What is the problem? With 100 years old compass still working or with blinking light bulb in the second video?

I applied the voltage on the coil-U core without the shunt, disconnected the battery and it couldn't hold the shunt. Since the remanence magnetization is not shape dependent as we know, I believe that remanence alone is not adequate to explain this phenomenon.

No problem in understanding the blinking light this is perfectly explainable by the collapsing magnetic field.

The solution to the magnetic loop enigma

Okay I've decided to give you the answer since no one here seems to know about it. The phenomenon responsible for this effect has little to nothing to do with magnetic remanence since this is too small an ineffective in this case presented to hold the structure together.

The phenomenon responsible for this effect is called circular magnetization (look it up) and is essentially the same field generated in a torus solenoid with a core electromagnet. You essentially creating a magnetic loop or else a circular permanent magnet (although very weak in our example).

One key characteristic of monoblock circular permanent magnets magnetization mode (very rare used) in contrast with other types of magnets is as soon you physically break the circle... they broken parts are not smaller individual permanent magnets (with the exception of a circular magnetic array made out by individual magnets).

You can demagnetize apart of thermal shock also by mechanical shock...and that's what I did. The closed loop configuration was magnetized by the magnetic field created by the high current passing the through the coil. The mode of magnetization is circular (not to be confused with radial) and is not detectable with a Gauss meter. Magnetism is confined inside the loop and don't leaks outside... nothing special really.

Emmanouil

Emmanouil,

You ask me to read about circular magnetization. My response is: you should also enrich your knowledge about magnetic materials. Ferromagnets are not created equal, some are soft (used for making transfomers) while others are magnetically hard (like any permanent magnet). And everything in between, especially various steels differ a lot, some of them even appear non-magnetic. The harder the magnetic materials the higher magnetic remanence they exhibit, as 'a rule of thumb'.

Besides, your categorical statement:

One key characteristic of monoblock circular permanent magnets magnetization mode (very rare used) in contrast with other types of magnets is as soon you physically break the circle... they broken parts are not smaller individual permanent magnets (with the exception of a circular magnetic array made out by individual magnets).

is simply not true. The broken parts still remain magnetized.

However, the observation that some materials can be demagnetized by mechanical shock is true. The explanation is via magnetostriction (or by piezoamagnetism if you prefer), sometimes via multiferroism. Something similar to operation of piezoelectric gas lighter generating high voltage after sudden deformation.

Dear Marek,

quote:

"

Besides, your categorical statement:

One key characteristic of monoblock circular permanent magnets magnetization mode (very rare used) in contrast with other types of magnets is as soon you physically break the circle... they broken parts are not smaller individual permanent magnets (with the exception of a circular magnetic array made out by individual magnets).

is simply not true. The broken parts still remain magnetized."

Let's put this to the test!

Unfortunately, I don't think a market currently exists for circular rare Earth monoblock magnets. These would be difficult to make and expensive without real commercial value only maybe for research strictly.

All of the domains would have to be precisely and uniformly magnetized in a circular N-S head to tail fashion and exact concentrically oriented around the center of the ring or else it would develop into a dipole ring magnet.

Actually I have in the past created a circular magnetic magnetic array consisting of 12 cube neodymium magnets in a aluminum frame.

Above figure shows how the field of a circular concentrically magnetized looks like using a magnetic viewing film. Magnetism (black areas) is only around the ring inner mass. No magnetic field inside or outside the ring (green areas).

I believe that with a monoblock mass rare Earth circular magnet when the circle is broken it will loose its magnetization and so will its broken pieces.

I will try tonight to magnetize a normal commercial axial magnetized ring ferrite magnet into a circular magnet, then break it and report back here.

Emmanouil

Very good idea. Just be sure not to use AC current to magnetize the ring . ..;).

Have a nice weekend,

Marek

You too Professor.

Circular concentric magnetization experiment

I had problems demagnetizing the ferrite with my ac demagnetizer so I had to apply a more primitive technique.

step 1:

Circular concentric magnet experiment (Step 1 demagnetization of regular ring ferrite magne

https://www.youtube.com/watch?v=yAoZo3ggkD8

step 2:

Circular concentric magnet experiment (step 2 circular permanent magnetization of ferrite)

https://www.youtube.com/watch?v=9CUmW1utQ1s

step 3:

Circular concentric magnet experiment (step 3 Breaking and testing broken parts if made magnets)

https://www.youtube.com/watch?v=Ji2KDAe9Fsk

Notes: If in any doubt that if the ferrite was circular magnetized in step 2 by the 12V high current battery watch this:

https://www.youtube.com/watch?v=rWxNlPnwHtw

Also if you believe that in step 3 the individual broken parts didn't remain as normally expected, magnets because the mechanical shock when the circular magnet was broken, I don't believe this is the case since the magnet remains paramagnetic at the center before and after it was broken.

Of course I could be wrong. Do the experiment your self.

