Talk:Demagnetizing field

Style of article

I like what you have done here RockMagnetist. The style of the article is in many ways different then what I am used to in wikipedia, though. I don't mean that in a bad way. I like a lot of the differences and I would rather conform for most part to the style you started. For one I am not used to the Harvard references at all. Physics journals have a tendency not to use it. I have a few questions so that we can work toward a more common style for this article.

• You want to reference by chapter which has the obvious advantage of being less version dependent. Some of the references though are hard enough to find even knowing the right section of the chapter. I don't know how important that is, especially when the reference isn't that common. (I was kind of surprised to see that you were able to find Nayfeh and Brussel, for instance. If Jackson or Griffiths covered it I would have used them instead since they are very common for physicists at least.) I will defer to you here, easily, since my understanding of WP citation policy both real and in practice is poor.
• Is there any way to delinkify the equation numbers or to make the links useful? I just copied and pasted the equation box template you used.
• Inline variables such as $\mathbf {H} _{d}$ appear too big to me. I have used wikistyle (H_d) in places but I personally think that doesn't look as good. (It seems to be the predominant style in physics WP articles, though.) The size will vary from browser to browser and style to style, etc.. Another option is to use \scriptstyle as in $\scriptstyle \mathbf {H} _{d}$. I don't know which is best but it is a small thing that would help the article style wise if we were consistent. The 'official' MOS:MATH prefers using the wikistyle but people are always breaking that style.

p.s. I am really excited that you took the time to write this article and I hope to reference this material in the magnetic field article sometime soon. TStein (talk) 16:57, 20 October 2010 (UTC)

I am delighted to have your input on the article, TStein. Some answers to your questions:

• It happens that the equation references didn't work for my edition of Jackson. I hear you about the difficulty of finding a particular equation - I wonder if there is a WP policy on that. One nice, if mostly aesthetic, consequence of citing chapters is that you can keep reusing the citation. As for Nayfeh and Brussel, I didn't find it - I just deduced that an equation numbered 6.xx was from chapter 6.

• I'm not impressed by Jackson's coverage of magnetism, by the way; he has some strange things to say about hysteresis. I prefer Chikazumi, Cullity and Aharoni (3 books). My impression is that Cullity is the easiest for most people to access, so if you like I could substitute citations from his book.

• The equation numbers can be referenced using the EquationNote template, as I do after equation 4.
• I don't like those oversized variables either. I have tended to use the math mode for three reasons: (1) I am more comfortable with Latex, (2) sometimes the Wikistyle variables look quite different from the variables in the numbered equations, and (3) I'm hoping that some day they will improve the Latex engine so the inline equations look good. With the third point in mind, I'll try \scriptstyle on the parts that I wrote.
• I like the article on the magnetic field, and it's nice to know that you will be referencing this material. I intend to create Shape anisotropy in the near future, extending the material on demagnetizing factor to include non-ellipsoidal shapes.RockMagnetist (talk) 17:35, 20 October 2010 (UTC)

I have experimented with \scriptstyle, and it's pretty good except for a single lowercase variable (e.g., $\scriptstyle z$ looks a lot worse than $z$). RockMagnetist (talk) 18:58, 20 October 2010 (UTC)

I have changed my mind. I just can't get inline Latex looking good. I have converted the document to the HTML form. Note that I am using x for non-bold variables. It looks more like the numbered equations. RockMagnetist (talk) 18:39, 26 October 2010 (UTC)

Questions about energy equations

Can you fill in the blanks about the energy equations. The first equation looks to me like it could be the energy needed to create a particular magnet, but typically the 1/2 in front means that it will only work for linear materials such that B = μH. The next two look like some sort of interaction energy where the magnetization of one is unaffected by the demagnetizing field of the other. (Hard magnets?) I confess, these energy equations can confuse me at time. Any help understanding these equations or extra references will be greatly appreciated. Thanks. TStein (talk) 03:14, 27 September 2011 (UTC)

Sorry I have been so slow to reply. I'm not sure whether to add a derivation because it's a bit technical and this page is already too technical. The starting point, however, for both the self-energy and interaction terms is the energy for a lattice of dipoles:

$E=-{\frac {1}{2}}\sum _{i}\mathbf {\mu } _{i}\cdot \mathbf {h} _{i},$

and the factor of 1/2 is there because each interaction is repeated twice. There is no restriction in terms of linearity or magnetization being unaffected by demagnetizing field. No textbook I have found derives the above equation, it's just considered a given. RockMagnetist (talk) 23:06, 31 October 2011 (UTC)

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