Roy Davis and Rawls Magnetism Discoveries

[tim123]

Hi Hanon,
  I think this is an interesting subject. Good call. Good links.

Hi, MileHigh,
  you can see the Bloch Wall with the green-magnet-viewing-plastic. I've tried it, and it's very clear.

I'm not sure I understand your objection to the concept. It does seem to be accepted. Perhaps you could elaborate on why you object?
http://en.wikipedia.org/wiki/Domain_wall_(magnetism)

I'd noticed the lack of field at the center of a coil in practical experiments too - it's a consideration for my Fin-motor design, (that I * will * build soon)...

When you cut a magnet in half - it becomes two magnets - so yes, the BW does 'move' in a way. I think it's a property of the bulk material, rather than individual molecules... Magnets, like many things in this holographic universe, have some of the properties of holograms.

Regards
Tim

[tinman]

You could look at it like this.Lets say the north field is hot water,and the south field is cold water. The two mix together,and you have warm water. The point is,although you now have a mix of the two-they are both still there-there not just gone.
I hate that word-the bloch wall-sounds so berdini.
Two of the video's you posted Hanon ,contradict one another. Do you know which two im refering to?

[MileHigh]

Tim123:

What is the green magnetic field plastic really telling you?  Have you ever thought about that?  What does it mean when it's dark, and what does it mean when it's light?  What is going on?  What does it really and truly mean?  I have seen so many clips where people play with that film and nobody seems to be concerned with this.

So you point to a white line on the green film and say, "That's proof of a Bloch wall."  Really?  Make a clip first that explains what the green film is actually doing and how you interpret the patterns of dark and light on the film when it interacts with a magnet.  Then apply that knowledge to what the green film is telling you when you think that you are looking at a "Bloch wall."

Your Wikipedia link is perfectly legitimate and it has zero relation to the imaginary Bloch walls that some people believe are inside permanent magnets.

http://www.youtube.com/watch?v=UVrwNIWlbcE

What people should try to get from the above clip is that if you have an imaginary sphere, the net magnetic flux through the sphere is always zero.  Whatever flux comes in also has to go out.  So if the imaginary sphere was inside a bar magnet with one half in the alleged Bloch wall area and the other half where there exists a magnetic field, then there would be a net magnetic flux through the imaginary sphere.  But this is impossible, the net magnetic flux through an imaginary sphere is always zero.  That means the magnetic field is consistent through the bar magnet as per the diagrams I posted.  Here's where you need an open mind and some imagination to get this.

MileHigh

[tinman]

Take note from 2:17.
http://www.youtube.com/watch?v=C9zaPH_DaxM

[tim123]

Hi MH
  I understand that the alternative explanation would be that the line shows the point where the N & S fields * cancel each other out *, as opposed to a point of genuinely no flux. Admittedly, it's hard to test, but given Howard Johnson's extensive experiments with mapping fields using stepper motors and a 3D Hall-effect sensor, I'm inclined to at least take his opinion seriously.

Surely if the Bloch wall exists in magnets at all, it has to exist in permanent magnets? I didn't think there was any qualitative difference between PMs and EMs...

I understand the difference between a monopole & a dipole that the vid explains.
1) My understanding is that the BW is a 2 dimensional plane - so you couldn't have the imaginary sphere you describe where half is 'in' the BW:

The magnetization rotates through the plane of the domain wall

2) As magnetic lines of force are circular - it would make no difference anyway... At least I can't imagine what you're describing... (perhaps a diagram?)

I'm going to have to test the field inside a coil properly - as part of the Fin-Motor work. Is there any experiment you can think of which would actually resolve the question to your satisfaction? If so - perhaps I'll do it.

The question:

What is the true topology of the North & South magnetic fields?

a) Is there one field circulating N to S through the magnet - as traditionally described?
b) Are there 2 opposite fields emanating from the 2 halves of the magnet, separated by the Bloch Wall?
c) Are there 2 opposing fields N and S, both going in opposite directions to each other through the length of the magnet.
d) other suggestions?

Certainly interesting stuff...


Tim