Experiment suggestion improvement:

After step 1 demagnetization, break the demagnetized ring in two halfs and then proceed to circular magnetization step 2 with the battery to see if the two parts stick together to make sure that the magnet is now circular magnetized.

Emmanouil

Dear Emmanouil,

There is no doubt you are fascinated with magnetic phenomena. They really deserve it. But you are not alone, big number of researchers have already established many facts as well as various theories. Thus the ground is pretty solid and many practical devices using magnetism simply work as expected.

But going back to your experiment. Step 1 (demagnetization by applying high temperature, exceeding Curie temperature) is correct. Ordinary AC demagnetizing procedure didn't work? Hint: the demagnetizing field was simply too weak. Step 2 (magnetization) is questionable at least. Why don't you use winding similar to the one presented in your first figure above (titled Capture11.PNG)? The circular field generated by a current flowing in a straight wire (called Oersted field, ~1820) is much weaker than the one produced by a wire wound as in mentioned figure (assuming the same current in both cases). It is also rather far from uniform (it is a decreasing function of distance from wire), especially that you didn't assure perfect axial geometry during magnetization. The consequences are twofold: a) the magnetizing field in ferrite ring is very non-uniform and may create quite complicated magnetization, possibly even with vortices. But there is b): how do you know that your exciting field is strong enough to transform demagnetized ferrite ring in a good permanent magnet? For this your field should at least exceed the coercivity of ferrite material. Step 3 and observation of its results. First it would be better to crush the ring without any use use of ferromagnetic materials (here: pliers). Secondly we can see some weak attraction between the investigated ring and the screws. Those screws were already in contact with other permanent magnets and thus it is unclear what is the reason for the attraction between them and ferrite ring.

And finally: please don't mix paramagnets with weakly magnetized ferromagnets. Any substance at fixed temperature cannot be paramagnetic and some time later ferromagnetic.

Circular magnetization and its practical applications. Not yet, but not excluded, we'll see. Have you heard about skyrmions?

Dear Professor Marek,

Thank you, all your comments are of course valid and me myself doubt the validity of my experimental procedure. It must much improved.

I have tried initially to make a coil in the small ring magnet and the thin magnetic copper wire has blow off immediately. Therefore i used the single wire method. I know that ferrimangetic or ferromagnetic materials after demagnetization revert to paramagnetic state which is minuscule. The screws I was using are loosing their magnetization very quickly (hard iron). I have tried to stretch the cable during magnetization of ring so the ring plane becomes vertical to the cable axis to improve circular homogeneous magnetization. The coercivity value given for the ring by the manufacturer is at 2200 Oe and I believe this makes this specific ferrite a medium magnetic material with coercivity larger than soft iron. I knew that the magnetization will not be that good but I believed it would suffice for circular magnetization. I have shortcircuited the battery prior and measured a peak current over 50 Amps. The wreck I used for breaking the magnet was not magnetized. Also I broke in the same way with this wreak an other normal axial magnetized ring and it broken parts did not loose their magnetization. Therefore by breaking the circular magnet I don't believe was enough to demagnetize it due mechanical shock.

My argument remains however, that is, watching the bellow video, it is hard for me to accept that the individual nuts lost all their residual magnetism just by softly disconnecting the nuts ring. The individual nuts after the loop was broken appear to have lost all of their magnetism:

https://www.youtube.com/watch?v=rWxNlPnwHtw

Repeat the same experiment but with the nuts forming a bar magnet and you will see that the nuts remain magnetized for a period of time after separation (depending handling) . But this is not the case for the nuts loop formation. They immediately loose their magnetism after separation.

Therefore, I believe that permanent circular magnetization is not exclusively due residual magnetization left in the material but has a different explanation. The fact that you can make a circular permanent magnet with much lower magnetization than the coercivity value of the material used, is I believe a strong indication that a different phenomena is taking place here worth investigating.

Also the other funny thing is that they are no temporarily magnetized ring magnets. Circular magnetization results always to permanent magnets and is maintained as long you don't break the circle. So residual magnetism here one can say is shape dependent and also as expected ideally time independent which is a general characteristic of Br.

However, theory and practice say that residual magnetism should be independent from shape of magnet but it seem this is not the case for circular concentric magnets, I submit, it's all about the loop.

I find this peculiar.

Emmanouil

Dear Emmanouil ,

I watched the video few times. Did you notice that after breaking the ring one of the nuts seems to be repelled (1:09-1:14)? You have written: theory and practice say that residual magnetism should be independent from shape of magnet. I do not agree as I have never seen such a theory. Even if such a theory exists then it certainly deals with uniformly magnetized bodies. You seem to like fashionable phrases, so I take the liberty to use one. Namely, you don't take into account topological aspects of this problem. In simpler words: shape is important, especially when the body is not simply connected.

