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Magnets and Magnetic Materials

12/12/2008 2:45 PM

I have done much research online about magnets and their properties but I still need help with what I have learned...

I have read that materials that can be used to make magnets are already magnetic but there are what is called domains with in the materials that are randomly aligned and the placement of the materials in a powerful magnetic field will align these Domains producing a usable magnet until external forces acting on the material misalign the domains once again....

These domains are pictured as very small shards or sliver shaped partials with in the material.....

Now what I need to know would it be possible to break down the magnetic materials into the individual separate domains and physically bond them back together in proper alignment in order to make a sheet magnet that would have the domains bonded permanently in correct alignment.

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#1

Re: Magnets and Magnetic Materials

12/12/2008 3:37 PM

That's easy to do with heat or a very powerful field. Or you could just grind up the material, put it in a suitable binder and then magnetize it. Since you're on GlobalSpec, search for magnet sheet.

Do you have some special kind of magnet in mind?

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#2

Re: Magnets and Magnetic Materials

12/12/2008 8:46 PM

permanently would have to be a NdFeB. using electron spin from a radioactive isotope (Nd) otherwise ceramic or just normal metalic magnets will lose strength when hit, heated, or exposed to a strong magnetic force. Im not sure if you can allign ALL of the domains, but if you heat the material past its curie temp, then induce an electro magnetic field until it cools down, it makes it magnetic, or sinter under compression. if you are worried about it losing strength, a plate for example, you could always run a current through it, or around its perimeter, electro-magnet, to ensure ALL or most of the domains remain alligned continuously. or you could super cool it with liquid nitrogen, super conducting magnetic plate, probably overkill. easier yet... if you only need one side of the plate, if it is iron or another ferromagnetic material, place a large ceramic magnet on the unused side, it will permanently be saturated with magnetic field.

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#5
In reply to #2

Re: Magnets and Magnetic Materials

12/13/2008 7:40 AM

Hi,

"not sure if you can align ALL of the domains"

I heard that not 1% are aligned.

"then induce an electro magnetic field until it cools down, it makes it magnetic"

this procedure is used to produce magnetically anisotropic material, which is better in the direction that magnetic field had at cooling. But later magnetisation is still needed.

Magnetic field strength cannot be maintained at the level that is needed for magnetisation.

The SmCo and FeNdB require magnetic flux density above 3 Tesla, as this flux density cannot flow inside soft magnetic material the coils for magnetisation have to be without any iron: air-coils, consisting of copper, insulation and some glass-fiber-epoxi to have strength against magnetic force.

As 1T translates to 1260 (amperes x turns) per millimeter of coil length this current can be maintained only for a very short time.

So a big bunch of capacitors (high-voltage) are charged slowly and connected by a 100KA switch to the magnetising coil. That has often many mm² cross-section and has to be designed to allow for the current (derived from capacitor voltage) limited by resistance and inductance (including the capacitors). And the inductance has to be designed to give a long enough impulse. The magnetic material is electrically conductive, so there are eddy currents at switching on the coil. These prevent the magnetisation to reach the center of the magnet: poor magnetisation if pulse is too short.

"if you only need one side of the plate, if it is iron or another ferromagnetic material, place a large ceramic magnet on the unused side, it will permanently be saturated with magnetic field."

I do not understand this.

RHABE

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#8
In reply to #5

Re: Magnets and Magnetic Materials

12/13/2008 1:48 PM

yeah its kind of complicated to explain, but its relatively simple... Iron absorbs magnetic B field... it is the only material next to another magnet, that can become saturated with a magnetic field and block a magnets field lines from penetrating to the other side. at the same time, a soft metal with iron in it will become magnetized from the pressence of a magnetic field. if it is a nickle/iron plate, for example 2 square inches... and you place a circular magnet the same diameter on one side of the plate, the plate will become saturated with magnetic fields, and depending on the thickness and amount of iron in the plate, no magnetization will "Leak" out the other side, if its 50% iron and nickle, then much of the saturation will flow out the other side, making the plate magnetic and protecting the magnet on the other side. Speaker magnets use the same principle, they are protected by iron caps, wich are extremely saturated and magnetic long as the magnet is in contact with it. the people that make speaker magnets use the iron to protect the magnet so it doesnt break, they are very brittle.

but of coarse this is completely useless if you require both side of the plate for whatever magnetic purpose you need, then you just have to get a custom magnetic sheet plate.

