Synthesis, crystal structure, and magnetism of A2Co12As7 (A=Ca, Y, Ce–Yb)

Abstract

Ternary intermetallics, A2Co12As7 (A = Ca, Y, Ce-Yb), have been synthesized by annealing mixtures of elements in molten Bi at 1223 K. The materials obtained crystallize in the P63/m variant of the Zr2Fe12P7 structure type. The unit cell volume shows a monotonic decrease with the increasing atomic number of the rare-earth metal, with the exception of Ce-, Eu-, and Yb-containing compounds. An examination of these outliers with X-ray absorption near edge structures (XANES) spectroscopy revealed mixed valence of Ce, Eu, and Yb, with the average oxidation states of +3.20(1), +2.47(5), and +2.91(1), respectively, at room temperature. Magnetic behavior of A2Co12As7 is generally characterized by ferromagnetic ordering of Co 3d moments at 100-140 K, followed by low-temperature ordering of rare-earth 4f moments. The 3d-4f magnetic coupling changes from antiferromagnetic for A = Pr-Sm to ferromagnetic for A = Ce and Eu-Yb. Polarized neutron scattering experiments were performed to support the postulated ferro-and ferrimagnetic ground states for Ce2Co12As7 and Nd2Co12As7, respectively.Reactions in molten metal fluxes remain somewhat underused in the syntheses of R-T intermetallics, which are dominated by arc-melting and direct annealing techniques. Nevertheless, the use of various molten metals as reaction media has been steadily expanding, with the increased understanding that this method not only offers access to new materials, but also affords lower reaction temperatures and highquality single crystals for physical property measurements [9].

Driving the Europium Valence State in EuCo2As2 by External and Internal Impact

“…We can also note that the maximum europium valence reached in our experiment in the sample with x = 0.5 at the pressure of 38.8 GPa is +2.65, while the isostructural and closely related compound EuCo 2 P 2 undergoes the transition to an almost trivalent state at much smaller pressure [4,[7][8][9][10][11]13]. This again confirms the softness of EuCo 2 As 2 lattice, but also agrees with the more electronegative nature of the phosphorus atoms, which causes phosphides to favor higher oxidation states of Eu as compared to arsenides [14]. The larger As ion increases the lattice parameter c and the distance between different atomic layers in the structure in comparison with EuCo 2 P 2 .…”

Crystal structure of the new ternary arsenide Y8Co41As25

“…Потрійні системи Ln-Co-As вивчено значно меншою мірою, зокрема, у системі Y-Co-As відомо про існування лише двох тернарних арсенідів сталого складу Y 2 Co 12 As 7 [11][12][13] та YCo 5 As 3 [14,15], які є представниками рядів ізоструктурних сполук Ln 2 Co 12 As 7 (структурний тип Zr 2 Fe 12 P 7 [16] або похідний від нього тип структури Ba 7 Cl 2 F 12 для Ln = Y, Ce-Lu) та LnCo 5 As 3 (структурний тип YCo 5 Р 3 [17], Ln = Y, Gd-Er). У працях [13,14] виконано повне дослідження кристалічної структури арсенідів, відповідно, Ln 2 Co 12 As 7 (Ln = Y, Ce-Lu) та YCo 5 As 3 рентгеноструктурним методом монокристала і полікристала; у праці [15] методом монокристала визначено координати та параметри теплового зміщення атомів у структурах арсенідів TbCo 5 As 3 та ErCo 5 As 3 , а методом полікристала повністю вивчено структуру сполук LnCo 5 As 3 , де Ln = Gd, Dy, Ho, і підтверджено належність їхньої кристалічної структури до типу YCo 5 P 3 .…”