Larmor precession and magnetic ordering

In summary, the conversation discusses Larmor precession in relation to atomic magnetic moments in a magnetic field. It is noted that in ordered magnets, such as ferromagnets, there is no mention of Larmor precession due to the frozen state of the magnetic moments caused by interactions with surrounding crystal fields. However, in compounds where rotational symmetry is broken, the angular momentum is often quenched. The concept of rotational symmetry and its relation to Larmor precession is further explained.
  • #1
DeathbyGreen
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16

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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  • #2
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.
 
  • #3
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.
 
  • #4
Yes, that is in cubic symmetry. Angular momentum is not a good quantum number unless there is rotational symmetry.
 
  • #5
DeathbyGreen said:
I never hear about larmor precession anymore
Ahh...Magnetic Resonance Imaging owe's its existence to this!
 

FAQ: Larmor precession and magnetic ordering

What is Larmor precession?

Larmor precession is the phenomenon of a spinning magnetic object, such as an electron, precessing or rotating around an external magnetic field at a specific frequency. This frequency is known as the Larmor frequency and is proportional to the strength of the magnetic field.

How is Larmor precession related to magnetic ordering?

Larmor precession is closely related to magnetic ordering, as it is one of the fundamental processes that governs the behavior of magnetic materials. In a material with magnetic ordering, the magnetic moments of individual atoms or particles align in a specific pattern, and Larmor precession is what allows these moments to maintain their alignment in the presence of an external magnetic field.

What factors affect the Larmor frequency?

The Larmor frequency is affected by the strength of the external magnetic field, the mass and charge of the spinning object, and the strength of the object's magnetic moment. Additionally, in some cases, the Larmor frequency may be affected by the temperature or pressure of the system.

How is Larmor precession used in magnetic resonance imaging (MRI)?

In MRI, Larmor precession is used to detect and image the distribution of hydrogen atoms in the body. Hydrogen atoms behave like tiny magnets due to their nuclear spin, and when placed in a strong magnetic field, they precess at a frequency that is specific to the type of tissue they are in. By manipulating the magnetic field and detecting the resulting Larmor precession, MRI machines can produce detailed images of the body's tissues.

Can Larmor precession be observed in everyday life?

Yes, Larmor precession can be observed in everyday life in the form of a spinning top or gyroscope. These objects exhibit precession when spun on a flat surface, as the rotation of the spinning object causes its axis to align with the direction of the Earth's magnetic field, resulting in precession. This effect is the basis for many navigation devices, such as compasses and gyrocompasses.

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