Structure and magnetic properties of EuNi7+xIn6−x

Samples of compositions EuNi7+xIn6−x (x=0,1,1.3x=0,1,1.3) with the orthorhombic LaNi7In6 type structure were synthesized by heating the elements in sealed tantalum tubes and re-melting in a high-frequency furnace. A single crystal from the EuNi8In5 sample was investigated on the basis of X-ray diffractometer data: Ibam  , a=804.5(2)a=804.5(2), b=916.2(2)b=916.2(2), c=1239.6(3) pmc=1239.6(3) pm, wR2=0.0672wR2=0.0672, 1025 F2F2 values and 40 variable parameters. One 8j position shows a mixed occupancy with 61(1)% In and 39(1)% Ni, leading to the composition EuNi7.79(1)In5.21(1) for the investigated crystal. EuNi7.79In5.21 is only the second representative for the LaNi7In6 type. The structure consists of one-dimensional [Ni7] clusters with NiNi distances ranging from 245 to 274 pm. The cluster units are surrounded by indium atoms and build up an orthorhombic rod packing, where the europium atoms fill cavities between the rods. The magnetic properties strongly depend on composition within the solid solution EuNi7+xIn6−x. While temperature dependent susceptibility measurements of EuNi7In6 and EuNi8In5 samples show for both compounds a Curie–Weiss behaviour indicative for divalent europium and ferromagnetic properties at low temperatures, the ordering temperatures for the two phases are distinctly different being 36 and 2.7 K, respectively. This feature may be related to the degree of atomic disorder in the samples studied. Both indides exhibit metallic conductivity with pronounced anomalies at the respective Curie temperatures.

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