Magnetic phase transitions in ScFe4Al8 by powder and single crystal neutron diffraction

Unpolarized neutron diffraction and magnetization experiments have been performed on single crystal of ScFe4Al8 intermetallic compound. In the single crystal both, neutron and high resolution X-ray diffraction measurements, indicate perfect crystallochemical order. The magnetic ordering was studied in the temperature range 8-250 K. LT neutron measurements show that the compound exhibits magnetic spiral structure. The scandium seems magnetically inactive while the iron site splits into two independent magnetic orbits. Below 115 K two sets of magnetic reflections were found. Each of them requires different wave vector representation i.e. (q) over right arrow (1) = (0.13, 0.13, 0) and (q) over right arrow (2) = (0. 18, 0.18, 0) and discloses different temperature behavior. In the basic elementary cell, the Fe moments of adjacent atoms along c axis are forming a constant angle while along the face diagonals the mutual orientation of magnetic moments is almost antiparallel. The iron moments rotate within the basal plane upon entering the neighboring cell. The magnetic structure with two modulation vectors is different from the one observed earlier by means of magnetic neutron powder diffraction, where only one modulation vector was observed. The reasons of this different magnetic behavior are discussed.