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Ladders of a Magnetically Active Element in the Structure of the Novel Complex Boride Ti9Fe2Ru18B8: Synthesis, Structure, Bonding, and Magnetism

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posted on 17.03.2008, 00:00 by Boniface P. T. Fokwa, German D. Samolyuk, Gordon J. Miller, Richard Dronskowski
Polycrystalline samples and single crystals of the complex boride Ti9Fe2Ru18B8 were synthesized by arc-melting the elements and characterized by single-crystal X-ray diffraction and energy-dispersive X-ray analysis. Ti9Fe2Ru18B8 is a new substitutional variant of the Zn11Rh18B8 structure type, space group P4/mbm (No. 127), whose remarkable feature is that it contains one-dimensional chains of dumbbells of magnetically active Fe atoms, which form “ladders” along the c axis. The Fe−Fe distance within a dumbbell is 2.489(2) Å, and the Fe2−Fe2 distance between two dumbbells is 2.968(1) Å; in contrast, the chains are well-separated from each other by distances of at least 11.217(2) Å. According to the results of tight-binding electronic structure calculations, Ru−B and Ti−Ru contacts are responsible for the structural robustness, while Fe−Fe interactions influence the magnetic behavior. According to magnetization measurements, Ti9Fe2Ru18B8 orders ferromagnetically between 10 and ~200 K. A model for ferromagnetism in this ladder-based structure identifies ferromagnetic coupling among neighboring spin-triplet Fe2 dimers along the c axis as the origin of the magnetic behavior.