If we consider electrons circulating around the nucleus in circular orbits, they constitute current loops and hence have magnetic moments (due to their orbital motion). In a paramagnetic material, for example, those magnetic moments point everywhere so the net moment is zero. Turning on a magnetic field should produce a non-zero magnetic moment because it tends to align the magnetic moments with the field direction by producing torques on the orbits (or the current loops).
- First of all, how accurate is the above as a description of paramagnetism?
- Second, generally, the torque on a current loop would depend on the direction of the current. So the magnetic moments end up being either parallel or anti-parallel with the field. If this is correct, then shouldn't the application of the field have no effect on the net magnetic moment? If, before the field is on, the moments are randomly oriented in all directions, isn't it reasonable to expect that some of them would end up parallel to the field and others anti-parallel in such a way that they cancel out?
- Third, why does the fact that "the electrons in diamagnetic materials are all paired up and their spins cancel out" matter? If we're considering orbital motion, why are the spins relevant? In other words, are the magnetic properties of such materials manifested due to orbital motion or spin? (at least for the large part, which one are they produced by?)
- Fourth, following up on the last question, how does the "unpaired" electron in a paramagnetic atom contribute to its characterization as paramagnetic?