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#3

Re: Magnets and Magnetic Materials

12/12/2008 11:52 PM

I saw a magnet made from magnetite sand this way in a macro way. The sand was put in a container mixed with epoxy resin and then placed in a strong magnetic field. The magnet was shaped for a generator. More of a How to make a home made generator out of local materials.

Brad

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#4

Re: Magnets and Magnetic Materials

12/13/2008 7:15 AM

Hi,

the domain walls move, split and multiply to rearrange if you cut the material.

So there is no possibility to fix them to the crystal-structure.

Unfortunately.

Modern materials are still very far from complete magnetisation, so may be one day there is a material specialist or theory or by luck to find a better one.

RHABE

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#6

Re: Magnets and Magnetic Materials

12/13/2008 1:23 PM

No one seems to understand that each domain with in a magnet is a magnet and was magnetic from the moment the material was created!

No electricity or other magnetic field needed to make it magnetic, the only reason you need the powerful magnetic fields to make a normal magnet a magnet is because there are millions of those domains in random directions and polarities that cancel each other out, the powerful magnetic field snaps these into alignment.

So the first thing I am asking is it possible to use bits of magnetic material that contain only 1 domain each? Kind of like one skin cell.

Second take these domains in the billions place them on a flat surface 1 layer thick near a very week magnetic field just enough so that the same poll of every domain is laying in the same direction?

Then bond them into a solid sheet 1 layer thick give or take a little for the boding agent used?

Then to make the field strength that you need for the application you then would bond the necessary number of layers together to get the magnetic field strength that you want!

If this could be done then you could make magnets that could span miles and be of unlimited strength! And uses such as magnetic levitation rail for transportation wont have to contend with the magnetic domain alignments becoming misaligned when they are used to repel!

One more thing the magnetic fields with in the domains come from the motion of the electrons with in the atoms that make up the material not from any outside influence and unless you destroy the atoms with in those domains the field is quite permanent!

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#7
In reply to #6

Re: Magnets and Magnetic Materials

12/13/2008 1:45 PM

Actually I did. When I mentioned the magnetite composite I was using a larger Macro example.

First problem. separating the domains so they retain maximum flux density.

Second what to use to bind them into a usable form that can handle the forces involved without impairing the flux density.

Third alignment of the domain particles with maximum domain density.

Forth combining the first three into a system to create your magnets cost effectively.

No electricity or other magnetic field needed to make it magnetic.

Actually I think you will find that the domains will have to be held in place by a magnetic field to bind them and align them into the desired shape.

Brad

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#9
In reply to #6

Re: Magnets and Magnetic Materials

12/13/2008 2:06 PM

ur talking nano technology mate, growing magnets molecules at a time. it wouldnt be cost effective, because you have to use electricity to align the field, unless you use another magnet, say on a monorail, thats why they use super conducting magnets on the maglev train, eliminates resistance of the electron spin.

yeah, layers possibly could work, and if you have the electricity for miles of layers... it would have to be done with static, the tesla effect, 120,000 cycles a second at a few thousand volts... it would induce a current on the skin of the thin layers, but wouldnt penetrate, it wouldnt need to if the layers are thin enough.

no magnetic field is permanent, not even earths or the sun. if they quit spinning the field would destruct... the same goes for rare earth magnets, magnetization is from electron spin, when domains are aligned, the electrons spin in uniform and create field lines, but magnetization is a radioactive effect, over time the material wears itself out, its just not harmful to us in the strengths we commonly use. the electrons deplete, and quit spinning from the magnet, when they quit spinning the magnet is useless, take a speaker magnet and hit it with a hammer... it loses its magnetization awful quick because your violently changing the alignment and spin of the electrons.

