Yes it is true and this is really mysterious i think...

https://terpconnect.umd.edu/~wbreslyn/magnets/is-nickel-magnetic.html

Because it is not all nickel or copper and the magnetic properties of the alloy does not exhibit magnetic properties.

Yes I agree but I'm asking for a correlation with the second part of the question if the dominant magnetic behavior of nickels coins (75% cooper 25% nickel) is diamagnetic why then a pipe made out of melted nickels will not exhibit any Lenz effect similar to the one shown in the above video with an aluminium (paramagnetic) pipe?

As a side note. Regarding both dimes and quarters, are made out mainly of copper (diamagnetic) and a copper-nickel alloy. Nevertheless, copper is the dominant material here and is coated all over the surface of these coins therefore the relative strong Eddy currents will interact with a moving magnet (Lenz effect) although these coins are not ferromagnetic.

Also, pennies although only 2% in copper of total mass, are copper coated on surface and inner bulk is zinc. This is enough again to produce the relatively strong Eddy surface currents needed for the Lenz effect when interacting with a moving magnet. Both copper and zinc are diamagnetic material and not ferromagnetic. Zinc is also actually more conductive to electric currents than nickel is and therefore more likely to Eddy currents and the Lenz effect. As a side not, one of the relatively worst metal electric conductors is lead. Although diamagnetic due its bad electric conductivity it is almost immune to Eddy currents and Lenz effect. A lead pipe will produce almost zero slow down on a magnet falling through it.

The answer to the questions why "nickels" (the US 5 cents coin) are not attracted by a magnet although Ni nickel element is ferromagnetic and why a metal pipe made out from melted "nickels" will not exhibit the Lenz effect with by dropping through the pipe a magnet as it would be the case with an aluminium or copper pipe, is quite simple and two fold:

1) First, because "nickels" are made out from 75% copper Cu and only 25% nickel Ni, diamagnetic effect of these coins due to the copper is much stronger than ferromagnetic attraction of nickel material on the coin. Therefore, US nickels coins are not attracted to a magnet.

2) Secondly, although Nickel element Ni is a conductor of electricity, it is relatively to aluminium and copper, a bad conductor. Almost 3-4 times less conductive than copper. A metal pipe made out of melted "nickels" coins will consists from 75% copper and 25% nickel with all the nickel material forming the surface of the made pipe and the copper forming the main bulk of the pipe (not an alloy) since cooper has a larger molecular weight than nickel element. So you will get a shinny pipe with the nickel on the surface and copper below. Since Eddie currents which are responsible for the Lenz effect are surface currents they would normally flow on the surface of our pipe. However, since nickel element is a relatively bad electrically conductive metal it is quite immune to Eddie currents formation and therefore our "nickels" made pipe will not exhibit the desired Lenz effect of a magnet falling slowly through the pipe.

In Ni(1-x)Cux alloys the Ni 3d spin-down band possessing 0.6 holes per atom will be filled when x=0.6 and magnetization will be zero.

Dear Professor I. G. Deac,

Thank you for your expert material science answer. It couldn't be more specific.

Kind Regards,

Emmanouil Markoulakis

TEI of Crete

A static force between a magnet and a piece of metal will reveal the magnetic susceptibility of the metal (but not its electrical conductivity). Lenz effect will evidence the ability to induce eddy currents in the metal so its low resistivity if the induced currents produce visible coupling. The size and magnetisation of the magnet and the thickness of the metal are also important parameters. In alloys such as NiCu, the magnetic and electrical properties are not the average of the magnetic and electrical properties of elemental Ni and Cu. Atomic disorder in alloys usually increases ressitivity and the magnetic properties depend on the filling and modification of the band structure.

Dear Dr. L. Ranno,

Thank you for your expert input.

One question more please.

On my question I ask also how a pipe welded form melted "nickels" will react to the Lenz effect in contrast to the observed above video with an aluminium pipe.

I assumed that the metal sheet produced by the melted "nickels" after cool down in a pool would be no an NiCu alloy anymore but would consist from two distinct layers, a shiny nickel surface with the cooper layer underneath.

If we would bend this sheet to a tube (i.e. pipe) with the nickel surface on the inside of the tube, would that not further increase the resistivity to eddy currents and further negate the Lenz effect than the other case where the the tube would be in its entirety be a NiCu alloy ?

Kind Regards,

Emmanouil Markoulakis

Technological Educational Institute of Crete

Greece

Dear Emmanouil ,

you are discussing two rather different things connected to either magnetic or electrical properties. As explained by prof Deac, the dilution of ferromagnetic Ni by diamagnetic Cu to 25% of Ni will produce non-ferromagnetic alloy that will be not visibly attracted by a permanent magnet. In principle in a magnetic field gradient the paramagnetic materials are attracted to higher field and diamagnetic expelled from it, but due to the small absolute value of susceptibility of these two types of materials the resulting forces are rather weak.

On the other hand the Lenz effect has nothing to do with the magnetic properties of the tube - the higher the conductivity of the tube, the higher the induced eddy currents induced by the moving magnet inside.

The electrical conductivity of the CuNi tube wil depend on the conditions of preparation, but your idea of two distinct layers produced by "cool down in a pool" (your words) is rather unrealistic.

Sincerely

Karel Zaveta

Dear Dr. Karel Závěta ,

Thank you for expert info you have provided.

I agree with you in all points you have presented. This is my 11years old daughter's science project and instead of giving here a straight answer I've asked here to search in my computer (permanently logged in RG) for the best scientific answer she could understand and explain it to me after. Hopefully she will find this thread here :) Excuse me for using layman's terms (i.e. pool bath) in my effort not to turn this discussion in a hydrometallurgy topic which would confuse her.

Of course the Lenz effect observed of the included video on this thread would be minimized or negated if the tube was made from cupronickel alloy the same metal used in today's nickels US coins (75% copper with 25% Nickel) due to its relative bad conductivity to electricity compared to say copper and the formation of strong Eddy currents will be minimized and therefore the slowing down fall effect of the magnet through the tube will not occur or will be not noticeable.

(what follows is not suitable for my daughter's science project)

However, the twist I was trying to give to my question in this thread here is what would happen if instead of the NiCu alloy, the nickels were made of copper 75% and pure nickel coated on the surface with 25% of the total mass?

In my opinion the possible outcomes will be the following:

1) The tube has now become ferromagnetic and the magnet would now stick on the tube and not fall inside.*

2) The falling magnet creates Eddy currents with a skin effect depth located at the copper layer of the tube and therefore the Lenz effect (i.e. slow magnet fall) will be observed (assuming small distance of the magnet from the copper).

3) The falling magnet creates Eddy currents with a skin effect depth located at the pure nickel surface layer of the tube and therefore the Lenz effect (i.e. slow magnet fall) will NOT be observed.

4) Any combination of 2&3.

In the above thought experiment I believe (1) is the correct answer given this data.

Kind Regards,

Emmanouil Markoulakis

* as a side note, also if nickels US coins were made in that way (i.e. Ni surface coated with copper core) instead of an NiCu alloy, they would be attracted by a magnet in my estimate.

Dear Emmanouil,

The reason is quite subtle because it doesn't follow the Stoner's criterion having

I D(EF) < 1

Where I is the Stoner parametere and D the electronic densitity of states. In the 5 cent coins there is a good retio for avoiding the Stoner's criterion, there is 75% of Cu (good metal) and 25% Ni. A good reference for seeing the density of states of these metals a

W. E. Spicer, Cu, Ni, Ag, and Fe Densities of States

Journal of Applied Physics 37, 947 (1966); https://doi.org/10.1063/1.170853