Double exchange couples localized magnetic moments through actual carrier hopping between sites of different valence. Strong local Hund's coupling makes hopping energetically easier when neighboring core spins align, lowering the carrier kinetic energy. In the classical strong-coupling limit, a common effective hopping is for relative spin angle ; aligned cores maximize its magnitude. Unlike insulating superexchange, this mechanism directly connects carrier motion and magnetic alignment.[ref]
Interaction between the d-Shells in the Transition Metals. II. Ferromagnetic Compounds of Manganese with Perovskite Structure by Clarence Zener. 1951 abstract: the observed connection between conduction and ferromagnetism in manganese perovskites motivates the double-exchange mechanism
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The double-exchange mechanism is a concept in solid-state physics and materials science that explains the behavior of electrons in certain types of materials, particularly in relation to ferromagnetism and electron transport. It describes how the movement of one type of electron can be coupled with the spin state of another electron, leading to unique magnetic and electrical properties.