Can't be antiferromagnetism, so what is it?

[5614]

okay, this is the most confusing thing i've ever seen, i've taken it to my physics teacher and he suggested something to do with antiferromagnetism, but if it were that it still lacks in explanation for parts of it... so here goes.

 

if you really dont trust me then i can try and prove it to you, but the videos would be hard to do and even they could be fake so please trust me, what i say is weird but i swear on my life it's true, if im not specific enough, say so.

 

okay, so we start off, im obtaining a NIB (neodyium iron boron) magnet from inside an HDD, it took about 1 hour to do due to the screws blunt-ending and further problems, but in the end i got out the NIB!

 

here's what it looked like:

that's the NIB on a piece of metal it came out on, its glued there, i cannot get it off (i chipped a bit of it off trying! i promise its stuck and i done wanna try harder case i break it!)

now the magnet just featured is very powerful, keeping it the way up shown in the image (so the magnet is at the top and the metal piece which is bigger than it is underneath). so if you placed another piece of metal (which is attracted to magnets) ontop of the NIB, (so from the top of the image) it'd be attracted to the NIB. however, if you turn it upside down so the magnet is protected by the piece of metal underneath it there IS NO MAGNETIC FIELD PENETRATING THROUGH THAT METALIC SHEET. not a single bit.

 

so, said my teacher, this is probably caused by antiferromagnetism.

 

however...

 

then we have another piece of plain metal, the same metal (same composition, not actual same piece) that is glued to the NIB (both featured in 1st pic)...

 

then, this was kinda hard to photo, you put the 2nd piece of metal onto the NIB, so the NIB is in this sandwhich:

(metal (pic 2) on top, NIB middle, metal (bottom of pic 1) at bottom of this pic)

 

remember just a second ago there was no magnetic field on the bottom of the 1st pic... now there's a 2nd piece of metal, like in the 3rd pic there is a magnetic field underneathe it, there is also a magnetic field on top of it, there is a magnetic field everywhere on the 3rd pic.

 

summary:

you have pic 1

no magnetic field under it

add pic 2 (shown in pic 3)

now there is a magnetic field under it.

 

my physics teacher though possibly that the new 2nd piece of metal made it from antiferromagnetism to kinda anti-antiferromagnetism, however if you add a 3rd layer there is still a magnetic field, so anti-anti-antiferromagetism allows a a magnetic field through.

antiferromagnetism = no magnetic field through, possible pic 1

anti-antiferromagetism = magnetic field through, possible pic 3

anti-anti-antiferromagetism = magnetic field through, no photo.

but does this "anti-antiferromagnetism" exist? what is it? how does it work?

 

thanks for reading all of it, it was necessary, but should cover it all... do you know what causes this?

[The Rebel]

Are there any changes in the field direction???

 

I'm wondering if the metal is acting like a sleeper where field lines in the metal are going in the opposite direction to the internal "field" in the magnet. Therefore causing a closed magnetic current not visible to the outside of the sleeper.

 

By adding the metal on the other side it is doing the same. However because there is a outer loop magnetism would exist again, but perhaps in the oppsite direction.

 

 

Apologies, this is the best i could muster in paint.

 

EDIT: Actually looking at it again, the bottom plate arrow is in the wrong direction and the side arrows shouldn't be there.

[swansont]

What is the direction of the field - is it N-S as Rebel drew, or is one pole against the metal plate? And is it weaker when the two metal pieces are in place than the field when only one is there? (obviously the zero field area is weakest)

[Deified]

Well, I don't have to trust you at all, I have a similar set of magnets and metal pieces sitting in front of me. I retrieved them from my HDD as well. My preliminary tests show the same results as you.

[5614]

What is the direction of the field?

looking at this picture here:

same as above one, on the left is the north and the right is the south.

so the magnet looks like

nnnnnssssss

so its actually the other way around to how rebel drew it, but if you rotate the whole thing 180 then it comes back to what the rebel drew! im talking about it how it looks in the picture because its easier to understand exactly what im saying.

it is NOT north at the top south at the bottom... it IS how the rebel drew it (effectively).

 

By adding the metal on the other side it is doing the same. However because there is a outer loop magnetism would exist again, but perhaps in the oppsite direction.

i dont understand the reasoning for this, maybe an explanation of what outter loop magnetism is and why that causes the field to bypass the "sleeper" as you called it, how does sleeper work? like an antiferromagnet?

 

I have a similar set of magnets and metal pieces sitting in front of me. I retrieved them from my HDD as well.

newer HDDs seem to have a different looking, more metalic grey metal in that place, how old is your HDD?

 

about antiferromagnetism it is not that common, apparently, and also apparently (i've been reading about it) managanese compounds are the most common antiferromagnets and MnO is the most common, MnO is black, althought this is quite possibly covered in something or rather... I've contacted maxtor about the material it is, should get a reply in 2 working days, so monday or tuesday, i doubt i'll get an answer, but worth a try.

