Distinct order of Gd 4f and Fe 3d moments coexisting in GdFe₄Al₈

Single crystals of flux-grown tetragonal GdFe₄Al₈ were characterized by thermodynamic, transport, and x-ray resonant magnetic scattering measurements. In addition to antiferromagnetic order at T_N≈155 K, two low-temperature transitions at T₁≈21 K and T₂≈27 K were identified. The Fe moments order at T_N with an incommensurate propagation vector (τ,τ,0) with τ varying between 0.06 and 0.14 as a function of temperature, and maintain this order over the entire T<T_N range. The Gd 4f moments order below T₂ with a ferromagnetic component mainly out of plane. Below T₁, the ferromagnetic components are confined to the crystallographic plane. Remarkably, at low temperatures the Fe moments maintain the same modulation as at high temperatures, but the Gd 4f moments apparently do not follow this modulation. The magnetic phase diagrams for fields applied in [110] and [001] direction are presented and possible magnetic structures are discussed.