  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 TN ~ 155 K, two low-temperature
transitions at T1 ~ 21 K and T2 ~ 27 K were identified. The Fe moments order at
TN with an incommensurate propagation vector (tau,tau,0) with tau varying
between 0.06 and 0.14 as a function of temperature, and maintain this order
over the entire T<TN 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.
