Magnetic phases in quasi-binary (Fe_1−x Co_x)Ge₂ intermetallic compounds

Abstract

Magnetic neutron diffractometry revealed the existence in (Fe_1−x Co_x)Ge₂ solid solutions (x<0.5) with C16 structure of only two magnetic phases, namely, low-temperature (AFI) and high-temperature (AFII). A third magnetic phase, AFIII, suggested by earlier magnetic measurements, has not been found. The AFI and AFII phases have a commensurate and an incommensurate antiferromagnetic structure with the wave vectors k ₀=2π/a (1,0,0) and k=k ₀+δ k, respectively. The regions of their existence are shown in the magnetic phase diagram. Neutron diffraction measurements yielded the concentration dependence of the average magnetic moment per atom in the antiferromagnetic sublattice of a 3d metal, which, similarly to the dependence of the Néel point on x, was found to be nonlinear. An analysis of these dependences suggests that substitution of cobalt for iron is accompanied, on the one hand, by a decrease of the local spin density on the iron atoms in the nearest environment of a cobalt atom and, on the other hand, by an increase of the effective exchange integral between the nearest-neighbor iron atoms located along the tetragonal axis.