  The temperature and voltage dependence of spin transport is theoretically
investigated in a new type of magnetic tunnel junction, which consists of two
ferromagnetic outer electrodes separated by a ferromagnetic barrier and a
nonmagnetic (NM) metallic spacer. The effect of spin fluctuation in magnetic
barrier, which plays an important role at finite temperature, is included by
taking the mean-field approximation. It is found that, the tunnel
magnetoresistance (TMR) and the electron-spin polarization depend strongly on
the temperature and the applied voltage. The TMR and spin polarization at
different temperatures show an oscillatory behavior as a function of the NM
spacer thickness. Also, the amplitude of these oscillations is regularly
reduced when the temperature increases. The maximum TMR value, varies
approximately from 270% in reverse bias (at $T$=0 K) to 25% in forward bias (at
$T\geq T_C$).
