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How Do Magnets Work At an Atomic Level (Motion of Charged Bodies)?

  1. Mar 27, 2012 #1
    I'm a year 12 physics student and I have a keen interest in the inner workings of a magnet.

    I know that magnetic fields are created by the motion of charged bodies.
    1. Is this somehow related to the how magnets create their fields, within their structure at an atomic level?

    I've heard that the magnetic fields created by magnets are associated with the "spin" of charged particles within the atoms of the magnet.
    2. What kind of magnetic fields do spinning charged bodies create in motion? When stationary?
    3. What does this have to do with the magnetic field of a magnet?

    I know that each atom within a magnet acts as a microscopic dipole and these are all aligned within a magnet.
    4. So how exactly do these atoms act as dipoles?
    5. How are the charged bodies within a magnet's atomic structure moving when these dipoles are said to be "aligned"?

    I know that there is some quantum physics involved in understanding these but I will try my best to interpret any answers I'm given, so please don't hold back. Thank you.
     
    Last edited: Mar 27, 2012
  2. jcsd
  3. Mar 27, 2012 #2

    K^2

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    All of this boils down to nature of spin. You can picture this as electrons being charged spheres that spin around their own axis. It's not entirely correct, but until you get into quantum mechanics of it all, it's not a bad mental picture to have. If you have a spinning charged object, you end up with a current loop, same as if a bunch of point-charges were traveling in circles making up a sphere together. So each individual electron acts as a tiny magnetic dipole. The rest is pretty much as you say. If all of these dipoles align, their magnetic contributions add together, generating an overall magnetic field.
     
  4. Mar 27, 2012 #3
    In order to understand magnetic materials (as opposed to electromagnets) you need quantum mechanics.

    Atoms with partially filled shells can carry a magnetic moment without any moving charges in the classical sense. The magnetic moment you see is generated by the electrons. The nucleus may also carry a magnetic moment, but in almost all cases that can be neglected (it is about 2000 times smaller than that of the electrons).

    The magnetic moment has two components, called "spin" S and "orbit" L.

    The spin is a purely relativistic effect. Each electron has spin S=1/2.

    The orbital moment has integer values that can go up to L=3 in rare earths and actinides.

    When you have several electrons, then there are rules of how to combine their spin and orbital moments. They are called "Hund's rules". You end up with a total magnetic moment quantum number J. The atom's magnetic moment is this quantum number multiplied by a "Lande factor" g. For spin-only (L=0), g=2, for orbit-only (S=0) g=1. If you have both spin and orbit, it is somewhere in between.

    http://en.wikipedia.org/wiki/Hund's_rules
    http://en.wikipedia.org/wiki/Landé_g-factor

    One you have several (potentially) magnetic atoms in a crystal lattice things become ... interesting. You get interactions between them Hund's rules may be modified by crystal fields, ... Some of this is still the subject of ongoing research.
     
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