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Author Topic: the Bloch wall  (Read 17141 times)

pinestone

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the Bloch wall
« on: July 16, 2008, 06:14:33 PM »
Hi all

I've moved this discussion from another thread. We were talking about the Bloch wall, and the null zone of magnetism.
This is where north twists into south and is an elusive topic, to say the least.
There's not much information out there on this subject, but I'd like to discuss it anyway.

A while back, I placed two little neos on the surface of one of my lenses and produced this image.

Additionally, I used a modified computer monitor that has a Sony Trinitron CRT. Placing a 1 Tesla magnet (yellow shrink tubing around it) on the screen produced the other (larger) image.

I think both are representing the lowest potential of the magnetic flux, and both reveal the Bloch wall.

Comments?

Onevoice

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Re: the Bloch wall
« Reply #1 on: July 16, 2008, 07:13:24 PM »
Sorry, I don't have constructive comments. Not sure I understand the 1st picture. Can you please explain more about what and how it represents and on the 2nd picture. Can you please point out the north & south poles. Are they top-down or left-right?

pinestone

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Re: the Bloch wall
« Reply #2 on: July 16, 2008, 09:35:38 PM »
Sorry, I don't have constructive comments. Not sure I understand the 1st picture. Can you please explain more about what and how it represents and on the 2nd picture. Can you please point out the north & south poles. Are they top-down or left-right?

You can read about the lens here: http://www.nanomagnetics.us/

The magnetic orientation is N and S on the ends of the magnets in both images.
These are the separate images that I combined in Photoshop to create this:

Onevoice

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Re: the Bloch wall
« Reply #3 on: July 20, 2008, 08:21:11 AM »
Is there any kind of scale for the colors. Are they just alternating bands or does the color imply a certain flux density?

Its interesting that the envalopes of the fields look like they're almost perfect 45deg angles. What shape is the magnet you're using?

pinestone

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Re: the Bloch wall
« Reply #4 on: July 20, 2008, 04:01:46 PM »
Is there any kind of scale for the colors. Are they just alternating bands or does the color imply a certain flux density?

Each color on the crt image represent a different phase of the magnetic field. Blue is neutral, violet is north and yellow is south.
I'm not sure why there are multiple bands of colors (instead of one set), but it must have something to do with the induced field into the microgrid of the crt. I haven't thought too deeply about it. Maybe someone else reading these posts can offer an explaination.

The reason these colors are not the typical ones (red, blue and green) is that the crt I used for these tests has one defective gun.
I modified an old computer monitor by applying a small dc voltage to the video inputs (which turn on the video circuits), but sometime during my testing, i managed to destroy 'green'. The fact that we still get three different colors is what convinced me we are seeing the phase shift of the magnetic field. I have more pix using a different monitor in which all three guns work properly- I'll post a couple of them when I get back to the lab on Monday.

Quote from: Onevoice
Its interesting that the envalopes of the fields look like they're almost perfect 45deg angles. What shape is the magnet you're using?

These two images were taken using cylinder magnets. But regardless of the type of magnet used, the resulting images are the same.
What's not apparent in this image, is the crt image is two dimensional whereas the Flux Resonator image is three dimensional in real life. One of my collaborators is setting up a new experiment utilizing two cameras so the resulting images appear as 3-D. I'll post a link to his work when he makes them available.
« Last Edit: July 20, 2008, 05:05:14 PM by pinestone »

pinestone

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Re: the Bloch wall
« Reply #5 on: July 20, 2008, 07:31:12 PM »
In addition, I think it's relevant to add these images to this discussion.
The first image is one of a piece of paper with a 'star' pattern made from black tape.
A video camera is focused on this paper and its output is fed into a Sony crt.
The second and third images are of a cylinder magnet placed on the face of the crt, and each results in 'twisting' the image while displaying the magnets field at the same time.
The forth image is one that I 'borrowed' from the Wolfram math site showing the derivitive of a 2D Gaussian field. Notice how the graphic matches the crt image perfectly.

Note that the magnet is oriented 90 degrees different than the images in my previous post. Instead of the field being parallel to the glass, it's perpendicular.
These images were made by my good friend and fellow collaborator, John Shearer: http://www.nanomagnetics.us/jshearer.htm

pinestone

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Re: the Bloch wall
« Reply #6 on: July 21, 2008, 05:05:02 PM »
Here are a couple of images of a sphere and cylinder magnets on a 'good' Sony Trinitron:


Onevoice

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Re: the Bloch wall
« Reply #7 on: July 23, 2008, 06:10:26 PM »
I started to post this before, but the website hiccuped and I lost the text. Needless to say, wife and kids prevented me from getting back until now. Ok, those pics are way kewl and I see something weird. The first pic, quad I think, shows a definite 4 node pattern. I agree, I think you have a good captured image of the Bloch wall. I also think you've captured something else. Images of null zones right in the middle of the poles as well. It looks to my untrained eye that the fields are toroids with the wall between them and also null areas in the center of each torus. The southdown and northdown pics also seem to confirm this and show a rotation perpendicular to the field alignments but instead of the torus, the field lines look more like envelopes. Yet again, the sphere and cylinders are different again, showing what I would have expected, a singular envelope of field lines with no poler or Bloch wall null zones. I wonder, are all of your samples using Neos or are some of these other types of magnets and what are the alignments of the sphere and cylinders pics?

ps. Have you tried a hard drive magnet. They are double aligned through the face.

barbosi

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Re: the Bloch wall
« Reply #8 on: July 23, 2008, 07:03:51 PM »
pinestone, thanks for the pictures.

