Larmor precession and magnetic ordering

[DeathbyGreen]

Homework Statement

When we speak about Larmor precession we refer to atomic magnetic moments precessing in a magnetic field. In ordered magnets, such as ferromagnets, I never hear about larmor precession anymore. Are the magnetic moments frozen due to interactions with the surrounding crystal fields? Or all the moments precessing in the same direction? This isn't a homework question, just one I was thinking about and unable to find a good answer for.

 

[PietKuip]

Indeed. The moments do not even need to be ordered. In a compound, the rotational symmetry is broken, and this often leads to the angular momentum being quenched.

 

[DeathbyGreen]

By rotational symmetry being broken, do you mean that the crystal field interaction forces the eg and t2 orbitals into different energy levels? I'm not to familiar with symmetry breaking but I'll try and read into it.

 

[PietKuip]

Yes, that is in cubic symmetry. Angular momentum is not a good quantum number unless there is rotational symmetry.

 

[DeldotB]

I never hear about larmor precession anymore

Ahh...Magnetic Resonance Imaging owe's its existence to this!