# Quick question regarding Larmor precession and bar magnets

I was just reading a bit about magnetic dipole moments, Larmor precession, angular momentum etc., but there was one little thing that was bothering me. As far as I know, any angular momentum will precess around any magnetic field, no matter how big the angular momentum and the magnetic field is. So the angular momentum can be as small as you like. So then I thought about bar magnets, which I thought had a very tiny amount of angular momentum due to their magnetic dipole moments, for as we know, the magnetic dipole moment is the gyromagnetic ratio (gr) times the angular momentum. But of course, the gr is really big for bar magnets because it's so large for electrons (and as we know, it is the electrons that make up the currents that are creating the magnetic field of the magnet). Thus, the angular momentum of bar magnets must be microscopically small. But again, as I said, any angular momentum will do, meaning that bar magnets should actually precess. What is wrong with my thinking here?

• It's not clear to me what you're asking about. You're aware that Larmor precession is a quantum mechanical phenomenon? It is something that happens to nuclei/particles with angular momentum some multiple of $\hbar/2$, although in the case of NMR/MRI scans the bulk magnetization of an object shows the Larmor precession of all the atoms together. Do you want to know about the classical Larmor-precession like wobble of an entire magnet suspended in an external magnetic field? Or do you want to know how all the atoms will oscillate if you can manage to misalign them with the field? (how NMR works) Commented Jan 31 at 18:22

The magnetization in a bar magnet is due to the alignment of the spin magnetic moments of the electrons, not to currents. The precession would depend on the cross product $$\mu\times{\bf B}$$. Since $$\mu$$ is aligned along $$\bf B$$, there is no torque and no precession.
• I thought you were asking if the bar magnet would precess due to its own magnetic moment and angular momentum. If $\mu\times{\bf B}$ Is not zero, there will be a torque. The magnet would precess if it had a large angular momentum, but if the angular momentum is small (as in the case of a bar magnet), it would just rotate to align with the magnetic field as a compass needle does. A gyroscope precesses is because it has a very large angular momentum. Commented Jul 16, 2020 at 9:50