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Old 05-15-2018, 07:29 PM
bistander bistander is online now
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Bloch wall

I
Quote:
Originally Posted by dyetalon View Post
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From Wikipedia: "A Bloch wall is a narrow transition region at the boundary between magnetic domains, over which the magnetization changes from its value in one domain to that in the next, named after the physicist Felix Bloch. The magnetization rotates out of the plane of the domain wall, in contrast to Néel walls".
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Hi dyetalon,

Yes, thank you, I read that a few times plus much more on the subject. Notice that the first sentence says the Bloch wall is at the boundary between magnetic domains. Magnetic domains are a fraction of a mm in size, or even um. So an inch size magnet, or piece of ferro/ferrimagnetic material will contain millions of magnetic domains and similar order of magnitude number of domain boundaries of which many are likely to be Bloch walls.

Ufo, EM, and other members here believe there is a single Bloch wall in a magnet of handheld size and it separates the N domain from the S domain and is located in the middle and perpendicular to the magnetic axis. Here's my opinion on that:
Quote:
Originally Posted by bistander View Post
Quote:
Originally Posted by Ufopolitics View Post
That's right...that one...the one you called "bad science"...Rawls & Davis book.
Here is an example what these authors promote which I call bad science. Found in chapter three:



Then they end chapter with what I find disgusting:

Quote:
We are closing chapter three with the discussion and drawings presented only to better explain magnetism, the rate of flow direction, the two poles, the division of the two poles, and the potential force as to the electronic charge potential of each pole. This allows a reference to scientists who may not have continued into the physics of electrodynamics. Students and instructors should attempt to upgrade and correct any older text materials that differ from today's concepts and understandings of the basic of magnetism as presented herein.
All because they observed a bubble drifting on a microscope slide between magnets in 1936. From what I call tell, this bad science was the beginning of the misuse of "Bloch wall" and spinning static magnetic fields. The origin of fantasy magnetism.

As long as I have started and have the Rawls & Davis diagram shown (attch#1), I'll explain some of what's wrong with it. When you do a Google image search for Bloch magnetic domain wall, you see hundreds of hits most looking like attachment #2.



From: Domain Wall Magnetoresistance

Now compare the two diagrams. The primary discrepancy is the labeling of the N & S surfaces. The arrows represent particle or crystal dipoles and point to the N end of the dipole. So the surface of the domain to which the arrows (dipoles) point will be the N side (pole) of the domain which is the top left as shown in attch#2. Similarly, the bottom right will be that domain's N making the upper right surface S as indicated in attch#2.

Notice in attch#1 that Rawls & Davis apparently misread such a diagram and labeled the end surfaces N and S. This makes a huge difference. They continue bad science assuming they're looking at a diagram of a magnet of handheld size when the domains, of which there are two shown, are but a small fraction of a millimeter in size. And then their third piece of bad science is to assign spin to the magnetism. I won't even touch their ridiculous broken figure 8. The whole deal stinks.

Regards,

bi

Quote:
Originally Posted by dyetalon View Post
The Bloch region is where North turns into South another way of looking at it: where the 'field' reverses polarity.
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The "Bloch region" actually has a different meaning used in quantum mechanics at the subatomic level. It was in this field where Felix Bloch was awarded the Nobel Prize. I can only wonder if he rolls in his grave.

Regards,

bi
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Last edited by bistander; 05-15-2018 at 09:59 PM.
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