RFe2Mg Al8− (R=La–Nd and Sm; x≈0.8): Flux synthesis, structure, magnetic and electrical properties

Abstract

Single crystals of Mg-substituted CeFe 2 Al 8 type intermetallics RFe 2 Mg x Al 8-x (R = LaNd and Sm; x≤1) were grown by reacting iron and rare earth metals in 1:1 Mg/Al mixed flux. The structure features mono-capped and bi-capped trigonal prismatic FeAl 6 units. Electronic structure calculations indicate that magnesium substitution reduces the valence electron count, shifting the Fermi level away from a pseudo-gap. This changes the electronic nature of the cerium analog; the previously reported ternary CeFe 2 Al 8 shows strong hybridization between the cerium states and the conduction electrons, resulting in no magnetic moment on Ce atoms. On the other hand, magnetic susceptibility measurements on CeFe 2 Mg x Al 8-x indicates a localized moment on cerium. The newly synthesized Pr, Nd and Sm analogs exhibit antiferromagnetic ordering at 2.8 K, 7.8 K and 12 K respectively. Solid state 27 Al NMR of LaFe 2 Mg x Al 8-x exhibits a broad Knight shift at ~1200 ppm, consistent with the metallic behavior shown by electrical resistivity data.

Synthesis, Structure, and Complex Magnetism of MIr2In8 (M = Eu, Sr)

“…11 Instead of the targeted EuIrIn 5 phase or previously reported phases, our synthesis yielded EuIr 2 In 8 , a new compound that crystallizes in the CeFe 2 Al 8 structure type, 12,13 which is also sometimes referred to as the CaCo 2 Al 8 structure type. 14 including the two archetypal members as well as many other aluminides including RFe 2 Al 8 (R = La, Pr, Eu), 15,16 RFe 2 Al 8−x Mg x (R = La, Ce, Pr, Nd, Sm), 17 RCo 2 Al 8 (R = La, Ce, Pr, Sm, Yb), 18−21 25 RCo 2 Ga 8 (R = Ca, Ce, Pr, Yb), 25−27 RRu 2 Ga 8 (R = La, Ce, Pr, Nd), and EuM 2 Ga 8 (M = Rh, Ir), 27 and the indides SrRh 2 In 8 28 and EuRh 2 In 8 . 27 The structure appears to be relatively stable and can be synthetically accessed by a variety of routes including arc melting, direct combination by radiofrequency induction heating, and flux synthesis.…”

“…For example, both CeFe 2 Al 8 and CeCo 2 Al 8 exhibit clear signs of strong electron correlations in both magnetic and transport measurements, 30 and a solid solution of the two with the composition CeCoFeAl 8 exhibits evidence of Ce valence fluctuations. 29 The series RFe 2 Al 8−x Mg x (R = La, Ce, Pr, Nd, Sm) 17 was synthesized in Mg/Al flux, resulting in Mg substitution on the Al sites. All analogues exhibit rather unusual physical properties ranging from evidence for valence fluctuation in the Sm analogue to low-temperature upturns in resistivity for the La and Pr analogues, suggesting the that the Kondo effect plays a role in the behavior of these systems when Mg substitution alters the Fermi level.…”

Chemical Flexibility of Mg in Pnictide Materials: Structure and Properties Diversity

“…Mg can accommodate a wide range of coordination numbers and interatomic distances when covalently bonded to pnictides, resulting in diverse crystal chemistry. The revealed structural trends are not unique for pnictides but also for other classes of compounds, such as aluminides, silicides, and germanides. − From a chemical bonding standpoint, Mg is often engaged in two-center covalent interactions, as in Mg 3 Sb 2 . Multicenter bonding can be achieved in the high-pressure phases, such as recently reported multicenter Mg–Si interactions in MgSi 5 .…”