I like the second picture (quad.jpg) it shows the bloch wall area not being dead.

I particularly like the 5-th and the 6-th pictures (southdown.jpg and northdown.jpg)
I have no words, the pictures themselves are sugestive.
I will just use out of context your saying,

This is where north twists into south ...


 Regards.

pinestone

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Re: the Bloch wall
« Reply #9 on: July 26, 2008, 02:15:34 AM »
Yes, the crt displays are mind boggling. It's like having a particle accelerator.
http://science.howstuffworks.com/atom-smasher2.htm

Even though I understand the technology behind the cathode ray tube, these magnetic patterns are still fascinating and open to interpretation. For example, why are there multiple sets of bands? Are they representing actual concentrations of flux?
If you know anything about the composition of a color crt you realize the three colors- ie red, blue and green are at equal phase from each other. The above images seem to suggest that each concentrated band of flux is 'moving' in a different reference frame (time).
Looking at my images (above), red is north, blue is south and green represents 'neutral' or the region where these two opposites meet (Bloch wall).
I believe these images represent a 'slice' of the field. Like cutting an onion in half. There's no doubt in my mind that the field is composed of opposites. If we discard common belief and imagine the bands of flux are 'traveling' in opposite direction, this would still satisfy any magnetostatic equation and equal zero at rest.

pinestone

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Re: the Bloch wall
« Reply #10 on: July 26, 2008, 05:47:39 AM »
In addition, I'd like to note that the demodulated color signal from the video is NOT a factor in the above images.
The guns  http://electronics.howstuffworks.com/question694.htm  are turned on, but they are not receiving modulation from the video circuits. The images you see are a result of the magnets' field being induced into the micro-grid: http://en.wikipedia.org/wiki/Aperture_grille  plus the interaction of accelerated electrons passing through and then colliding with the phosphors on the screen.

The patterns are a 'mapped' representation of how the field is distributed throughout the metallic micro-grid inside the crt.

Bear in mind, a shadow mask style crt will not display the same patterns: http://en.wikipedia.org/wiki/Shadow_mask




sadang

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Re: the Bloch wall
« Reply #11 on: March 18, 2015, 10:41:47 PM »
@pinestone

Bellow I tried to make my own analysis and interpretation of some images from your movie https://www.youtube.com/watch?v=klw8y6ksxj0. I assume that in this experiment was used only the blue electron gun, otherwise the transition from one color to another should be in gradient. In these images the transition from one color to another is done directly.

a - observations
--- the shapes are almost the same as learned from school books.
--- the left and right shapes are mirror images of each other.
--- the up and down shapes are mirror images of each other.
--- there are two lines of symmetry in 2D (two planes in 3D), defined by the two vertical an horizontal axes of the magnet.
--- when the magnet is returned upside down, the planes of symmetry are also changed.

b - technical analysis
--- three beams of electrons (or only one) hit always the three (or only one) RGB phosphor vertical strips, from left side to the right side of the screen to create a single line.
--- for a dot pitch of about 0.25mm will result a specific number of RGB vertical stripes according to the physical size of the screen
--- for a 16 inch viewable area will result a number of about 1600 RGB stripes x 1200 lines for a single frame
--- will be required about 16 milliseconds for a single frame, 13.88 microseconds to scan a single RGB line and 8.6 nanoseconds to light a single RGB pixel and change to the next one.
--- 60 frames per second, 16x10^-3s for a single frame, 1.388x10^-5s for a single RGB line, 8.680x10^-9s to light a single RGB pixel.
--- the three beams (or only one) of electrons are deflected in the right or left side of the vertical axis of the magnet, according to which pole is up and down.
--- the three electrons beams (or only one) will be deflected with a greater angle at the vertical axis of the magnet than at a specific distance from it, proportional with the distance followed by the electrons beams (or only one) through the magnetic field until they touch the screen.
--- at the vertical axis of the magnet the distance followed by the three electrons beams (or only one) through the magnetic field of the permanent magnet will be maximum, and at the margin of the CRT's screen the distance will be minimum.

c - shapes analysis
--- the repetition of RGB colors sequence tell me how is the shape of the magnetic field in the plane of that specific electrons beam (horizontal line of scanning).
--- the width of each colored curved strip tell me about the width of the arc segment of the magnetic field. Short width toward the vertical symmetry axis of the magnet and longer width toward the faraway distance from the vertical symmetry axis.
--- the curvature in the vertical plane of the colored strips tell me the magnetic field have a decreasing curvature in vertical plane and all around the magnet toward its magnetic poles.

While for images with the magnet in vertical position, that is, with the magnetic lines of force perpendicular to the scanning direction of the electrons beam, I can understand somehow the resulting colored shapes on the CRT's glass, for the images with the magnet in horizontal position, that is, with the magnetic lines of force parallel to to the scanning direction of the electrons beam, I can't find any explanation for the resulting colored shapes. As you said, what we see here is the result of interactions between the beams of electrons from the three electron guns and the magnetic field of the magnet, which pass inside beyond the glass of the CRT. Of course all that in the case when all three electron guns are working, but according to my experience with delta CRTs, even with a single electron gun the shapes obtained and colors will be the same. Now, you know better if in this movie you had all three electrons guns working or only one.

Now, according to my understanding, the shape obtained with the magnet in vertical position, should be also obtained when it is in horizontal position. 

I'll be back soon with my own images and more analysis, because I came into possession of a Sony Trinitron 21" monitor.