is zero because we did not find any monopoles yet (maybe ever!). If we discover a monopole, and we remove this zero, there will no problems with EM theory, and actually we can explain some other things like quantization of electric charge (why all charge are integer multiple of electron charge).
So no, it was not explicitly ruled out by Maxwell's equations. It is not even ruled out because we did not explore the full phase space. And it depends on which monopole you are talking about (Dirac monopole, GUT monopole or EW monopole).
I mean I we found a magnetic monopole then we'd just change that one of Maxwell's equations so it looks like the corresponding electrical equation Div(E) = ρ/ε. It essentially just happens that the thing which correspond to ρ for the B field is 0.
Except that if the divergence of the magnetic field were anything other than zero, the laws as presently written wouldn’t successfully predict electromagnetic effects. Because the laws as currently written _do_ make predictions, and exquisitely precise predictions at that, the divergence must be zero with no monopoles at all or so close to zero that monopoles would be extraordinarily weak if they did exist. Their effects would be so slight that they would be useless for any practical purpose except possibly impressing the Nobel committee.
The fact that standard EM theory with zero magnetic charge works well only proves that normally there aren't lots of magnetic monopoles floating around: they could be very short-lived particles or strange phase of the matter, but still real and Maxwell's equations don't say anything about this.
As far as I know there's no mathematical or physical reason to outright forbid magnetic monopoles. On the contrary, there is a well-known argument by Dirac that says that if they would exist then charge is quantised, which we know it is. This is one of the reasons people are still looking for magnetic monopoles.
I don't really understand your point here. If we do discover magnetic monopoles (which would not necessarily be very weak but instead very rare) then we would take the equation
Div(B) = 0
And update it to say
Div(B) = sigma
Where sigma is a field describing the monopole density. Theres a ready "gap" in Gauss' law for magnetism where you can easily stick monopoles. Of course the divergence would be zero in the absence of monopoles, just as the divergence of the electric field is zero in the absence of electric monopoles, but decidedly non-zero when there's an electron around.
I think your point is the current Maxwell equations explain physics so well that if we change them to accommodate magnetic monopoles they would have to be worse. If I understand you right, it overlooks that we can add terms[0] to Maxwell's equations that don't affect predictions in a world free of magnetic monopoles:
∇⋅E = ρ(electric) / ϵ0
∇⋅B = μ0 * ρ(magnetic)
∇⨯E = -μ0 * J(magnetic) - ∂B/∂t
∇⨯B = μ0 * J(electric) + (μ0)(ϵ0)(∂E/∂t)
We could switch every physics textbook to using the above today, and the only difference would be setting ρ(magnetic) and J(magnetic) to zero when there are no monopoles in the problem.
[0] Griffiths Introduction to Electrodynamics 3E, Section 7.3.4
If anything it's frustrating that there aren't monopoles, because if there were, we could make the E and B equations symmetrical under interchange of the fields. It would be a lot prettier, and I think it would be easier to teach to undergrads.
I mean you could just do that and tell the students that the magnetic charge and current densities are always zero unless we eventually discover monopoles.
This is incorrect, you can put non-zero divergence of magnetic field and all the equations and predictions stays the same. Better it would make Maxwell's equations symmetric under exchange of fields and sources. \
> so close to zero that monopoles would be extraordinarily weak if they did exist
Why? I can't think of a reason why would this be the case? You are not solving Maxwell's equation for the universe. You can have divergence of electric field closed to zero because you have very low density (the field source) in the region you are studying.
I agree that one could say that, but it still only makes sense in a context where you have an object that has this kind of magnetism, i.e., a magnet. And the same is true of the "magnetism" whose discovery this article is describing: it's a kind of magnetic state of an object.
Paramagnetism/diamagnetism doesn't apply to "magnets", which I assume you use to refer to materials that have external magnetic field without applying external excitation.
> Paramagnetism/diamagnetism doesn't apply to "magnets"
I also said "objects" in the GP to this post. There is no paramagnetism or diamagnetism in vacuum. You need an object made of an appropriate material. I would not insist on calling such an object a "magnet" if there is an objection to that.
However, what is described in the article is a kind of permanent magnetism; the term "magnet" applies to that in any case.
Spintronics, which these magnets might be useful for, have several potential advantages for low power, speed and quantum coherence for quantum computing.
So a very nice discovery. Love how we keep finding strange new useful modes of matter at “the bottom”.
Computing substrates are far from reaching any kind of final form or limit.
The introduction of dramatically faster semiconductor memory chips pushed
bubble into the slow end of the scale, and equally dramatic improvements in
hard-drive capacity made it uncompetitive in price terms.[1] Bubble memory was
used for some time in the 1970s and 1980s in applications where its non-moving
nature was desirable for maintenance or shock-proofing reasons. The
introduction of flash storage and similar technologies rendered even this niche
uncompetitive, and bubble disappeared entirely by the late 1980s.