[RICHARDBATTY]

I have experienced something on these lines before. I think its an alloy property. The ferrous bits may form seperated magnetic fields within the alloy and cancel each other out. Its realy wierd to see though. With only one plate the fields have to form in the one plate but with two they can repel and become stable forming a polarized field in each plate seperatley. Could you mount the magnet and glue plate in a peice of wood long side showing through the face of the wood. Then have a slot to slide in the second metal plate. You could then do an iron dust pic on paper then add the second plate from underneath and watch the patern change if that makes sense.

[5614]

it makes sense but how would it help and i dont have any iron filings available for at least one week.

[swansont]

When add the bottom piece of metal, does it stick to the magnet? Is the magnet stuck to the top piece? If yes, is it by glue, or magnetic force?

[5614]

is it is by a small amount of glue.

 

the reason i know this is that there is nothing i can visibly see, however i know from personal experience the force required to move it if it was only magnetism and i used much more force and even chipped a small section of the magnet off and it didnt move a bit, there must be some sort of glue, but as i cant see any (it doesnt rise the magnet) there's a small amount.

 

whilst the glue may cause a shielding a metal generally does this and if it was glue the add 2nd piece metal and no shield affect thing is harder (so far i think) to explain...

[RICHARDBATTY]

it makes sense but how would it help and i dont have any iron filings available for at least one week.

Sorry its just a simple way of getting a picture of the field lines so you can see the change. You put paper over the magnet and put the filings on and tap the paper, the filings move to the field lines. Just thought you might like to observe the changes.

[Deified]

newer HDDs seem to have a different looking, more metalic grey metal in that place, how old is your HDD?

 

Its probably about ten years old, it looks almost exactly like the ones in your picture. I have been soaking it water for a few days, trying to loosen the glue, it doesnt seem to be budging.

[Rekkr]

Assuming the magnet has a north end and a south end, this would be caused by anti-antiferromagnetism. One plate on the north end, and two plates on the south end. It is impossible to have a double "anti" (negative perhaps?) on a two poled magnet.

[5614]

Assuming the magnet has a north end and a south end, this would be caused by anti-antiferromagnetism. One plate on the north end, and two plates on the south end. It is impossible to have a double "anti" (negative perhaps?) on a two poled magnet.

i can see why anti-antiferromagnetism would causes the initial magnetic field block as shown in picture 1, but i dont understand how anti-antiferromagnetism allows picture 3 to be true..... why does adding a 2nd piece of metal to the other side of the magnet stop all the shielding affects?

also the magnet is, if looking at picture 1, has the fields nnnnnsssss (where n is north and s it south!)

[swansont]

What is the direction of the field when the metal plates are in place - same as the magnet or opposite direction?

[5614]

What is the direction of the field when the metal plates are in place - same as the magnet or opposite direction?

 

It's the same direction... the north is in the same place and the south is in the same place.

 

incidentally, an addition to picture 3 is that this:

also works, in that it counteracts the magnetic field blocker and there is a magnetic field on all sides.

[5614]

in fact that 2nd piece of metal doesnt neeed to be touching the magnet at all, all it needs to do is be in the presence of the magnetic field of the magnet to cancel the magnetic field blocking affect of the bottom piece of metal.

 

VERY INTERESTING, POSSIBLE EXPLANATION:

 

picture:

the 2nd piece of metal, (as featured previously on top of the original NIB) now has been seperated and given its own NIB magnet (left).

NOTE: there IS a magnetic field underneathe the new metal/NIB pair (left in pic)

 

explanation: the glue attaching the NIB to the metal in the first NIB/metal pair (right above, previously the main thing in all pictures) is directly affecting if not causing this magnetic field blocking.

NB: i do not know if its glue, all i know is that there's something attaching the NIB to the metal which has caused a strong bond... i assume its glue.

 

NIB = neodiyum iron boron - its the magnet!

 

ok, so we know quite a bit, but any explanations would be great... can a glue have antiferromagnetic properties?

how does the introduction of a 2nd metal counteract this magnetic field blocking properties of (probably) the glue?

[swansont]

My guess was that the metal pieces are [math]\mu[/math]metal, which is metal that has a high magnetic permeability and is used for magnetic shielding. That would explain the lack of a field in the case of one piece - all of the field above the magnet goes through the metal.

 

But I can't see how adding a second piece would give you the field back, so I'm not convinced that this is the case.

[5614]

That would explain the lack of a field in the case of one piece - all of the field above the magnet goes through the metal.

just explain quickly... i dont understand how if the metal was shielding the magnetic field why the field goes through the metal, when surely the metal is shielding it???

