Electron spin

Electrons are negatively charged elementary particles. In addition to their mass and their electrical charge, they have a third important property: the electron spin. The spin (intrinsic angular momentum) of an electron is a quantity in quantum mechanics and describes a classic mechanical angular momentum based on the rotational movement of a mass. The classical electron spin is of fundamental importance for physics and plays a major role in the description of the atomic shell and the macroscopic properties of matter. The electron spin is also directly linked to topics such as magnetism or ferromagnetism.

Why is there an electrospin?

At the beginning of the 20th century, spectroscopic observation of atoms gave rise to a number of ambiguities on how to explain the splitting of the spectral lines (based on the movements of the electrons within an atom). In 1925, the two American physicists Goudsmit and Uhlenbeck proposed assigning the electron a special angular momentum: the electron spin. However, it should be noted that the spin does not indicate the direction of rotation of an electron (as with a gyroscope), but is due to the internal structure of an electron.

The electron spin s (spin quantum number) is specified with two alignment operators: either +1/2 (Up) or -1/2 (Down).

How to measure the electron spin

It has been proven that the electron spin is related to the magnetic moment since it can be used to measure the direction of the electron spin. The Stern-Gerlach experiment proved that silver atoms are deflected in an inhomogeneous magnetic field, so that an electron spin can also be seen here: half of the atoms were deflected in one direction and the other half in the opposite direction.

Taking the Pauli principle into account, the electron spin has a great influence on the movement and location of the particle. In a state of equal energy and identical angular momentum, there can always be exactly two electrons in one atom. The only difference between the two particles is hidden in the oppositely aligned electron spin. They compensate each other, so they are paired.

What are the effects of electron spin?

Certain atoms only contain paired electrons, which means that the entire electron spin goes to zero and does not align itself with an external magnetic field. In this case one speaks of diamagnetism. However, if there is an exchange interaction, the electron spins do not differ in their direction. If this exchange interaction is greater than the thermal energy of the electrons, the material reacts ferromagnetic.