From Fe_32+δGe_35-xP_x to Fe_32+δGe_35-x-yP_xAs_y: Fine geometry optimization in new intergrowth structures

A new compound with a two-dimensional intergrowth structure, Fe_32+δGe_35-xP_x (x = 1.7–4.4, δ = 0.6–0.75), and the solid solution on its base, Fe_32+δGe_35-x-yP_xAs_y (δ < 0.2, x = 0–4.4, y = 0–2), were obtained by the two-stage synthesis from elements. The crystal structure of Fe_32+δGe_35-xP_x can be described as an alternation of infinite columns of two intermetallic structure types: MgFe₆Ge₆ and Co₂Al₅. The characteristic feature of Fe_32+δGe_35-xP_x is that P partially replaces Ge in one of the 6k sites in the MgFe₆Ge₆-type column and does not form the X₂ dumbbells consisting of As atoms that are present in Fe_32+δGe₃₃As₂. In the Fe_32+δGe_35-x-yP_xAs_y solid solution, P and As atoms occupy the same sites as in the initial Fe_32+δGe_35-xP_x and Fe_32+δGe₃₃As₂ compounds, respectively. The magnetic behavior of Fe_32+δGe_35-xP_x is similar to that of Fe_32+δGe₃₃As₂, and the antiferromagnetic transition is observed at T_N ∼130 K.