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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. [ABSTRACT FROM AUTHOR]

Single-phase polycrystalline samples and single crystals of the complex boride phases Ti8Fe3Ru18B8 and Ti7Fe4Ru18B8 have been synthesized by arc melting the elements. The phases were characterized by powder and single-crystal X-ray diffraction as well as energy-dispersive X-ray analysis. They are new substitutional variants of the Zn11Rh18B8 structure type, space group P4/mbm (no. 127). The particularity of their crystal structure lies in the simultaneous presence of dumbbells which form ladders of magnetically active iron atoms along the [001] direction and two additional mixed iron/titanium chains occupying Wyckoff sites 4h and 2b. The ladder substructure is ca. 3.0 Å from the two chains at the 4h, which creates the sequence chain-ladder-chain, establishing a new structural and magnetic motif, the scaffold. The other chain (at 2b) is separated by at least 6.5 Å from this scaffold. According to magnetization measurements, Ti8Fe3Ru18B8 and Ti7Fe4Ru18B8 order ferrimagnetically below 210 and 220 K, respectively, with the latter having much higher magnetic moments than the former. However, the magnetic moment observed for Ti8Fe3Ru18B8 is unexpectedly smaller than the recently reported Ti9Fe2Ru18B8 ferromagnet. The variation of the magnetic moments observed in these new phases can be adequately understood by assuming a ferrimagnetic ordering involving the three different iron sites. Furthermore, the recorded hysteresis loops indicate a semihard magnetic behavior for the two phases. The highest Hc value (28.6 kA/m), measured for Ti7Fe4Ru18B8, lies just at the border of those of hard magnetic materials. [ABSTRACT FROM AUTHOR]