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.
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.
I would prefer this headline.
https://en.m.wikipedia.org/wiki/Magnetism#Types
And I am not sure it can be called a magnet. It's definitely a new kind of magnetic state
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.
Sometimes words are slightly ambiguous. This is not a hill to die on.
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.
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.
Not too many got the joke it seems :D
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.
∇⋅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
http://www.av8n.com/physics/maxwell-ga.htm
(or even just equations (3), which make symmetries more apparent)
> 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.
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 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.