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

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, T_C, of 112 and 88 K, respectively. Y₁₁Ni₄In₉ is a Pauli paramagnet down to 2 K. 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 (H_C = 6.6 T for Tb₁₁Ni₄In₉ at 5 K and H_C = 5.7 T for Dy₁₁Ni₄In₉ at 2 K), 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 1 T. 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