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#10
In reply to #6

Re: Magnets and Magnetic Materials

12/13/2008 3:48 PM

Hi,

"No one seems to understand that each domain with in a magnet is a magnet"

this is ok.,

"and was magnetic from the moment the material was created!"

this is definitely wrong as domain walls move with magnetic fields, mechanical stress and temperature.

"the powerful magnetic field snaps these into alignment."

This is ok, but only a small fraction can be snapped or turned nearly 180°, the reorientation of the unwilling other domains is more difficult so needs big magnetic fields.

"to use bits of magnetic material that contain only 1 domain each"

This question is not adequate to the problem. As soon as you cut the material into pieces - in the bulk containing only 1 domain - the domains will rearrange and resize so that the multi-domain structure will show up again in the small pieces.

"Second take these domains in the billions place them on a flat surface 1 layer thick near a very week magnetic field just enough so that the same poll of every domain is laying in the same direction?"

As you will rearrange multi-domain particles, and these on rearranging change the domain size and distribution, this procedure would generate material with the same properties as the original material except if you cannot reach again 100% density.

If you can compress to relative density k, then attainable field and flux-density are bot reduced by the same factor and thus power-density by k².

"Then bond them into a solid sheet 1 layer thick give or take a little for the boding agent used?"

Very new magnetic data will come up at very thin layers (some nanometer thick). See for spintronics or GMR (giant magnetic resistivity).

Unfortunately the situation of least stored energy - the random orientation of magnetic domains - is stable and will restore the minimum-energy condition if you disturb the situation by cuts or else.

RHABE

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#11
In reply to #6

Re: Magnets and Magnetic Materials

12/13/2008 5:45 PM

Dear Brain Gain.

The domains are not a one to one correspondence with a feature of the material. That is, they are not contained, say in a single grain of ferrite.

not sure i understand what you mean when you say it was magnetic from the moment the material was created. In the case of steel, it wasn't ferromagnetic when it was austenite, only after it cooled to ferrite...

as for the fields is quite permanent, just let me take the temperature of this above say 1370 degrees F and then lets test your field strength.

sorry.

milo

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#12

Re: Magnets and Magnetic Materials

12/15/2008 2:40 AM

I don't know anything about this, but, surely: ultimately the individual magnets are atoms with electrons in orbit.

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#13
In reply to #12

Re: Magnets and Magnetic Materials

12/27/2008 11:44 PM

... ultimately the individual magnets are atoms with electrons in orbit.

True in most cases -- magnetism arises from the cumulative effect of many individual unpaired electrons in atomic orbitals. I say "most cases" because sometimes the unpaired electron resides in a molecular orbital involving a transition metal (Fe, Mn, V, Ru, Cr) complexed to an organic ligand (see "molecular magnets"). But the magnetism of an individual atom is too weak to measure. Magnetic domains contain many billions of atoms.

In any case, the idea of cutting out individual domains and arranging them by hand is probably doomed if attempted at non-cryogenic temperatures. I might be wrong about this, but I suspect that manual mechanical jostling and random thermal motion of atoms at room temperature would cause the orientation of individual domains to drift before enough them were in place to produce a stabilizing field. Bulk magnetism is produced by simultaneous collective alignment of thousands of adjacent domains. Mutual collective magnetic attraction keeps the alignment stable against the disordering effects of heat (below the Curie point) and magnetic repulsion (when like poles are forced together). Therefore, trying to build a bulk magnet by aligning domains one at a time at room temperature seems hopeless, and extremely tedious!

Sorry for the lateness of this post. I am working my way backwards, trying to catch up on my CR4 stories -- I don't want to miss interesting threads like this one.

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#14
In reply to #13

Re: Magnets and Magnetic Materials

12/28/2008 8:01 AM

welcome back svengali!

milo

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#15
In reply to #14

Re: Magnets and Magnetic Materials

12/28/2008 6:46 PM

Thank you Milo, I'm glad to be back enjoying the interesting discussions again. So nice to hear from you!

