Cause of diamagnetism

  • Thread starter A Dhingra
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  • #1
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Can any one explain what is the cause of diamagnetism....

to the extent i know is that the paired electron with opposite spin cancel out each other's magnetic moment....
is there something more to this...?

and on application of external magnetic filed why does it repel it....

thanks for any help...
 

Answers and Replies

  • #2
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it appears to just be a (very surprising and odd) fundamental property of electron pairs.

ordinarily one would expect any magnet to align with not against an external field.
 
  • #3
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it appears to just be a (very surprising and odd) fundamental property of electron pairs.

ordinarily one would expect any magnet to align with not against an external field.
true it is a property .......
but there must be some explanation that it repels....

as far as i know , it is that the paired electron has net magnetic moment =0, but when an external field is supplied then the field of electron that points the same direction as the supplied one will observe an increase in its velocity and other's velocity decreases...... hence magnetic field is created....

i think the magnetic field strength set up in the substance should be of good value( Bext - B elctron) ..... and appears to be in the direction of the supplied field...

plz tell me about it ........if u know.......
 
  • #4
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http://en.wikipedia.org/wiki/Diamagnetism
A superconductor acts as an essentially perfect diamagnetic material when placed in a magnetic field and it excludes the field, and the flux lines avoid the region

Superconductors may be considered to be perfect diamagnets, since they expel all fields from their interior due to the Meissner effect. However this effect is not due to eddy currents, as in ordinary diamagnetic materials
I guess the effect you describe might be responsible for 'ordinary diamagnetism'.


http://en.wikipedia.org/wiki/Zeeman_effect
 
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  • #5
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as far as i know , it is that the paired electron has net magnetic moment =0, but when an external field is supplied then the field of electron that points the same direction as the supplied one will observe an increase in its velocity and other's velocity decreases...... hence magnetic field is created....
but even if it was then why doesnt the resulting electron pair simply flip around.
It should be unstable
 
  • #6
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true it is a property .......
but there must be some explanation that it repels....
I think you are just wrong about this.
Some properties are just fundamental
 
  • #7
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Why don't the spins alternate and thus cancel? I vaguely recall that it has to do with the spacing of the atoms. The potential energy curve there adds a factor which makes the "magnetic domain" of aligned spins energetically favorable under a narrow set of conditions.
 
  • #8
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but even if it was then why doesnt the resulting electron pair simply flip around.
It should be unstable
actually you are correct the atom should become unstable...............
but it seems this does not happen , do you know why..?

i would like to discuss the cause of diamagnetism in a proper manner please.( is this way of asking for a discussion is fine) ....
 
  • #9
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why don't the people of science accept that if they created a term and are unable to describe it properly then it doesn't mean it cannot be described...
please , good excuse but i cannot accept it....
fundamental , but still can be questioned.....
 
  • #10
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Why don't the spins alternate and thus cancel? I vaguely recall that it has to do with the spacing of the atoms. The potential energy curve there adds a factor which makes the "magnetic domain" of aligned spins energetically favorable under a narrow set of conditions.
please if possible can you be more descriptive about what you are saying...
i could not understand it....
 
  • #11
DrDu
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Consider a helium atom. Both electrons sit in the 1 s orbital. According to the Pauli principle, they can only do so because they have different spin. To flip one spin around would necessitate lifting the electron to an electronically excited state which would cost many electron volts of energy; far more than that gained by the reduced repulsion with the magnetic field.
 
  • #12
DrDu
Science Advisor
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The magnetic field induces an electric current in the diamagnetic molecules. It has nothing to do with the spin of the electrons but with the orbital magnetic moment of the electrons. The sign is the same as that of induced currents in classical electrodynamics where repulsion also occurs, see:
 
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  • #13
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Consider a helium atom. Both electrons sit in the 1 s orbital. According to the Pauli principle, they can only do so because they have different spin. To flip one spin around would necessitate lifting the electron to an electronically excited state which would cost many electron volts of energy; far more than that gained by the reduced repulsion with the magnetic field.
ok so considered a helium atom,with its electron moving with opposite spin, then how does application of magnetic field causes formation of opposite magnetic filed....

and as you said is it really possible to change the spin......
ya i remember , in chemistry ..... we at least observe in the book........ every time any compound say NaCl is formed from Na and Cl atoms ..........
 
  • #14
DrDu
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When the atoms are brought into a magnetic field the changing magnetic field leads to an electric field (Faradays law of induction) which induces a current. As the electrons are already in their quantum mechanical ground state, this current does not decay, in contrast to the situation in classical mechanics. This current is the source of the repulsive magnetic field.
 
  • #15
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hi ...
ok so by far i understood that the electrons are in their ground state ,and the induced current due to the changing magnetic field does not decay...
remains for long .... hence what i can interpret out of this is that current will remain constant so the magnetic field ( net ) should continue to exist ....but the effect is gone as soon as the magnetic field is removed....
so where is the error in this interpretation.....

please do explain.....
 
  • #16
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I haven't seen Lenz's Law discussed in this post. Lenz's Law is foundational to explain diamagnetism.
The external magnetic field induces a current in the orbiting e- in such a way that the magnetic field produced by the e- opposes the direction of the external field. Hence the repulsion force and the negative magnetic susceptibility value for all diamagnetic material.
 

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