There was a Konami arcade cabinet that (tried to) use bubble memory! It was considered a failure. Also from Wikipedia[0]:
> It was considerably more expensive than ROM chip-based boards and extremely sensitive to electromagnetic fields that could render the game unplayable.
You can find the start-up sequence of these on YouTube. It’s pretty…idiosyncratic. It took forever because it had to physically warm the memory up. Though I guess taking forever is irrelevant if you are turning on a machine only once in the morning. In fact, the music in the ROM it plays while starting up was named “Morning Music”.
Amazing. I never realised it got to commercial production, just that
about 1985 it was heralded as the next amazing thing - with however many
libraries of congress per fingernail etc.
> with however many libraries of congress per fingernail etc.
That's a bold claim!
I found a NASA document from 1976 that expected bubble memory to reach about a terabit per cubic meter by the year 2000. And then you need over a hundred terabits for a library of congress. https://core.ac.uk/download/pdf/42884743.pdf
MRAM is available as a niche product, it just hasn't achieved the promise of being cheap and dense as dram, fast as sram, nonvolatile and higher write endurance than flash at the same time. It ticks maybe two or three of those boxes, which is still something.
We do. This is just a different way to build one. It's a configuration of atoms that we didn't realize could be made stable, and their atom-level magnets line up in a novel way. We understand atomic magnetism pretty well.
I highly recommend watching its video if anyone hasn't. It's got a nice groove, the lyrics are actually quite appreciative of nature... but the magnet line is a real weird inclusion.
EDIT2: The meaning of this statement is that the sum of magnetic lines of force entering a frame is equal to those exiting; there are no magnetic monopoles.
There are four fundamental forces that are observed: the strong nuclear force, the weak nuclear force, the electromagnetic force, and the gravitational force.
Why these forces exist, we cannot know.
How these forces act is a question of physics and mathematics.
:magic smoke: n.
A substance trapped inside IC packages that enables them to function
(also called blue smoke; this is similar to the archaic phlogiston
hypothesis about combustion). Its existence is demonstrated by what
happens when a chip burns up -- the magic smoke gets let out, so it
doesn't work any more. See {smoke test}, {let the smoke out}.
Usenetter Jay Maynard tells the following story: "Once, while hacking
on a dedicated Z80 system, I was testing code by blowing EPROMs and
plugging them in the system, then seeing what happened. One time, I
plugged one in backwards. I only discovered that after I realized
that Intel didn't put power-on lights under the quartz windows on the
tops of their EPROMs -- the die was glowing white-hot. Amazingly, the
EPROM worked fine after I erased it, filled it full of zeros, then
erased it again. For all I know, it's still in service. Of course,
this is because the magic smoke didn't get let out." Compare the
original phrasing of {Murphy's Law}.
curl -fsSL https://jargon-file.org/archive/jargon-4.4.7.dos.txt | LC_ALL=C sed -n '/^:magic smoke/, /^:/{/^:mail storm/d;p;}'
I believe GP is a riff on the common joke among physicists: "Anyone who claims to understand quantum mechanics is either lying or crazy."
To be more specific in the case of magenetism, you can say that, for example, ferromagnetism arises from the alignment of magnetic moments into cohesive domains, where the individual magenetic moments arise on the atomic level from unpaired electrons in the d or f orbitals.
But if you poke at that (incomplete) answer a little bit, things start to get complicated. How exactly do magnetic domains align? What if there's a disruption in crystal structure? Are there other sources of magnetic moments? Where does the magnetic moment on an elementary particle come from? The answers to these questions get pretty complicated and questions like these motivate a lot of active scientific research.
we don't know why or how there is electric charge (and their related fields), we just know that there is electric charge; it's one of the properties of the universe; same with gravity. We have uncovered mathematical laws of charge and and their relationship (via div, grad, curl and all that) to magnetic fields, but we don't know how or why, just what is.
"A map is not the territory it represents, but, if correct, it has a similar structure to the territory, which accounts for its usefulness." — Alfred Korzybski, Science and Sanity
You are confusing conceptual models of reality with reality itself.
The Scientific Method is used to construct an accurate, reliable, self-consistent, non-arbitrary representation of the world, which are models.
QED is one of the most stringently tested theories in physics. But it is a model and will never be proven as 'True', we just get more confident in he model after it passes test after test, after test, after test.
But it is still just the map and not the territory itself.
It's not illusory or an "artifact", since you can have electromagnetic field configurations that cannot be reduced to simple electrostatics (i.e., electric field but zero magnetic field) by picking an appropriate frame.
Special relativity helps to explain why, even if you have a configuration that is purely electrostatic in one frame, it won't be purely electrostatic in other frames. But that's not the same as saying that all electromagnetic field configurations are that way. They aren't.
