Magnetostructural phase transitions of DyFe4Ge2: Part II Neutron diffraction

We present the temperature magnetic phase diagram of the compound DyFe4Ge2 determined from neutron diffraction data for the entire magnetically ordered regime. DyFe4Ge2 undergoes at TN,Tc=55K a simultaneous structural and magnetic transition of second order (or weakly first order) followed by two subsequent isostructural first-order magnetic transitions at Tic2=45K and Tic1=28KTic1=28K: P42/mnm,TN,Tc=55K→Cmmm,q1=(0120)Tic2=45K→q2=(0qy0)Tic1=28K→q1. The re-entrant lock-in magnetic phase q1=(0120) is stable in the high-temperature range Tic2–TN and in the low-temperature range 1.5 K–Tic1 while the incommensurately modulated q2=(0qy0) magnetic phase is sandwiched in the intermediate range Tic1–Tic2 between the two commensurate phases. The wave vector q2 has a temperature-dependent length with a minimum in the middle of the incommensurate range and corresponds to a multiaxial amplitude modulated phase. Symmetry analysis leads for both propagation vectors in Cmmm to a twofold and fourfold splitting of the tetragonal Dy 2b site and the Fe 8i   sites, respectively. The low temperature q1=(0120) and the q2=(0qy0) phases correspond to 3D canted magnetic structures described by the irreducible representations (Irreps) Γ2+Γ3Γ2+Γ3 while the high-temperature q1 phase to 2D canted magnetic structures described by a single Irrep ΓΓ2. The Tic2 transition is connected with reorientations of both Fe and Dy moments.