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What is magnetism on a particle level?

  1. Sep 2, 2011 #1
    What exactly is magnetism on a particle level? I'm currently doing physics at school and we are doing a unit on electricity and magnetism.

    I can ACCEPT that a magnet has two poles and like poles repel and unlike poles attract. I can ACCEPT that a wire carrying current produces a magnetic field and I can accept that magnets can induce an electric current in a wire, but I don't actually KNOW what is going on.

    I am the kind of person that finds things like this hard to accept. It greatly enhances my knowledge and understanding of the topic to actually KNOW what is going on. I suppose this is why I found nuclear physics quite enjoyable; it answered a lot of questions I had and gave me a greater understanding of particles and how they interact in different circumstances.

    But magnets, jeez. I will tell you what I think I know now anyway, just to see if I actually already have some kind of understanding.

    So ferromagnetic materials (iron, nickel, cobalt) are magnetic yes? And this is because they have a certain atomic structure (it is to do with their electrons). So in a magnetic material there are mini magnets composed of dipoles everywhere (but I don't actually understand what these are, what they are composed of or how they align in the material).

    I know that if I put a wire carrying current near a ferromagnetic material it will become magnetised, and from what I know this is due to the poles re-aligning in the material so that the north poles in the material are attracted to the south poles of the field (I think).

    But, what I don't understand is what actually happens when something becomes magnetised? Are electrons being moved in the material? How does the magnetic field cause this action on the material (is it to do with electrons or charges)? What causes the attraction force between opposite poles of a magnet? Also, how does a material become permanently magnetised, unlike when you create a simple electromagnet using an iron nail and a AA battery?

    If anyone can help answer my questions and aid my understanding I would be very grateful (Note: I like to see things visually so if you have any diagrams they would be especially helpful).

    Thank you very much for your time!
  2. jcsd
  3. Sep 2, 2011 #2
    Charges that move produce a magnetic field, such as with electrical currents in wires. Every atom has charged electrons orbiting about inside, therefore creating magnetic fields.
    As a introductory visualization (with limited validity), picture an electron as a small charged ball following a circular path around the atomic nucleus. This is equivalent to a circular loop of wire carrying a current, which creates a magnetic dipole. Use the right-hand rule and curl you fingers in the motion of the electron and your thumb will be pointing where the effective magnetic north pole exists.
    If there are the right number of electrons in an atom (a filled shell), the magnet fields they create due to their motion cancels out and the atom is not magnetic. If the electrons are not paired right, then not everything cancels, and their is a net magnetic field that the atom generates. Each atom acts like a little dipole magnet. If they are lined up and frozen that way, you have a permanent magnet.
  4. Sep 2, 2011 #3
    Thank you for your response chrisbaird!

    So each atom in a magnetic substance acts like a small magnet itself. So does this mean that for the whole material to be magnetic that the north and south poles of each atom line up with the respective poles they are attracted to (north for south pole and south for north pole) of other atoms in the material? Like this:

    Each (N - S) is one atom and the N[ ]S is the whole magnet

    N[(N - S) (N - S) (N - S) (N - S) (N - S)]S
  5. Sep 6, 2011 #4
    Yes, that's the general idea. They don't have to line up exactly, just enough to have some non-random ordering and thus a net field.
  6. Sep 6, 2011 #5


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    That is pretty much the idea. A ferromagnetic material has very small "grains" in it that are groups of atoms that are aligned with each other. When not magnetized, most of the grains are oriented randomly and generally cancel each other out. When you apply a magnetic field of sufficient strength the grains orient themselves with the field and once you remove the field most of the grains stay aligned, as do the atoms of course, and thus you have a permanent magnet.
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