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Magnetism question

  1. Sep 8, 2005 #1
    silicon atom has 14 electrons with 2 unpaired electrons in 3p orbital.
    why silicon is not magnetic? :confused:
  2. jcsd
  3. Sep 9, 2005 #2
    Hi, Sniffer,
    It is true that the pair of 3p electrons that are spinning in the same direction are not exactly HUP since their axes are perpendicular to each other because of the vector cross product, i.e., one is along the x-axis and the other is along the y-axis.
    It is also a fact that there are three 3p electrons in phosphorus and the added electron that is also spinning in the same direction will arrange its axis along the z-axis. Silicon has valences of +2, +4, and -4; Phosphorus has +3, +5, and -3. That may have something to do with atomic magnetism. Cheers, Jim
  4. Sep 9, 2005 #3


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    Having unpaired electrons is not what makes something (ferro)magnetic, although, it is a necessary condition (ie : it is not a sufficient condition). On the other hand, the lack of unpaired electrons is a sufficient condition for diamagnetism. And, having a large number of unpaired electrons (3 or more) is likely to make a material paramagnetic (exception being Bi, and perhaps a few others that I'm not aware of).

    Ferromagnetism : http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
    Last edited: Sep 9, 2005
  5. Sep 9, 2005 #4
    Shouldn't this be about the different kinds of magnetic interactions between atoms ? I mean, after all, it are these interactions that "decide" whether a material is diamagnetic (ie generalization of Lenz's law) or paramagnetic (ferro, ferri or antiferromagnetic under a certain transition temperature)?

  6. Sep 9, 2005 #5


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    Not really. Paramagnetism and diamagnetism (unlike ferro, ferri and antiferro-magnetism) are not many-body effects and their susceptibilities can be calculated pretty well from the single atom case (perhaps incorporating corrections from crystal fields).

    I know of no case where say, a paramagnetic solid becomes diamagnetic upon melting into a liquid (which is not to say that such a thing doesn't exist - only I'd be pretty surprised if it did).
    Last edited: Sep 9, 2005
  7. Sep 10, 2005 #6
    i thought paramagnetism might be many body effects?? diamagnetism is clearly not.

    i read a book which says the orbital 3s2 and 3p2 can form hybrid orbital. This orbitals (when Si atoms are put together in crystal) can either form bonding or anti-bonding configuration.

    i include the image from the book here.

    it further says that the orientation of this hybrid orbitals that causes paramagnetism. is it correct? can anybody explain?

    Attached Files:

    • si.JPG
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  8. Sep 10, 2005 #7
    I know, but that was not the point. I was talking about looking for a classification of magnetic systems and how you can see what is what based upon electronic configurations.

    Neither do I

  9. Sep 10, 2005 #8
    paramagnetism is a many body effect.
    iron when heated up to its crtitical temperature will become paramagnetic of course.

    paramagnetic is in fact due to orbital overlap!
    when one unpaired orbital of an atom overlaps with its neighbouring atom, these two unpaired orbital will merge into single wave function and pauli exclusion principle applies. thus if one spin up, the other will be spin down, and the magnetism cancels.

    if suppose there are two unpaired orbital in each atom you will end up with:

    atom1 atom2 atom3 atom4 etc...
    ud du ud du ud...

    so pauli exclusion applies within an atom and among orbital overlaps as well.
    you can find this in many books on magnetism.
  10. Sep 10, 2005 #9


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    How is this an illustration of a many-body effect ?

    What you've done here, is crudely (because there are errors) describe anti-ferromagnetism (not paramagnetism), which is, in fact, due to orbital overlap. But if you still insist that paramagnetism is due to orbital overlap, please explain to me how you have paramagnetism in dilute gases ?

    What is an "unpaired orbital" ?

    If u and d refer to two unpaired electrons, then by making them be of opposing spins you are violating Hund's first rule, and hence are NOT constructing a "legal" ground-state. What you've constructed is a fictional ground state.

    Please name one such book, with the page number where I will find this.
    Last edited: Sep 10, 2005
  11. Sep 11, 2005 #10


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    Are we all talking about isolated, freely floating Si atoms, or Si in solids? Those two are two entirely different situations. If one is asking why Si crytals are not magnetic, then the crystal structure and bonding of all those Si atoms is THE crucial ingredient in this question and cannot be ignored.

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