Talk:Ferromagnetism

How do rare earth magnets work?

Isn't Neodymium ferromagnetic? It is used in neodymium magnets, some of the most powerful permanent magnets ever made, and according to the page on Neodymium, it is a ferromagnetic. 72.45.61.218 19:09, 6 April 2007 (UTC)

Yes, I was wondering if someone could add a simplified explanation of how rare earth magnets differ from previous permanent magnets. What makes them so much stronger? I assume they work by the same 'exchange energy' mechanism as other ferromagnets. And who invented them? This doesn't seem to be addressed in Rare earth magnet or Neodymium magnet or elsewhere. --Chetvorno 21:59, 11 August 2007 (UTC)

I think it may be because rare earths can have more unpaired electrons than transition metals, as there are more orbitals that can be partially filled (7 f orbitals vs 5 d orbitals). --Itub 13:39, 10 October 2007 (UTC)

For the rare earth magnets two things come together: a high moment for the ions and large magnetic anisotropy. This translates to high saturation and high coercivity.--Ulrich67 (talk) 22:49, 2 January 2012 (UTC)

There is a little material on rare earth magnets in Magnetism. RockMagnetist (talk) 19:14, 3 January 2012 (UTC)

Okay, short version that I teach in general chemistry 1 is that the 6s² orbital lies so closely to the 4f orbitals that it the energy needed to promote the s-orbital electrons into that f-orbital is very low. In fact, even though the usual Aufbau Principle and Hund's rule would lead us to [Xe].6s².4f⁴ as the electron configuration there is one more factor at play and that is same spin stabilization.

In general, when an orbital is either halfway (3d⁵ or 4f⁷)) or all the way full (3d¹⁰ or 4f¹⁴) of electrons there is a stabilizing effect. This is part why it is often easier to have a 2⁺ cationic from loss of the electrons from the s-orbital than from the d-orbital or f-orbital, the larger set of stabilized spins are harder to remove electrons from. It is pretty common for d-block elements to have all of their electrons in the d-orbitals and none in the s-orbital because the energies involved favor it. The same holds true, only more so, for the f-block elements like Nd.

Put the closeness of the s-orbital energy level with the f-orbital energy level together with the idea of the spin stabilization of having six electrons with the same spin direction and it is almost trivially easy for all of the electrons to be very stably in the f-orbital instead of the s-orbital. In reality, that means Nd finds the [Xe].4f⁶ electronic configuration to be energetically favorable. Six unpaired electrons with the same spin is more than the 5 (or extremely rarely 6) of magnets from the d-block elements. This explains why rare earth magnets are so strong. They are highly stable in a magnetic configuration that has lots of electrons unpaired.

I actually assign a thought experiment to my chemistry lab students to suggest what elements in the f-block would they think would be the best magnets and to explain why they think so.

There is more depth to this and this is an active area of research in inorganic chemistry, materials science, and metallurgical sciences. The Organometallic Chemistry of the Transition Metals by Crabtree and Inorganic Chemistry by Miessler and Tarr are both good upper level undergraduate advanced inorganic chemistry books for further detailed reading. If you have not quite made it to that level yet, you can find more elementary explanations in just about any general chemistry textbook for college level chemistry students.

https://www.google.com/books/edition/The_Organometallic_Chemistry_of_the_Tran/bqagDwAAQBAJ?hl=en&gbpv=0

https://www.google.com/books/edition/Inorganic_Chemistry/oLQPAQAAMAAJ?hl=en&gbpv=0&bsq=inauthor:%22Gary%20L.%20Miessler%22

https://openstax.org/books/chemistry-atoms-first-2e/pages/3-4-electronic-structure-of-atoms-electron-configurations

Best, Dr. Moulder South Dakota School of Mines 64.179.156.89 (talk) 05:54, 5 February 2024 (UTC)

Interacting magnetic fields

There is a lot of discussion of the properties of various types of magnetic materials as to how to maximize the internal properties or the materials. However there is practically no discussion of what controls the intensity of magnetic force activity in the interacting field spacial volume. If a suspended magnet is swung like a pendulum over an opposing polarity magnetic the interaction of the fields will control the physical activity (motion) of the moving magnet at some distance. The question is as to how this magnetic force is capable of being extended so as to continue to act is not discussed.WFPM (talk) 23:54, 16 February 2012 (UTC)

