| AVS 64th International Symposium & Exhibition | |
| Electronic Materials and Photonics Division | Monday Sessions |
| Session EM+MI+TF-MoM |
| Session: | Growth, Electronic, and Magnetic Properties of Heusler Compounds |
| Presenter: | Tobias Brown-Heft, University of California at Santa Barbara |
| Authors: | T. Brown-Heft, University of California at Santa Barbara A.P. McFadden, University of California at Santa Barbara J.A. Logan, University of California at Santa Barbara C. Guillemard, University of Lorraine, France P. Le Fevre, Synchrotron SOLEIL, France F. Bertran, Synchrotron SOLEIL, France S. Andrieu, University of Lorraine, France C.J. Palmstrøm, University of California at Santa Barbara |
| Correspondent: | Click to Email |
Ferromagnetic contacts are used as a source of spin-polarized current in many spintronic devices. Desired properties for ferromagnetic contacts used in magnetic tunnel junctions and other next-generation memory elements are perpendicular magnetic anisotropy and 100% spin polarization at the Fermi level (half-metallicity). Heusler compounds are strong candidates for this purpose as many have been predicted and observed to be half-metals (e.g. Co2MnSi), while others exhibit perpendicular magnetic anisotropy (e.g. Co2FeAl/MgO(001)). However, until now both properties have not been observed by experiment in a single material. J. Azadani et al have predicted that perpendicular anisotropy can be combined with half-metallicity by growing atomic-period superlattices of two different Heusler compounds [1]. We have successfully grown a single-crystal superlattice formed by layers of Co2MnAl and Fe2MnAl with periodicity of one to three unit cells using molecular beam epitaxy. X-ray diffraction reciprocal space mapping reveals that the superlattice is compliant to the substrate to at least 20 nm film thickness, sustaining strains from -3.0% (tensile) on MgO(001) to +2.3% (compressive) on GaAs(001). The film strain is accommodated via tetragonal distortion of c/a = 0 .96 to 1.06, respectively. The tetragonal distortion on GaAs(001) contributes to perpendicular magnetic anisotropy, resulting in films exhibiting out-of-plane magnetic easy axes at temperatures below 200K. Films with aluminum content higher than nominal stoichiometry may also help to induce perpendicular magnetization by reducing saturation magnetization, thereby lowering thin-film shape anisotropy. Superlattice structure was verified using electron energy loss spectroscopy in TEM, which shows low interface diffusion of cobalt and iron and high elemental contrast between individual superlattice layers. S pin polarization of >90% near the Fermi level has been measured directly via spin-resolved photoemission spectroscopy. Spin-resolved photoemission spectra suggest that the termination layer near a tunnel barrier interface should be Co2MnAl-like, and may benefit from further composition tuning. This work was supported in part by C-SPIN, one of the six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA. We also acknowledge support from the Vannevar Bush Faculty Fellowship.
[1] J. G. Azadani et al. J. Appl. Phys. 119, 043904 (2016).