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#16

Re: Magnets and Magnetic Materials

01/07/2009 12:50 AM

The NdFeBo magnets typically use the materials powdered, compressed and heated (sintered) then use the capacitor-pulsed charge to align. The materials are then plated with nickel or gold so moisture won't degrade and they still easily shatter. Typical Curie point for most is about 80 C.

Good idea though - heck - they weren't even around 'til '83. Good lay site is supermagnetman.com? - he has made an array that has over a 1T fixed field using a magnetometer to gauge strength. I've seen a journal article where a research group ground the material finer (not as fine as domain level and not quite nano) but produced a 5 Tesla field but they had to jump through a ton of elaborate steps.

Do a search for Inductrack if you want to see an interesting application.

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#17

Re: Magnets and Magnetic Materials

01/07/2009 11:25 AM

Ok lets simplify my post....

What if you take a material that has little or no effect on a magnetic field and then form it into a shape or sheet of the size you want.....

Then riddle the material with holes 1 atom in diameter from one side to the other in a honey comb pattern that has walls thick enough to prevent the magnetic field from one cell from influencing those around it.....

Then using something like the methods used to slice off an atom or streams of atoms for experiments in cyclotrons or super collider to separate the magnetic material into single atom streams and using the a modified version of the collider to aim them into the honey comb cells instead of into each other....

The result should be unlimited length straight lines of atoms forming unlimited length single magnetic domains 1 atom in diameter far enough a part so that the adjoining domains will not ever have an effect on each other, so that the natural north south attractions with in each line of atoms will automatically align and will keep each single domain cell in alignment, and if an external magnetic force caused a misalignment with in the cell then the north south attractions should realign on there own after the external magnetic field is removed....

This way you could make magnets of any size or configuration with out the need to externally influencing the domains into alignment and all that needing large magnetic fields to magnetize the material or the temperature issue of the normal one peace magnet of today would not even apply...

And before you say it would be to costly or to difficult make take a look at the processor in you computer it is literally grown layer by layer and each new generation of chips are coming closer to their goal at Intel of making each transistor only 3 atoms in size, the cost and the process to make the item is only limited in practical purposes to which the uses and the markets that can benefit or else Intel would have been bankrupt over 25 years ago....

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#18
In reply to #17

Re: Magnets and Magnetic Materials

01/07/2009 11:39 AM

Thanks for this. Your thinking has certainly evolved on this question.

Where was the simplify part?

Seems like a complex method to me.

Good luck on your quest.

milo

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#19
In reply to #17

Re: Magnets and Magnetic Materials

02/04/2009 8:10 PM

This post has gone haywire, but Brain Gain let me help you out.

First of all, I and probably everybody else in this discussion understands what you are talking about. I will tell you a secret, this idea is used all the time in manufacturing magnets in the first place. If you have a small domain and put it next to another, they are no longer independant as these will interact. If these are close enough they will condense into a larger domain, if they are far away they will maintain 1 and 1 character. You can bring them closer, if there is a diamagnetic boundary between them, as these will limit domain-domain interactions. There is a limit to what you are doing since domains interact and the boundary takes up space (thus lowering flux). You will find that out of all the combinations of Elements and this knowledge, NdFeB lattices are probably the best at maximizing flux.

Your idea doesn't take into account that the "atom laser" will eventually need to condense into a stable lattice. This means unless if you suspend it in a hyper powerful optical lattice of somesort, you will be brought back to the need for other atoms to hold it in place (these are in a sense an optical lattice since electron communication is done through photons) and create diamagnetic boundaries (aka epoxy or however you described it). YOU HAVE TO DO ALL OF THIS FROM AN ATOMIC APPROACH if you want to maximize flux unless if you want to suspend everything in a appartus of powerful lasers. You should research the beauty of the NdFeB structures as these help maximize domain density by actually having a multilayered unit cell of different NdFeB configurations. If done correctly this has alot of possibilities in enhancing the packing of magnetic domains, one is the formation of vortices.

After all is said and done with custom nano atomic placement, it still needs to be stable.

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