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Paramagnetic Behavior: Newsletter Challenge (October 2011)

Posted October 03, 2011 10:09 AM

This month's Challenge Question:

Most materials exhibit paramagnetic behavior. So why are there so few ferromagnetic substances?

And the answer is:

Materials are formed with atoms and molecules, that form natural magnetic dipoles. In paramagnetic materials the dipoles are far apart, so they behave independently, and are randomly oriented; when a magnetic field is applied the dipoles become oriented in the direction of the magnetic field applied, but because they are far apart they do not affect their neighbors. When the magnetic field is removed, the dipoles become randomly oriented again, this is the reason a paramagnetic material is not a permanent magnet (ferromagnetic).

On the other hand, if the density of magnetic dipoles is high the dipoles interact and affect each other. The immediate neighbors will have opposite alignment and every other dipole in each row of the crystal will align to form a lattice. This creates two lattices that interact strongly (ferromagnetism). We can see that when the density of dipoles is high, the dipoles disalign their immediate neighbor and align with every other neighbor. There are very few materials with this property (high density of dipoles), so ferromagnetic materials are not abundant.

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#1

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/03/2011 11:30 AM

I think this has to do with the outer valance electron distribution about an atom (the configuration of its electron spin-state (up or down) and the configurations of those electron shells) and how the neighboring atoms in the material co-align.

If an atom's electrons order themselves such that their spin-states predominate in one direction (up or down) the atom will be magnetic.

Iron and steel atoms have the ability to maintain a polarized configuration for a long time (once magnetized), but most materials' atomic structures will not and randomize their spin-state orientation quickly once the external field is removed.

Temperature will also impact the magnetic state of a material. The lower the temperature the better the material retains its spin-state configuration.

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#2

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/04/2011 12:29 AM

I think it might have to do with the amount of substances that contain carbon.

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#3

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/04/2011 1:55 AM

This is not a suitable Newsletter Challenge. A suitable challenge might consist of combining some pieces of common knowledge (in clever or even tricky ways) to obtain a surprising or elegant result. Instead, this question depends on a lot of specialized rote knowledge about elements such as iron, or combinations such as Alnico, or involving rare earths.

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#9
In reply to #3

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/06/2011 8:16 AM

And how am I supposed to get another Episode out of this topic??! (Yes I'm still writing, intermittantly. Had a rash of life getting in the way this year...)

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#4

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/04/2011 5:43 AM

It has to do with unpaired electrons. The magnetic moment of paired electrons cancel. If the magnetic moment of the atom exceeds some threshold, the atoms self align, reenforcing the magnetic field (ferromagnetism).

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#5
In reply to #4

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/04/2011 8:42 AM

There may be some truth to that. I can't remember if the number of electrons in the valance shell is a factor. It has been awhile since I had chemistry, but I do remember that the spin-state of the electrons is what gives an atom its magnetic property. They need to predominately spin in one state (up or down) or another.

My guess is that various element's electron shell configurations/geometry play a large part in the ability of an atom to retain electrons in the same spin-state over time or be easily reconfigured.

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#6

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/04/2011 11:48 PM

why people are so chaotic?

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#7

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/05/2011 6:05 PM

I was on the verge of concurring with Tornado, until re-reading the question, and contemplating ... (my training in magnetic theory has all-along left me feeling unsatisfied, that we know about as much regarding the true "nature" of magnetic flux as we do of the true "nature" of light).


At THIS page of 'good-stuff': the proverbial 'nutshell' is in accord with what most of us know:
"At an atomic level ferromagnetism is explained by a tendency for neighbouring atomic magnetic moments to become locked in parallel with their neighbours."


Wiki takes things a smidge deeper HERE , delineating both "spin" and the "Pauli exclusion principle" as being responsible for ferromagnetic bahavior.

Still ~ I can't help but wonder-upon the ACTUAL question being posed: "WHY are there so few ferromagnetic substances?" ...

Is the OP's answer going to take us into the realm of (dying) stars and the birthing of all matter of which we know, and some facet thereof, not yet imagined...?

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#8

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/05/2011 7:38 PM

Ok how about this... Because the earth is mostly composed of iron and oxygen, both of which are paramagnetic?

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#10
In reply to #8

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/06/2011 8:57 AM

Uh...... (Mr Semantics here)...

technically-speaking, while it is true that oxygen is *paramagnetic*...

(( see (this) or (this) YouTube video...))

iron is, in fact, strongly *ferromagnetic*.

There IS a distinction betwixt diamagnetism, paramagnetism, and ferromagnetism

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#11
In reply to #10

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/06/2011 3:12 PM

Sorry, let's take the O *ut of that equation

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#12

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/16/2011 4:10 PM

Did the poster ever answer this question?

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#13

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

10/25/2011 4:16 PM

The unpaired spins in a material will swing to orient with the external field. It is always the outer electrons where this response is largest. Inner paired electrons exhibit diamagnetic response but this is generally swamped by much stronger paramagnetism. Ferro (and antiferro) magnetism are special cases that require atoms be close and with an orbital geometry that makes more favorable for the spins to align (or counter-align). This COSTS magnetic energy. It is made up for by a decrease in electrostatic energy. These produce a phase transition that has a finite latent heat and will vanish at higher temperature. This means these last two cases are rather special. Below this "Curie Temperature" they are always magnetically ordered. For ferromagnets these break up into small domains because larger domains make bigger fields and eventually the fields win and everything gives a net random orientation. When you magnetize a piece of steel you are just increasing the size of the domains pointing one direction over the other.

It is a red herring here to compare paramag with ferromag. Compare para with dia and ferro with antiferro. The last two are rare because the arrangement of such orbital in a material with unbound electron pairs that have strong enough overlapping orbitals to make this phase transition is hard to come by or be so weak that the Curie temperatures are way below room temperature. In general, materials like to form bonds that use all the available electrons and not have some unpaired ones swinging free.

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#14

Re: Paramagnetic Behavior: Newsletter Challenge (October 2011)

04/03/2012 2:46 PM

This seems to miss the point that it is electron exchange that drives ferromagnetism. The magnetic interaction is working to cancel itself but some (eg. matensitic) materials have such strong electrostatic and quantum mechanical interactions that this is overcome.

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