  We investigate spin-dependent conductance across a magnetic tunnel junction
(MTJ) including a ferromagnetic insulating barrier. The MTJ consists of two
half-metallic ferromagnetic La2/3Sr1/3MnO3 (LSMO) manganites as electrodes and
La2NiMnO6 (LNMO) double perovskite as a ferromagnetic insulating barrier. The
resistance of the junction is strongly dependent not only on the orientation of
the magnetic moments in LSMO electrodes, but also on the direction of the
magnetization of the LNMO barrier with respect to that of LSMO. The ratio of
tunnel magnetoresistance reaches a maximum value of 24% at 10 K, and it
decreases with temperature until it completely disappears above the critical
temperature of LNMO at 280 K. The tunneling process is described using a
mechanism which involves both empty and filled eg states of the LNMO barrier
acting as a spin-filter. A magnetic insulating barrier is an interesting path
for achieving room temperature magnetoresistance in oxide-based
heterostructures.
