Rhombohedrally distorted γ-brasses Cr(1-x)Fe(x)Ga.

A series of rhombohedrally distorted γ-brass structures containing a mixture of magnetically active 3d elements, Cr and Fe, Cr(1-x)Fe(x)Ga, is investigated crystallographically. These structures consist of chains of trans-face-sharing Ga-centered transition metal icosahedra. Neutron powder diffraction specifically on Cr(0.5)Fe(0.5)Ga, which could be prepared as a single phase material, gave lattice constants (11 K) a = 12.5172(2) Å and c = 7.8325(2) Å and a refined composition of Cr(0.502(6))Fe(0.498)Ga = Cr(6.523)Fe(6.477)Ga(13) and revealed partial ordering of Cr and Fe atoms among three crystallographic sites. Magnetic susceptibility and magnetization studies of Cr(0.5)Fe(0.5)Ga showed the onset of magnetic ordering at ca. 25 K. Theoretical calculations suggested both site-energy and bond-energy factors influencing the Cr/Fe distribution. Heteroatomic interactions significantly affect exchange interactions and create low local magnetic moments. Models created to mimic Cr(0.5)Fe(0.5)Ga showed ferromagnetic Fe-Fe and antiferromagnetic Cr-Fe interactions, with an overall ferrimagnetic ordering.