But let's go into details. We may think about the ring made of nuts as of two continuous metallic rings, one closer to the center of the ring and the outer one. There is a lot of non-magnetic air between them. Magnetizing field, generated by strong electric current, is much stronger at inner ring then at outer ring. For this reason, after the current pulse is off, the magnetization of each individual nut will be quite complicated. After the ring is disconnected, the magnetization configuration of all individual nuts has every right to be changed, just to approach low energy state. I can imagine that such a state is close to what you call circular magnetization, now occurring in every nut separately, with circulation direction dictated by the side nearest to the center of initial construction. In this situation the nuts seem almost demagnetized. Why not perfectly demagnetized? Again, it is due to the shape, namely polygonal shape. We observe the forces of magnetic origin, not the strength of the field generated by magnetic moments residing in nuts. This force, in turn, is proportional to the product H.grad(H) (exactly null in uniform field, no matter how strong!).

In summary: I'm pretty sure that replacing hexagonal nuts with cylindrical washers (but not necessarily with cylindrical rods!) will result in very different effects observed in this very experiment.

By the way: have you noticed that this thread has only two interlocutors? Guess why.

Last minute: watch

https://www.youtube.com/watch?v=YhiAIsJCS9Y

with experiment with nuts repeated, but now with investigation of magnetic field around magnetized ring.

Dear Professor Marek,

Awesome explanation of the phenomena, thank you!

Will give me many hours of thought.

Nevertheless, it is curious how very relatively little energy is needed to make a permanent circular magnet. Circular magnetization seems to be after all a very efficient magnetization and transfer of energy method. Unfortunately, circular magnets are pretty useless for practical applications.

Since not a dedicated scientific study exists explaining this in detail I thing it is worth further researching and may be also for a paper to come out.

Emmanouil

Dear Professor Marek Wojciech Gutowski ,

quote: "You have written: theory and practice say that residual magnetism should be independent from shape of magnet. I do not agree as I have never seen such a theory."

source: https://www.supermagnete.de/eng/faq/How-do-you-calculate-the-magnetic-flux-density

I believe that Br is only dependent on the intrinsic properties of the material and magnetization process and not its shape and is for all Neodymium magnets (N40-N42) about 1.3 T.

https://www.eiseverywhere.com/file_uploads/63356affaf81e30a2410dc337476805b_Residual_Magnetism.pdf

There is no such thing as Br. In cited formulas we should read B(z)=\mu_0 Mr ....

Yes, Mr is the intrinsic property of the material of different physical origin than the field B. And here comes the shape dependency. Look at those formulas: they are shape-dependent (and their validity is limited to the symmetry axis). On the other hand they were obtained for axially magnetized bodies what almost never happens is reality (it may happen only for ellipsoids). The last figure on cited page shows it clearly.

Emmanouil Markoulakis Yeah this is what I was working to figure out for an arc segment magnet and a super ellipsoidal cavity magnet for which I had posted my question

https://www.researchgate.net/post/Whats_the_equation_for_Bxx_y_and_Byx_y_parallel_to_the_direction_of_Magnetization_outside_the_magnet_frame

https://www.researchgate.net/post/How_is_Ms-Saturation_Magnetization_Calculated_from_Br_Hc

Marek Wojciech Gutowski How can i go about solving the same for the Arc segment magnet and Super Ellipsoidal cavity magnet

Hello Senthil Ram Nagapillai Durairaj ,

Interesting calcualtions.

You can use this excell sheet here to automatic calculate the values for B(z) at different distances, magnets grades and for various magnets geometry:

https://media2.supermagnete.de/docs/supermagnete_flux_density_eng.xls

For clacualations away the magnetization axis z-axis on symmetrical magnets, I thing the most convenient is to use a a s/w application like this here:

http://www.femm.info/wiki/HomePage

or wolfram alpha:

https://www.wolframalpha.com/examples/science-and-technology/physics/electricity-and-magnetism/

For the super ellipsoid cavity calculations should not be that different from the arc magnet. A good approximation for the far field of this magnet , besides your very good patent,

Patent SUPER ELLIPSOIDAL CAVITY MAGNET FOR CLAW POLE ELECTRICAL MACHINE

I believe is this paper:

Article Magnetic field calculation of claw pole permanent magnet mac...

Just one question for you?

In your attached in your previous message calculations pdf for the arc magnet you calculate in a value Br=0.42 , where did you find this?

You assume a ferrite Y35 grade magnet?

Look at this table here:

https://www.supermagnete.de/eng/data_table.php

Br is not depended on geometry of magnet but only on physical material properties and magnetization process applied.

Kind Regards,

Emmanouil Markoulakis

Technological Educational Institute of Crete

Also for magnetic scalar potential calculations use this:

https://www.wolframalpha.com/input/?i=magnetic+scalar+potential+of+a+rectangular+bar+magnet&lk=3

or current loop:

http://demonstrations.wolfram.com/MagneticFieldOfACurrentLoop/