[swansont]

just explain quickly... i dont understand how if the metal was shielding the magnetic field why the field goes through the metal, when surely the metal is shielding it???

 

Instead of getting the normal spread-out pattern of the field, it all goes into the metal. Thus the region above is shielded. A little like a magnetic "sponge" It would look very much like Rebel's first diagram, but the field would be stronger in the material, since you have concentrated it.

[5614]

OK, I understand your last post, but we still have the problem of adding the 2nd piece of metal...

But I can't see how adding a second piece would give you the field back, so I'm not convinced that this is the case.

we must remember post #16 which says how a single piece of that metal which looks identical and I am assuming is the same metal (same looks, from the same place etc) is attached to another NIB, the metal does NOT have a shielding affect, causing me to think that possibly the glue (again see post #16) is causing or affecting the magnetic field shield.

[swansont]

Glue is generally made of stuff that has no noticable magnetic properties.

[5614]

Glue is generally made of stuff that has no noticable magnetic properties.

you know, i've had the two cleverest physicists i've ever spoken to thinking about this... mainly because I only really know two! anyway, they've (Swansont and my physics teacher) both have had ideas, but none of them fully work.

 

I agree that glue would not normally have any magnetic properties, in fact, i've never seen a glue that affects a magnetic field... but if you consider that a different piece of that metal does not block a magnetic field and that the original piece of metal that looks identical does block it, what can it possibly be?

 

are the two pieces of metal which look identical actually different?

is there a glue or bonding agent affecting it?

[5614]

I got the response from maxtor (company who made the hard drive)

 

Hello Jonathan' date='

 

Here are some links which may answer your enquiries.

 

http://www.infomrt.com/readrite/magbasic.html

http://www.pcguide.com/ref/hdd/op/over.htm

http://www.pcguide.com/ref/hdd/op/act_Actuator.htm

 

Thank you for your patience and co-operation, if there are further questions please do not hesitate and contact us again.

 

Kind regards,

Steven Lai,

Technical Support Team, Maxtor Ireland LTD.[/quote']

 

here's a summary of the three sites:

 

Magnetic Phenomena used in hard drives

 

A. An electric current produces a magnetic field. (electromagnets)

B. Some materials are easily magnetized when placed in a weak magnetic field. When the field is turned off, the material rapidly demagnetizes. These are called "Soft Magnetic Materials."

C. In some magnetically soft materials the electrical resistance changes when the material is magnetized. The resistance goes back to its original value when the magnetizing field is turned off. This is called "Magneto-Resistance" or the MR Effect.

D. Certain other materials are magnetized with difficulty (i.e., they require a strong magnetic field), but once magnetized, they retain their magnetization when the field is turned off. These are called "Hard Magnetic Materials" or "Permanent Magnets."

 

the 'magnet assembly' is what I am referring to, I was able to seperate the top part form the bottom part. in the image it has been unscrewed and pulled to the left to make the electromagnet visible. the NIB magnet is stored inside the 'magnet assembly'. the electronmagnet can then be activated and attracts/repels which creates the movement of the read/write head (which is at the other end of the 'arm')

 

I will now contact maxtor again inquiring about the mysterious glue... I emailed them on last friday and got a reply tuesday... so i'll email them today (wednesday) and I should hear from them by monday latest.

[The Rebel]

Probably not important now, but I've only just got access to this thread again.

 

In my diagram I was thinking about how a sleeper you put on to the horseshoe magnet keeps it magnetised, which I believe is by maintaining magnetic flux.

 

My thoughts went along the lines that the "sleeper" prevented fields of flux coming out the metal into the open. By adding another on the other side, the magnetic current looked like a larger magnet but using the "sleepers" instead.

 

I'm going to have to probably print and read this now longer thread again, and see if anything bokos i've got can find answers.

 

Would be interesting to see what Maxtor say.

[5614]

My thoughts went along the lines that the "sleeper" prevented fields of flux coming out the metal into the open. By adding another on the other side' date=' the magnetic current looked like a larger magnet but using the "sleepers" instead.

[/quote']

ok, took me a while to fully understand that, but I think I do, my next question is SO?

 

I mean, what difference does it make if the field looks larger to the 'sleeper' ?

 

I mean, it might be totaly obvious, but I can't see what difference it makes. Although i accept your point that the metal will obtain an induced magnetic field.

 

==============

 

reading that.... going back, post #16 remember the picture with 2 NIB/metal pairs, the mysterious glued one and a new one which let a magnetic field through...

 

NEW ONE: place the NIB at one end of the metal, there's a magnetic field all the way along the piece of metal on both sides.

ORIGINAL ONE (with glued NIB): there's a magnetic field along the piece of metal on the side of the NIB - there is NO magnetic field on the other side (bottom side in the pic)