Investigation of highly ferromagnetic Mn2Ge4 and Mn2Ge5 clusters via photoelectron spectroscopy and theoretical calculations

We investigate the structures and properties of Mn₂Ge₄^-/0 and Mn₂Ge₅^-/0 by anion photoelectron spectroscopy and theoretical calculations. The vertical detachment energies (VDEs) of Mn₂Ge₄^- and Mn₂Ge₅^- are measured to be 2.69 eV and 2.49 eV, respectively. It is found that neutral Mn₂Ge₄ has an approximate quadrilateral bipyramidal structure with C_2v symmetry and ¹¹B₂ electronic state. Neutral Mn₂Ge₅ has a pentagonal bipyramidal structure with C_2v symmetry and ¹¹B₂ electronic state. The 4s-based molecular orbitals of the Mn atoms participate in the chemical bonding with the Ge₄ and Ge₅ fragments in Mn₂Ge₄ and Mn₂Ge₅. In Mn₂Ge₄, the two Mn atoms interact with the Ge₄ moiety via four GeGeMn 3c-2e σ bonds. In Mn₂Ge₅, the two Mn atoms interact with the Ge₅ moiety via one MnGeMn 3c-2e σ bond and four GeMnGe 3c-2e σ bonds. The analysis of magnetic properties reveals that both Mn₂Ge₄ and Mn₂Ge₅ exhibit highly ferromagnetic characteristics with a magnetic moment of 10 μ_B which mainly originated from the Mn atoms. These double Mn atom doped germanium clusters may provide new opportunities to design novel spintronic devices featuring high magnetic moments.