Scaffolding, Ladders, Chains, and Rare Ferrimagnetism in Intermetallic Borides: Synthesis, Crystal Chemistry and Magnetism

Abstract

Single-phase polycrystalline samples and single crystals of the complex boride phases Ti 8 Fe 3 Ru 18 B 8 and Ti 7 Fe 4 Ru 18 B 8 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 Zn 11 Rh 18 B 8 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, ABSTRACT:Single-phase polycrystalline samples and single crystals of the complex boride phases Ti 8 Fe 3 Ru 18 B 8 and Ti 7 Fe 4 Ru 18 B 8 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 Zn 11 Rh 18 B 8 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 chainÀladderÀchain, 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, Ti 8 Fe 3 Ru 18 B 8 and Ti 7 Fe 4 Ru 18 B 8 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 Ti 8 Fe 3 Ru 18 B 8 is unexpectedly smaller than the recently reported Ti 9 Fe 2 Ru 18 B 8 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 H c value (28.6 kA/m), measured for Ti 7 Fe 4 Ru 18 B 8 , lies just at the border of those of hard magnetic materials.

Scaffolding, Ladders, Chains, and Rare Ferrimagnetism in Intermetallic Borides: Electronic Structure Calculations and Magnetic Ordering

“…n = 2, which is in good agreement with experiment. 8 Another factor influencing the observed range of VE counts in Ti 9-n Fe 2þn Ru 18 B 8 includes states associated with the Fe1-ladders and the 3d metal 2b-chains. The ligand field splitting of these Fe atomic orbitals was determined through a 'fatband' analysis of the bands between À1.5 and 1.5 eV, the results of which are illustrated in Figure 5.…”

“…8 The total DOS curves reveal a pseudogap at the corresponding Fermi levels, while invoking spin polarization results in the formation of large, localized magnetic moments at the Fe atoms and some polarization induced at the neighboring Ru atoms. An analysis of ÀCOHP curves shows a bonding network similar to those described in Ti 9 Fe 2 Ru 18 B 8 and Ti 9 M 2 Ru 18 B 8 (M = Cr, Mn, Co, Ni, Cu, Zn).…”

“…With greater Fe content, e.g., as in "Ti 7 Fe 4 Ru 18 B 8 ", the measured magnetic moment should increase because substitution at the 4h-chain site will lead to a considerable increase in Fe content, an enhanced local moment from substitution at the 4h-chain, and the amplified magnetic moment in the 'ladder'. In fact, preliminary experimental data show the measured magnetic moment in Ti 8 Journal of the American Chemical Society ARTICLE of magnetically ordered models in Ti 9-n Fe 2þn Ru 18 B 8 must be established. First, we will investigate possible magnetic structures through an analysis of the magnetic and nonmagnetic ÀCOHP curves using the "Ti 6 Fe 5 Ru 18 B 8 " (n = 3) model in which the 2b-and 4h-chain sites contain Fe atoms.…”

“…Further addition of iron to this species, by replacing Ti according to Ti 9-n Fe 2þn Ru 18 B 8 (n = 1, 2), has been synthesized and shows Fe-based 'ladders' as well as additional 'chains', about which the reader is referred to ref 8. These 'chains' are similar to those present in the isostructural Zn 10 FeRh 18 B 8 and the analogous Sc 2 Fe(Ru 5-x Rh x )B 2 (x = 0À5) and Zr 2 Fe 1Àδ (Ru 1-x Rh x ) 5þδ B 2 (δ = ca.…”

Thermal conductivity of PrRh4.8B2, a layered boride compound

“…[1][2][3][4][5][6][7] Regarding properties, many studies have been carried out into the magnetism of borides, [7][8][9][10][11][12][13][14] and recent especial efforts have been made to develop the high temperature thermoelectric properties of novel borides. [15][16][17][18][19][20] Being refractory materials, thermoelectric borides have the potential to be used in high impact energy-saving applications like topping cycles for power plants and waste heat power generation in industry.…”