Structure, bonding, and magnetic response in two complex borides: Zr2Fe1-delta Ru5+delta B2 and Zr2Fe1-delta(Ru1-xRhx)(5+delta)B-2

Polycrystalline samples of two complex intermetallic borides Zr2Fe1-delta Ru5+delta B2 and Zr2Fe1-delta (Ru1-xRhx)(5+delta)B-2 (delta=ca. 0.10; x=0.20) were synthesized by high-temperature methods and characterized by single-crystal X-ray diffraction, energy dispersive spectroscopy, and magnetization measurements. Both structures are variants of Sc2Fe(Ru1-xRhx)(5)B-2 and crystallize in the space group P4/mbm (no. 127) with the Ti3Co5B2-type structure. These structures contain single-atom, Fe-rich Fe/Ru or Fe/Ru/Rh chains along the c-axis with an interatomic metal-metal distance of 3.078(1) angstrom, a feature which makes them viable for possible low-dimensional temperature-dependent magnetic behavior. Magnetization measurements indicated weak ferrimagnetic ordering with ordering temperatures ca. 230 K for both specimens. Tight-binding electronic structure calculations on a model "Zr2FeRu5B2" using LDA yielded a narrow peak at the Fermi level assigned to Fe-Fe antibonding interactions along the c-axis, a result that indicates an electronic instability toward ferromagnetic coupling along these chains. Spin-polarized calculations of various magnetic models were examined to identify possible magnetic ordering within and between the single-atom, Fe-rich chains. (C) 2010 Elsevier Inc. All rights reserved.