  We propose a theoretical model for an all-Heusler magnetic tunnel junction
that uses two Heusler compounds: Fe$_2$CrSi and Fe$_2$TiSi, both of which can
be experimentally synthesized. Fe$_2$CrSi is a half-metallic ferromagnet,
making it a promising material for efficient spin injection in magnetic random
access memories and other spin-dependent devices. While, Fe$_2$TiSi is a
nonmagnetic semiconductor that has the same lattice structure and comparable
lattice constant with Fe$_2$CrSi, as it can be obtained by substituting the
$Y$-site atoms in Fe$_2$CrSi. By using Fe$_2$TiSi as a tunneling barrier
sandwiched by two pieces of semi-infinite Fe$_2$CrSi to construct an
all-Heusler magnetic tunnel junction, the interface disorder is naturally
reduced. Our calculations demonstrate that this magnetic tunnel junction can
exhibit a giant tunneling magnetoresistance of up to 10$^{9}$\% and remains
robust under finite bias voltage. These characteristics suggest that
Fe$_2$CrSi/Fe$_2$TiSi/Fe$_2$CrSi MTJ will be an ideal candidate for future
spintronic applications. More importantly, such a device model can keep such a
giant tunneling magnetoresistance at and beyond room temperature due to the
high Curie temperature of Fe$_2$CrSi.

Applied Physics