Z (Z=Ge, Sn, Sb) Heusler films prepared by chemical templating

The task of improving the performances of next-generation spin-transfer torque magnetoresistive random access memory (STT-MRAM) requires the use of new magnetic materials with high perpendicular magnetic anisotropy (PMA) and low magnetic moment within the magnetic tunnel junction, i.e. MRAM storage element. Heusler alloys are a large family of compounds with tunable magnetic properties. Some of these have a tetragonal structure with its elongated axis perpendicular to the film plane and thus they may display PMA due to their structure broken symmetry. However, so far, PMA has been observed only for 50Å-thick films, i.e. too thick for technological applications. In this talk we demonstrate that X₃Z (X=Mn; Z=Ge,Sn,Sb) tetragonal Heusler films, as thin as only 1 unit cell, can be developed by using a novel chemical templating technique. We show this can be achieved by growing the Heusler films, even at room temperature, onto atomically-ordered X’Z’ (X’=Co; Z’=Al,Ga,Ge,Sn) underlayers that promote chemical ordering within the Heusler films. Excellent PMA with square hysteresis is found in Mn₃Z layers that are only 1-2 unit cells thick. The possibility of preparing ultrathin Heusler films with PMA makes possible their technological application for a wide range of spintronic devices.