Tetragonal Heusler Compounds for Spintronics

With respect to the requirements of spin torque transfer (STT) materials, one the most promising materials families are the tunable tetragonal Heusler compounds based on Mn
₂
YZ
(
Y
=Co,Fe,Ni,Rh,...;
Z
=Al, Ga, Sn). They form the inverse cubic Heusler structure with three distinct magnetic sublattices, which allows a fine tuning of the magnetic properties. Starting with the stoichiometric Mn
₃
Ga compound, we explored the complete phase diagram of Mn
_3-x
Y
_x
Z
(
Y
=Co, Fe, Ni and
Z
=Ga ). All series exhibit thermally stable magnetic properties. As we demonstrate, Mn
_3-x
Fe
_x
Ga series, which are tetragonal over the whole range of compositions, are good as hard magnets, whereas magnetically more weak Mn
_3-x
Ni
_x
Ga series exhibit the shape memory phenomenon. Even more surprising properties are found in the Co-based series. On the one hand, the Co-poor (x <; 0.5) Mn
_3-x
Co
_x
Ga tetragonal alloys are well-suited for the STT. At the same time, the Co-rich cubic series (0.5 <; x <; 1) are half-metallic ferromagnets, following the Slater-Pauling rule, similar to Co
₂
YZ
cubic Heusler compounds.