Task 2: Heusler alloys with large perpendicular anisotropy

2.1-A Fabrication and characterization of half-metallic Heusler alloy films with large perpendicular magnetic anisotropy (Mizukami, Miyazaki – Sendai)

Tunnel magnetoresistance (TMR) and spin transfer effect opened up possibilities of novel "active" spintronics devices, such as an electrically switchable magnetic tunnel junction for memory application and an electrically tuneable nano-scaled microwave oscillator for rf-application. The device performance depends not only on TMR ratio and critical current density for spin transfer but also on magnetic anisotropy of electrode material which determines thermal stability as well as oscillation frequency. Thus, it is of quite importance to realize new materials which have low saturation magnetization, low magnetic damping, high spin polarization, and high magnetic anisotropy. Candidates are in the class of half-metallic Heusler alloy with large magnetic anisotropy. The goal of this project is the search for such Heusler alloys, the growth of its high-quality films, and the characterization experimentally to understand the underlying physics in this new class of materials.

2.2-A Half-metallic Heusler alloys combined with L10 ordered alloy films (Sakuraba, Takanashi – Sendai)

The materials having large uniaxial magnetic anisotropy such as L10-ordered alloys and RE-TM alloys are extensively studied in the spintronics research field in recent years, because they show a high thermal stability even on the nanometer scale, and they can also be utilized as a perpendicular spin injector into non-magnetic metals/semiconductors. Generally, however, these materials do not have high spin-polarization at the Fermi level. Therefore, it is difficult to extract a highly spin-polarized current from these materials. The central goals of this project are (i) to fabricate half-metallic Heusler alloy films with large perpendicular magnetic anisotropy by combining them with L10-ordered alloys, and (ii) investigate spin-transport properties using them as a spin injector.

2.3-A New compounds with large perpendicular magnetic anisotropy and for spin-torque application (Felser – Mainz)

Goal of this project is the design of new tetragonal half-metallic compounds for spin torque application. Heusler compounds can be designed as low-damping materials, with damping values smaller than for conventional ferromagnetic metals such as CoFe. It is well established that the Co₂YZ Heusler compounds are the only theoretical half metallic compounds for which high spin polarisation was realized in tunnel junctions. A reduced saturation magnetization despite a high Curie temperature can be found for ferrimagnetic Heusler compounds such as CoMn₂Z and related compounds such as Mn₃Ga. However, tetragonal Heusler compounds are of special interest due to their large perpendicular magnetic anisotropy. Especially Heusler compounds with Gallium and Tin show the structural instabilities. Several possible ferro- and ferrimagnetic candidates with tetragonal distortion will be synthesized and investigated within the project such as Mn₂FeZ, CoMn₂Z, XCr₂Z, and XMn₂Z.