In physics, Larmor precession (also "Lamour") refers to the precession of the magnetic moments of electrons or atomic nuclei in atoms around the direction of an external magnetic field. The magnetic field exerts a torque on the magnetic moment, producing a gyroscopic motion, much like the spinning of a top. The angular velocity of the precession is

$\backslash omega\_\{0\}\; =\; -\backslash gamma\; \backslash textbf\{H\}\_0$,

where $\backslash gamma$ is the gyromagnetic ratio and $\backslash textbf\{H\}\_0$ is the external magnetic field. The gyromagnetic ratio is different for each type of atomic nucleus, but is typically given by

$\backslash gamma\; =\; \backslash frac\{g\backslash mu\_\{B\}\}\{\backslash hbar\}$,

where $g$ is the Lande g-factor, $\backslash mu\_\{B\}$ is the Bohr magneton, and $\backslash hbar$ is Dirac's constant. For an electron, the gyromagnetic ratio is approximately 17.61 Mhz / Oe.

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 by J. H. E. Griffiths in 1946.

The concept of Larmor precession is used in nuclear magnetic resonance.

See also

• Rabi cycle

Precession | Electromagnetism | Atomic physics

Precessione di Larmor | 拉莫頻率