We studied the double-exchange interaction. The Hamiltonian derived consists of the hoppings of charged fermions and Schwinger bosons. This gives a very simple and clear picture. We also calculated the resistivity with the new Hamiltonian and found that the resistivity is proportional to the square of temperature, if temperature is much lower than the Curie temperature.

• Received 29 April 2002

DOI:https://doi.org/10.1103/PhysRevB.66.132404