Diagram request

I think this article could benefit from a hysteresis diagram like found in standard textbooks and like can be found in the ferroelectricity article:

http://en.wikipedia.org/wiki/Ferroelectricity

129.63.129.196 (talk) 15:59, 19 November 2012 (UTC)

And then you can write something like my removed sentence, but maybe more clarified: "The most important parameters of the ferromagnetic material constitute its magnetic hysteresis loop." Because on that diagram one can see magnetic parameters of a given ferromagnetic material, determining its possible utilization: coercivity and so on. Niuthon (talk) 07:33, 24 July 2014 (UTC)

A section on hysteresis would be good, with a diagram and a discussion of some of the hysteresis parameters. Even if such a section is created, though, there remain a couple of problems with your statement . First, the "most important" label is arguable: one can also talk about more fundamental parameters like the magnetocrystalline anisotropy constant. Also, you're really talking about a particular hysteresis loop, the main loop. Clearly that must be clarified in the body of the text before adding a statement to the lead. Note also that, per MOS:LEAD, the lead should summarize the content, not add significant new information. RockMagnetist (talk) 14:55, 24 July 2014 (UTC)

Domain images

We now have a superabundance of domain images, spilling down past the next two sections and into References. Do we really need all of them? I like the first and fourth images, but the second and third are hard to interpret. RockMagnetist (talk) 17:23, 19 December 2012 (UTC)

I agree, the second and third should be removed. -Chetvorno^TALK

There being no objection in two years, I have removed the images. RockMagnetist (talk) 14:58, 24 July 2014 (UTC)

Exchange interaction

First line in the section is utterly wrong. Nearby dipole magnets prefer to align their poles. The paragraph even cites the dipole-dipole interaction page which includes the Hamiltonian for the interaction. Taking a look at that Hamiltonian clearly indicates that two dipoles prefer to have their moments aligned along the separation vector. That gives the lowest energy configuration. — Preceding unsigned comment added by 2601:D:CA00:207:608B:6A12:87DB:AF1E (talk) 06:40, 6 March 2015 (UTC)

This confusion arises because the configuration is incompletely stated. Presumably what is meant is that "two dipoles that are free to rotate in any direction will tend to align with their dipole moments perpendicular to the vector separating them, and oppositely oriented with respect to each other". If the orientation of one dipole is constrained to being parallel with the separation vector, then second dipole will align itself with its dipole in the same direction as the constrained dipole. The sources are unclear on this, so it is worth extending the wording along the lines suggested by me here. Otherwise, we will continue to get this kind of reaction. —Quondum 15:09, 6 March 2015 (UTC)

Actually, both the parallel and perpendicular orientations are stable without the need of constraints, so it depends on initial conditions. However, over larger scales a collection of interacting dipoles will arrange themselves so their moments nearly cancel out (see Demagnetizing field). Still, books on ferromagnetism don't preface discussions of the exchange interaction with this information, so maybe we don't need to either. Maybe it would be better to contrast the effects of the exchange interaction with diamagnetism. RockMagnetist(talk) 17:06, 6 March 2015 (UTC)

to Quodom, that isnt correct. The lowest energy configuration is parallel orientation and pointing along the separation vector. This gives -2 (d1 x d2)/r^3 as the energy. The second lowest is the perpendicular to separation vector and opposite orientation. This gives -1 (d1 d2 )/r^3. D1 and d2 are the dipole moments. — Preceding unsigned comment added by 165.124.129.66 (talk) 18:22, 6 March 2015 (UTC)

@IP.66: I was making an assumption based on the bare assertion in the references, but I have no objection to what you say. However, based on what RockMagnetist says, each of the two configurations mentioned are at a local minimum in the total energy, so the situation is more complicated than I stated.

@RockMagnetist: IMO, WP should not take its lead on style from texts that leave the reader scratching their head, and saying, "Hmm, this can't be right." Often enough, even such texts do make contextual assumtions that can usually be deduced by a careful reading of the preceding text (sometimes, this means reading the entire set of preceding chapters with expert foreknowledge). For example, many texts do not explicitly state whether they are dealing with natural numbers, integers, reals or complex numbers, but the expert will be able to determine from the applicability of the conclusions what the implicit assumptions are. Your own statement here about stability of both configurations suggests that the references are, to put it bluntly, incorrect in the general case. The bald statement, as quoted, seems to apply to an isolated pair of dipoles, but neither the parallel nor the antiparallel configurations extend naturally to arrays of dipoles such as occur in crystals. So, as stated, I support the "dubious" tag: the statement definitely needs work. (The diamagnetism suggestion might be a nice and noncontroversial contrast, but completely fails to address the question this text tries to deal with.) —Quondum 19:53, 6 March 2015 (UTC)

