| 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: | Anthony McFadden, University of California at Santa Barbara |
| Authors: | A.P. McFadden, University of California at Santa Barbara T. Brown-Heft, University of California at Santa Barbara N.S. Wilson, University of California at Santa Barbara J.A. Logan, University of California at Santa Barbara C.J. Palmstrøm, University of California at Santa Barbara |
| Correspondent: | Click to Email |
Magnetic tunnel junctions (MTJs) are an increasingly important emerging technology for both magnetic random access memory (MRAM) and spintronics applications. MTJs utilizing CoFeB magnetic electrodes and MgO tunneling barriers have received considerable interest for use in MRAM as desirable properties including perpendicular magnetic anisotropy, high tunneling magnetoresistance ratio, and current induced switching have been demonstrated. While CoFeB/MgO based MTJs have demonstrated remarkable performance, devices utilizing ferromagnetic Heusler compounds have the potential to surpass CoFeB based technologies due to a much higher predicted spin polarization. In addition, many Heusler candidates have even been predicted to be half-metallic (100% spin polarized at the Fermi-level). Of all predicted half-metals, the full-Heusler Co2MnSi has received considerable attention as it is quite stable (ΔHF = -0.441 eV/atom), has a high Curie temperature (Tc=985K), and a large minority-spin energy gap (571 meV). While Heusler based MTJs have the potential to surpass current CoFeB based technology, the spin polarization of Heusler compounds has been shown to be sensitive to atomic ordering, adding an additional challenge to materials growth and integration.
In the present work, the formation of the MgO/Co2MnSi(001) interface has been studied in-situ using X-ray photoelectron spectroscopy (XPS). Co2MnSi layers were grown on Cr-buffered MgO(001) substrates by coevaporation of elemental sources in ultrahigh vacuum while MgO was grown on the Co2MnSi layers using e-beam evaporation of stoichiometric source material. It was found that partial oxidation of the Co2MnSi surface was unavoidable during e-beam evaporation of MgO with oxygen bonding preferentially to Mn and Si. Interestingly, oxidation draws Mn and Si to the surface, resulting in an MgO/Co2MnSi interface with composition significantly different from the unoxidized Co2MnSi surface. In addition, Mn and Si oxides at the MgO/Co2MnSi interface were reduced following annealing in UHV with a corresponding migration of oxygen from the interface into the MgO. The results of XPS studies have been correlated with temperature dependent transport measurements of fully epitaxial CoFe/MgO/Co2MnSi MTJs which were observed to be highly sensitive to post-growth annealing temperature.