Berlin 2005 – scientific programme

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MA: Magnetismus

MA 18: Magnetische dünne Schichten III

MA 18.4: Talk

Monday, March 7, 2005, 11:15–11:30, TU H1028

First-principles study of thin magnetic transition-metal alloy films on Si(001) — •Hua Wu, Peter Kratzer, and Matthias Scheffler — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4–6, D-14195 Berlin

Ferromagnetic (FM) metal/semiconductor heterojunctions have promising technological applications in the field of magnetoelectronics (or spintronics). Here we present density-functional theory calculations addressing the thermodynamic stability and magnetism both of the pseudomorphic CsCl-like MSi (M=Mn,Fe,Co,Ni) thin films and of the Heusler alloy M₂MnSi (M=Fe,Co,Ni) films on Si(001). The results show that the MSi films prefer a Si-termination, and that the M-Si bond-strength increases as M varies from Mn to the later transition metals, which is helpful to understand a number of experimental observations. The ultrathin MnSi film is FM; the FeSi and NiSi films are nonmagnetic; while the CoSi film is surprisingly FM due to its peculiar electronic band structure. For the M₂MnSi films, the Si termination has a higher chemical stability due to stronger surface chemical bonds, while the MnSi termination has a higher thermodynamic stability due to a lower formation energy. The calculated strength of the effective intralayer Mn-Mn coupling scales with the measured FM Curie temperatures of the bulk M₂MnSi. In particular, the Co₂MnSi/Si(001) thin film is stable against a phase separation and has a robust FM ground state as in the bulk Co₂MnSi. However, we note that in the Co₂MnSi/Si(001) film, the formation energies of Co/Si and MnSi/Si interfaces are similar, which could lead to interfacial disorder degrading spin injection.