title: Ternary borides Nb7Fe3B8 and Ta7Fe3B8 with Kagome-type iron framework.
abstract: Two new ternary borides TM7Fe3B8 (TM = Nb, Ta) were synthesized by high-temperature thermal treatment of samples obtained by arc-melting. This new type of structure with space group P6/mmm, comprises TM slabs containing isolated planar hexagonal [B6] rings and iron centered TM columns in a Kagome type of arrangement. Chemical bonding analysis in Nb7Fe3B8 by means of the electron localizability approach reveals two-center interactions forming the Kagome net of Fe and embedded B, while weaker multicenter bonding present between this net and Nb atoms. Magnetic susceptibility measurements reveal antiferromagnetic order below TN = 240 K for Nb7Fe3B8 and TN = 265 K for Ta7Fe3B8. Small remnant magnetization below 0.01μB per f.u. is observed in the antiferromagnetic state. The bulk nature of the magnetic transistions was confirmed by the hyperfine splitting of the Mössbauer spectra, the sizable anomalies in the specific heat capacity, and the kinks in the resistivity curves. The high-field paramagnetic susceptibilities fitted by the Curie-Weiss law show effective paramagnetic moments μeff≈ 3.1μB/Fe in both compounds. The temperature dependence of the electrical resistivity also reveals metallic character of both compounds. Density functional calculations corroborate the metallic behaviour of both compounds and demonstrate the formation of a sizable local magnetic moment on the Fe-sites. They indicate the presence of both antiferro- and ferrromagnetic interactions.
authors.affiliation: Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, 01187 Dresden, Germany. zheng@cpfs.mpg.de qiangzhengsic@gmail.com.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zheng
authors.forename: Roman
authors.initials: R
authors.lastname: Gumeniuk
authors.forename: Horst
authors.initials: H
authors.lastname: Borrmann
authors.forename: Walter
authors.initials: W
authors.lastname: Schnelle
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Tsirlin
authors.forename: Helge
authors.initials: H
authors.lastname: Rosner
authors.forename: Ulrich
authors.initials: U
authors.lastname: Burkhardt
authors.forename: Michael
authors.initials: M
authors.lastname: Reissner
authors.forename: Yuri
authors.initials: Y
authors.lastname: Grin
authors.forename: Andreas
authors.initials: A
authors.lastname: Leithe-Jasper