# Bohr magneton

In atomic physics, the Bohr magneton (symbol $\mu _{\mathrm {B} }$ ) is named after the physicist Niels Bohr. It is a physical constant of magnetic moment, defined in SI units by

$\mu _{\mathrm {B} }={{e\hbar } \over {2m_{\mathrm {e} }}}$ and in Gaussian centimeter-gram-second units by

$\mu _{\mathrm {B} }={{e\hbar } \over {2m_{\mathrm {e} }c}}$ where

$e$ is the elementary charge,
$\hbar$ is the reduced Planck's constant,
$m_{e}$ is the electron rest mass
$c$ is the speed of light.

In the SI system of units its value is

$\mu _{\mathrm {B} }$ = 9.274 009 49(80) × 10-24 JT-1.

In the eV system of units its value is

$\mu _{\mathrm {B} }$ = 5.7883 × 10-5 eV•T-1.

In the CGS system of units its value is

$\mu _{\mathrm {B} }$ = 0.927 × 10-20 ErgOe-1 

The Bohr magneton is the natural unit for expressing the electron magnetic dipole moment in the hydrogen atom. It was first calculated by Romanian physicist Stefan Procopiu around 1910 and in some Romanian literature is called the Bohr-Procopiu Magneton. An electron has an intrinsic magnetic dipole moment of approximately one Bohr magneton. 