@Quondum: Depends which references you mean. If we follow the lead of texts like Chikazumi or Aharoni, I don't think there will be a problem. But I agree with the dubious tag. RockMagnetist(talk) 02:43, 7 March 2015 (UTC)

I was refering to the two sources given at the end of the sentence. These say, respectively:

• Joy Manners, Static Fields and Potentials: "It is important to notice that the interaction which gives rise to the magnetic ordering is the electric repulsion of electrons. [...] – as may be familiar to you if you have played with a pair of magnets – magnetic interactions cause dipoles to align in opposite directions: colloquially, north pole to south pole."
• Hans J. Kreuzer, Isaac Tamblyn, Thermodynamics: "According to classical electromagnetism, two nearby magnetic dipoles will tend to align in opposite directions."

I see nothing in the immediate vicinity in either of these to clarify what we have been speaking of, and it seems to me that these particular sources should not be used for this statement at all. Their focus is, after all, not classical physics. The first sentence that I quoted above illustrates the lack of rigour: the exchange interaction cannot be described as "electric repulsion", because it has nothing to do with electromagnetism (although the source of the energy does largely arise from electric repulsion/attraction of the different orbital configurations, but it would be improper to call this the exchange interaction). Chikazumi, Physics of Ferromagnetism makes for interesting reading, and seems pretty thorough. Pages 6–7 give a classical treatment of the potential energy of a pair of dipoles, and a statement that parallel alignment along the the axis of separation is stable and that parallel alignment transverse to the axis of separation is unstable; antiparallelism is not dealt with in as much detail, but it seems that the situation is reversed.

In all, I think that we should simply remove the statement about alignment related to classical magnetism. Chikazumi says (p. 130) that "The value [of the difference of the Coulomb energy between parallel and antiparallel unpaired electron spins] estimated from (6.42) is [say 1% of] 10⁵ times larger than the magnetic dipolar interaction calculated from (1.17)." I think that this would be a far more sensible point to make in the article – essentially that the interaction between magnetic moments is completely swamped. —Quondum 06:01, 7 March 2015 (UTC)

I agree. RockMagnetist(talk) 16:04, 7 March 2015 (UTC)

Okay, change made. —Quondum 20:59, 7 March 2015 (UTC)

Room temeprature ferromagnetism in transition metal oxides

I was wondering if it's worth making a new section about this topic. It appears that it has only been researched recently and it is not yet well understood as it occurs only under particular conditions. Here is a link to an article that got me thinking about this: http://www.sciencedirect.com/science/article/pii/S0921510715001622

Charbon (talk) 17:36, 27 June 2015 (UTC)

My feeling is that it doesn't merit a separate section but just a sentence or two. This article already has several sections, Actinide ferromagnets and Lithium gas that give WP:UNDUE WEIGHT to exotic ferromagnetic species. All these should probably be boiled down to a few sentences. --Chetvorno^TALK 19:49, 27 June 2015 (UTC)

Why do some materials respond to magnetism and others do not?

If this is covered somewhere, I missed it. I think the article should cover this. It explains magnetism in terms of electrons, but never discusses why electrons have magnetism. It's not in the electron article either. deisenbe (talk) 13:50, 25 December 2015 (UTC)

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I pointed out an error.

A triple one, that is: Neither C, nor Al, nor P are metalloids. 80.98.179.160 (talk) 08:17, 20 March 2018 (UTC)

Depends who you're asking. There is no rigorous definition of what a metalloid is and many elements have been included as such, including C, Al, and P. Double sharp (talk) 13:59, 20 March 2018 (UTC)

Explanation of the mechanism of ferromagnetism

The Wikipedia pages for Ferrimagnetism, Antiferromagnetism, Paramagnetism and Diamagnetism all begin with a succinct explanation of the mechanism involved, each involving a diagram that shows the magnetic moments of the atoms or molecules involved. I understand that ferromagnetism is a more widely used term than any of the above, but for people looking to understand the differences between the types of magnetism, I think a section formatted in parallel to the explanations on the above pages could be useful. Dinithi2 (talk) 03:10, 27 April 2018 (UTC)

That's a good idea. RockMagnetist(talk) 16:08, 2 May 2018 (UTC)