Intricate magnetic behavior of Fe6Ge5 and its origin within a complex iron framework: The magnetic and 57Fe Mössbauer study

Fe6Ge5 was synthesized from the elements both as single crystals and a polycrystalline powder. Its crystal structure was reinvestigated in a wide temperature range using high-resolution powder and single-crystal X-ray diffraction. The crystal structure of Fe6Ge5 is connected with those of other iron germanides and features an alternation of iron-rich and germanium-rich layers. The magnetic behavior was studied by magnetization measurements on a single crystal and 57Fe Mössbauer spectroscopy. The results of both methods showed that a peculiar two-step antiferromagnetic ordering (TN1 = 110 K, TN2 = 330 K) takes place, with the part of iron magnetic moments remaining disordered between the transitions. Such behavior originates from the large number of both symmetrically and locally distinct iron atoms that form a weakly connected iron framework and yield the competition between ferromagnetic and antiferromagnetic interactions.