larmor frequency

Larmor precession

[lahr-mawr]
In physics, Larmor precession (named after Joseph Larmor) refers to the precession of the magnetic moments of electrons, atomic nuclei, and atoms about an external magnetic field. The magnetic field exerts a torque on the magnetic moment,
vec{Gamma} =
vec{mu}timesvec{B}= gammavec{J}timesvec{B}

where vec{Gamma} is the torque, vec{J} is the angular momentum vector, vec{B} is the external magnetic field, times is the cross product, and gamma is the gyromagnetic ratio which gives the proportionality constant between the magnetic moment and the angular momentum. The angular momentum vector vec{J} precesses about the external field axis with an angular frequency known as the Larmor frequency,

omega = gamma B
where omega is the angular frequency and B is the magnitude of the magnetic field.

A famous 1935 paper published by Lev Landau and Evgeny Lifshitz predicted the existence of ferromagnetic resonance of the Larmor precession, which was verified experimentally and independently by J. H. E. Griffiths (UK) and E. K. Zavoiskij (USSR) in 1946.

Larmor precession is important in nuclear magnetic resonance.

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