Self-assembled nano- to micron-size fibers from molten R11Ni4In9 intermetallics

Abstract

A study of the formation of Gd11M4In9 (M=Ni, Pd, Pt) and R11Ni4In9 (R=rare earth) compounds revealed a unique and peculiar property, which is to naturally crystallize in a bundle of self-assembled fibers when cooled from the melt. The fibers, which are nano- to millimeters in cross-section and ≈1–40mm long, grow unidirectionally along a temperature gradient. These compounds adopt the orthorhombic Nd11Pd4In9 structure type (oC48-Cmmm). This structure is layered, with slabs of R atoms alternating with slabs of Ni/In atoms along a short c-axis (much shorter than either the a- or b-axis). The growth direction of the fibers is along the crystallographic c-axis, orthogonal to the a–b plane. Two strong and short In–In bonds lie in the a–b plane, which are even shorter than in In metal. Integrated crystal orbital Hamilton population calculations show that the In–In bonds create isolated “R8Ni4In9” rods growing along the c-axis, with the In–In bonds being part of the rods. This appears to be an important factor explaining the microfibrous nature of these phases. Some physical properties have been measured on the Gd11Ni4In9 homolog. The compound orders ferrimagnetically at TC≈88K, and at lower temperatures (46 and 10K), two other magnetic anomalies were observed, probably due to spin reorientations. As expected from the bonding features, the mechanical, magnetic and electrical properties are strongly anisotropic.