An electron in a ferromagnetic crystal (the magnetic polaron)

The properties of a conduction electron in a ferromagnetic crystal (magnetic polaron) have been investigated. The magnetic spins are treated within the idealized boson representation. At absolute zero a large number of terms in the perturbation expansion are zero and the remainder can be summed exactly. For strong coupling it is demonstrated that, for certain total spin states, slight narrowing of the conduction electron bandwidth can occur. This narrowing depends on the magnitude of the atomic spin in the form of a factor 2s/2s+1.