Bohr magneton

The Bohr magneton (after Niels Bohr) is the amount of the magnetic moment, which creates an electron with the orbital angular momentum quantum number by its orbital angular momentum. According to the Bohr model of the atom is the ground state, ie the state of lowest energy. The Bohr magneton is used in atomic physics as a unit of magnetic moments.

History

The idea of ​​the elementary magnets is due to Walter Ritz (1907 ) and Pierre -Ernest Weiss. Even before the development of the Atomic Energy rutherford model has been suggested that with the Planck's quantum of action must relate h an elementary magneton. Richard Gans assumed that the ratio of the kinetic energy of the electron to its angular velocity is equal to h, and gave in September 1911 a value that was twice as large as the Bohr magneton. Paul Langevin called in November of the same year at the First Solvay Conference a smaller value for the magneton. The Romanian physicist Ştefan Procopiu found in 1911 using the quantum theory of Max Planck first the exact value of the magneton. Therefore, sometimes the term " drilling Procopiu magneton " heard.

The name " Bohr magneton " received the value only in 1920 by Wolfgang Pauli, of these theoretical value of the magneton with an experimentally determined value ( the so-called white between magneton ) compared in an article.

Magneton generally

In quantum-mechanical consideration of the orbital angular momentum of a charged point particle produces with mass and charge, the magnetic moment

Where the reduced Planck constant and

Called the magneton of the particle.

Magneton of the electron

The magneton of the electron has, according to current measurement accuracy the value:

The bracketed numbers indicate the estimated standard deviation for the mean and refer to the last two digits before the brackets. is the power unit of electron volts, the energy unit and the unit Tesla joules of the magnetic flux density.

Note that due to the negative charge of the electron, its magnetic moment is always directed opposite to its angular momentum. An electron with orbital angular momentum quantum numbers align parallel to the z-axis ( magnetic quantum number ), therefore, the magnetic moment due to this angular momentum ( for example in the p- orbital or on the innermost circular track of the Bohr model of the atom ). The spin angular momentum of electrons contributes to a further magnetic moment of the variable ( opposite to the direction of the spin ).

Has a magnetic ( dipolar ) moment in the magnetic field its lowest energy, if it is contrary to the field, that the orbital angular momentum, and spin is aligned parallel to the field direction.