The double-exchange mechanism is a type of a magnetic exchange that may arise between ions in different oxidation state

Oxidation state

In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...

. First proposed by Clarence Zener

Clarence Zener

Clarence Melvin Zener was the American physicist who first described the property concerning the breakdown of electrical insulators. These findings were later exploited by Bell Labs in the development of the Zener diode, which was duly named after him...

, this theory that predicts the relative ease with which an electron

Electron

The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

 may be exchanged between two species, and has important implications for whether materials are ferromagnetic, antiferromagnetic, or neither. For example, consider the 180 degree interaction of Mn

Manganese

Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

-O

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

-Mn in which the Mn "e_g" orbitals are directly interacting with the O "2p" orbitals, and one of the Mn ions has more electrons than the other.