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Homework Help: Fermi Vector in Ferromagnetic Material

  1. May 2, 2012 #1
    1. The problem statement, all variables and given/known data

    Consider an electron gas of density [itex]n_{0}[/itex] in three dimensions that is completely ferromagnetic: all electron spins point in the same direction. Derive:
    a) The Fermi wave vector in terms of [itex]n_{0}[/itex].
    b) The parameter r as the radius in atomic unites that encloses one unit of charge.
    c) The average kinetic energy per electron.

    2. The attempt at a solution
    a) My attempt is to simply solve as follows
    [tex]n_{0}=\frac{k^{3}}{3\pi^{2}}[/tex]
    [tex]k=(3 \pi^{2} n_{0})^{1/3}[/tex]
    however I don't think this accounts for the fact that all spins point in the same direction. How do I account for this? Not being certain on this point of course follows through to parts b and c.

    b) I'm tempted to simply solve for r
    [tex]1 = \frac{4 \pi n_{0}}{3} (a_{0} r)^{3}[/tex]
    [tex]r = \frac{6^{1/3}}{2 a_{0} (n \pi)^{1/3}}[/tex]

    c) Same general tack but not sure how to account for the spins;
    [tex]E = \int EdEN(E) = \frac{\mu}{5 \pi^{2}} (\frac{2 m \mu}{\hbar^{2}})^{3/2}= \frac{3}{5} n_{0} \mu c[/tex]
     
  2. jcsd
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