Magnetoresistance of ferromagnetic tunnel junctions in the double-exchangemodel

We conduct a theoretical study of the temperature dependence of the spin po larization (P) and the magnetoresistance (MR) ratio using the double exchan ge (DE) model for ferromagnetic tunnel junctions with half-metallic systems . It is shown that the strong exchange coupling in the DE model plays an im portant role in the temperature dependence of both P and the MR ratio; thei r values can be less than the maximum values expected for half-metallic sys tems at low temperatures, and the MR ratio decreases more rapidly than P wi th increasing temperature. The calculated results, however, indicate that t he MR ratio may still be large at high temperatures near the Curie temperat ure.