Ternäre und quaternäre Eisennitride mit Spinglasverhalten

The present work identifies the first canonical spin glasses of ternary iron nitrides MxFe4-xN (0 < x < 1), that are derived from ferromagnetic gamma'-Fe4N by substituting iron atoms with elements of the III. and IV. main group. For M = Sn, Ge, Ga, Al, Si the structural and magnetic properties are studied with experimental and quantum-chemicalmethods. Furthermore, the solid solution SnxGe1-xFe3N is characterized as a quaternary nitride. Combined DC and AC magnetometry reveal the M-rich nitrides Sn0.9Fe3.1N, Ge0.97Fe3.03N0.56 und Ga0.9Fe3.1N as spin glasses with RKKY indirect-exchange interactions. Within their solid solutions, the gradual incorporation of M is accompanied by a drastic weakening of the ferromagnetic interactions, which can be explained in SnxFe4-xN by the Stoner criterion on the basis of electronic structure calculations and a quantum-theoretical bonding analysis. Competing ferromagnetic and antiferromagnetic exchange interactions cause the long-ranged frustration of iron spins, and the spin dynamic below the spin glass transition temperature is characterized by a broad andasymmetrical distribution of relaxation times. This study concentrates on metastable nitrides SnxFe4-xN (0 <= x <= 0.9), for which a modified two-step ammonolytic synthesis with a very small nitridation temperature corridor is presented. Structure, composition and properties are comprehensively described by X-ray and neutron scattering, thermal analyses, REM/EDX and a PGAA analysis in synergy with DFT calculations. The substitution expands the unit cell of the antiperovskite structure (space group Pm-3m) with a Vegard-type behavior of the lattice parameter over the compositional range, with an exception for a small internal miscibility gap of unknown cause around Sn0.33Fe3.67N (0.25 < x < 0.37). Next, the lighter homologous nitride GexFe4-xNy (0 <= x <= 0.97) is addressed, where the germanium-richest composition, Ge0.97Fe3.03N0.56, features a tetragonally distorted structure (space group I4/mcm) with a more favorable total energy and chemical bonding. At high temperature, a phase transition to the cubic modification is evidenced. Moreover, GexFe4-xNy has a limited nitrogen capacity, that may be due to dynamic instabilities inthe crystal structure. The exact composition MFe3N is not accessible as a bulk material. However, it can be realized as a thin film GaFe3N, for which no frustrated behavior was observed. This reveals the importance of a few, statistically distributed iron atoms on the non-magnetic metal position for the spin glass behavior in MxFe4-xN. Furthermore, the structural and magnetic properties of the solid solutions AlxFe4-xN and SixFe4-xN, that have not been synthesized yet, are predicted by DFT calculations, and a frustrated spin system is proposed for aluminum- and silicon-rich iron nitrides. Finally, the quaternary nitride SnxGe1-xFe3N (0 <= x <= 0.9) shows spin glass behavior, and the spin glass transition temperature depends on the composition