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MA: Magnetismus
MA 17: Magnetic Materials II
MA 17.2: Vortrag
Dienstag, 28. März 2006, 10:30–10:45, HSZ 401
Complex magnetic order and transition to half-metallicity in Mn-doped Fe3Si — •Phivos Mavropoulos, Marjana Ležaić, and Stefan Blügel — IFF, Forschungszentrum Jülich, D-52425 Jülich, Germany
Fe3Si is a ferromagnetic material with possible applications in magnetic tunnel junctions [1]. When doped with Mn, the material shows a complex magnetic behavior, as suggested by older experiments [2]. Motivated by the above, we employed the Korringa-Kohn-Rostoker Green function method within density-functional theory in order to study the alloy Fe3−xMnxSi, with 0≤ x≤ 1. The Mn atoms are positioned at the octahedral site of the L21 crystal structure. Chemical disorder is described within the coherent potential approximation (CPA); magnetic disorder is considered within the disordered local moment (DLM) state, again using the CPA. We find that, for x≤ 0.3, the Mn atoms align antiferomagnetically (Mn↓) to the Fe atoms, while for x≥ 0.75 the alignment is ferromagnetic (Mn↑). For intermediate Mn concentrations, the energy minimum is at a DLM state of the form Fe3−x(Mnx−y↓Mny↑)Si, in which only a fraction y of the Mn atoms is ferromagnetically coupled to Fe. In the concentrated limit (x=1), the (ordered) alloy is half-metallic. For lower concentrations the spin polarization at the Fermi level is also considerable: for x=0.65, P=0.93, and for x=0.55, P=0.85.
We discuss the origin of the transition to ferromagnetic behavior, the exchange interactions and the spin polarization.
[1] A. Ionescu et al., Phys. Rev. B 71, 094401 (2005)
[2] S. Yoon and J. G. Booth, J. Phys. F: Met. Phys. 7, 1079 (1977)