When I started to study magnetostatics it was said that magnetic fields are created by charges in motion, that is, they are created by currents. On the other hand, we have magnets and those have magnetic fields associated with them. In truth the magnetic field is such that the field lines connect the two poles. But on the case of magnets, there is no current.

So how is the magnetic field of magnets created if not by currents? How dos it relate to the magnetic field created by currents and given by Biot-Savart law?

  • $\begingroup$ I took the liberty of editing your question to correct a few grammatical errors and make it a little clearer. $\endgroup$ – wltrup May 8 '15 at 19:58
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    $\begingroup$ There is a current inside the atoms of the permanent magnet, but you would need quantum theory to understand the details. Thanks for asking, by the way. I remember driving my ninth grade physics teacher crazy with that question for almost an hour before I gave up. He gave me the same answer: there is a current inside the atoms of the permanent magnetic material, but you will need to learn quantum mechanics to understand how that works. :-) $\endgroup$ – CuriousOne May 8 '15 at 21:45
  • $\begingroup$ @CuriousOne, thanks for the comment. This current is due to the motion of electrons around the nucleus? I'm currently starting to study quantum mechanics. Indeed I'm taking one course on electrodynamics and another on introduction to quantum mechanics at same time. Could you expand your comment into one answer saying how this really works out? $\endgroup$ – user1620696 May 9 '15 at 0:17
  • $\begingroup$ The orbital angular momentum of electrons is one component, the other one is the spin of the electrons, which gives rise to a magnetic moment of each electron. The two combine to an atomic magnetic moment and the magnetic moments of many atoms in a solid can combine to a really strong macroscopic field. There is also a magnetic moment of the nuclei, but it's much smaller than that of the electrons. Where that comes into play is in magnetic resonance imaging and for chemical analysis. If you are taking a QM class now, then you will have the tools to understand magnetism very soon. $\endgroup$ – CuriousOne May 9 '15 at 0:21
  • $\begingroup$ Now, I could expand further on this, but the truth is that I hate magnetism. If you take a look at physik.tu-dresden.de/~timm/personal/teaching/thmag_w09/… you may probably get an idea why... :-) $\endgroup$ – CuriousOne May 9 '15 at 0:27

In permanent magnets the magnetic moments of the atoms is 'frozen'. To get such 'freeze' for designed materials one use materials with big magnetic dipole moments. Usually they grind such material to powder and press them in a strong magnetic field. So one use an electromagnet to design permanent magnets.

To get a magnetic field one use a coil. Electrons get accelerated - even with constant current - because they had to follow the curved wire and any radial motion is an acceleration. Last step is to understand why electrons in the case of acceleration produce a magnetic field. This happens because every electron has a magnetic dipole moment and a spin, connected unique to each other. The electrons spin get aligned - by the same way as every gyroscopic or any other rotating body - in revolution. If the spin is aligned, the magnetic dipole moment is aligned too. You get a magnetic field.

Sketches of the electrons spin and magnetic dipole moment see this question.


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