The nano-microfibrous R11Ni4In9 intermetallics: New compounds and extraordinary anisotropy in Tb11Ni4In9 and Dy11Ni4In9

Abstract

R11Ni4In9 (R=rare earth) compounds exhibit an unusual self-assembled nano/microfibrous morphology that results in anisotropic structural and magnetic behaviors. The existence of new compounds for R=Dy, Ho, Er, Tm and Lu, has been established (orthorhombic Nd11Pd4In9-type, oC48, Cmmm, Z=2), showing that the formation of these phases, previously known for R=La–Nd, Sm, Gd, Tb and Y, extends to all of the rare earth elements, except Sc, Eu and Yb. The results of physical property measurements performed on oriented fibers of Tb11Ni4In9, Dy11Ni4In9 and Y11Ni4In9 are presented. Multiple magnetic transitions are observed in Tb11Ni4In9 and Dy11Ni4In9 with the highest ordering temperature, TC, of 112 and 88K, respectively. Y11Ni4In9 is a Pauli paramagnet down to 2K. The fibrous microstructure of these compounds leads to a strong anisotropy in their electrical resistivity and magnetization behaviors. The c-axis of the orthorhombic cell is the easy magnetization and high electrical-conductivity direction. Ferrimagnetic-like behavior, with extremely high coercive fields (HC=6.6T for Tb11Ni4In9 at 5K and HC=5.7T for Dy11Ni4In9 at 2K), is found when the fibers (and the c-axis) are oriented parallel to the magnetic field direction; antiferromagnetic-like ground state is observed with the fibers oriented orthogonal (i.e., in the a–b plane). Appearance of a Griffiths phase regime is observed in both compounds before entering the ordered magnetic states. This is more evident for fibers orthogonal to the magnetic field and is even preserved at 1T. Field induced spin-flop magnetic transitions are also observed in Tb11Ni4In9 and Dy11Ni4In9 with fibers orthogonal and parallel to the field, respectively. First principles calculations have been performed for several representative compounds to explain the underlying phase stability and their magnetism.