Larmor precession and magnetic ordering

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Homework Help Overview

The discussion revolves around the concept of Larmor precession in the context of atomic magnetic moments and their behavior in ordered magnets, particularly ferromagnets. The original poster reflects on the apparent absence of Larmor precession in these materials and questions whether magnetic moments are frozen due to interactions with crystal fields or if they precess in unison.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the relationship between magnetic ordering and Larmor precession, questioning the effects of crystal field interactions and symmetry breaking on angular momentum. There is an inquiry into how these factors influence the behavior of magnetic moments.

Discussion Status

The discussion is ongoing, with participants providing insights into the implications of broken rotational symmetry and its effects on angular momentum. Some guidance on the relationship between symmetry and magnetic behavior has been offered, but multiple interpretations are still being explored.

Contextual Notes

There is a mention of the original poster's uncertainty regarding symmetry breaking and its implications, indicating a potential gap in understanding that is being addressed through the discussion.

DeathbyGreen
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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.
 
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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.
 
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.
 
Yes, that is in cubic symmetry. Angular momentum is not a good quantum number unless there is rotational symmetry.
 
DeathbyGreen said:
I never hear about larmor precession anymore
Ahh...Magnetic Resonance Imaging owe's its existence to this!
 

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