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Electrons have magnetic dipole moment. This magnetic moment will be influenced in an electric field in case the electron get moved non-parallel to the current. The magnetic moments will be more or less aligned. During the movement of an electron in a wire under the influence of an electric potential, the electron has a chaotic movement, in addition to a drift velocity along the wire.

What is the sum of the magnetic moments after such a walk? Consider only some straight length of the wire, not the electrons "at rest" in the source and in the sink.

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  • $\begingroup$ The way you phrase this question - in particular the second paragraph - I wonder if we are looking at a homework problem? In which case, the site policy requires you to (a) tag it as such, and (b) show what specific part of the problem you are having a problem with. Is there an underlying physics concept you need a better explanation for? You have two possible energy states - aligned, and misaligned. The energy difference is related to the product of spin and electric field; and the system attempts to remain in thermal equilibrium, so Boltzmann comes in somewhere... $\endgroup$ – Floris Sep 5 '14 at 3:57
  • $\begingroup$ @Floris Perhaps questions in learning books are on the level of no native speakers? :-). Seriously the question is my own. $\endgroup$ – HolgerFiedler Sep 5 '14 at 4:22
  • $\begingroup$ I did consider that possibility - which is why I said "I wonder"... Does the hint in my earlier comment help at all? $\endgroup$ – Floris Sep 5 '14 at 4:24
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The magnetic moment of an electron is associated with its spin angular momentum. In the absence of a spin-orbit sort of interaction to transfer angular momentum from the mechanical degree of freedom (the electrons go around the circuit) to the spin degree of freedom, the electrons in a current-carrying wire will be unpolarized and the their net magnetic moment will be zero.

I did recently learn about half-metallic ferromagnetics, materials whose band structure conspires to make them conducting for one electron polarization and insulating for the other.

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  • $\begingroup$ Sorry for late response. I hoped to see more opinions. I agree with your answer. My question pointed to the phenomenon that near a current carrying wire a magnetic field could be measured. From your answer I see that the electrons are not responsible for this field. Later I ask, would it be possible that the measurement induces the magnetic field. $\endgroup$ – HolgerFiedler May 16 '15 at 7:23
  • $\begingroup$ physics.stackexchange.com/questions/173344/… $\endgroup$ – HolgerFiedler May 16 '15 at 7:29

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