Magnetostructural phase transitions of DyFe4Ge2: Part I—By XRPD

We present the temperature phase diagram of the compound DyFe4Ge2 determined from high-quality powder XRPD for the entire magnetically ordered regime. DyFe4Ge2 undergoes at TNTN, Tc=55K a simultaneous structural and magnetic transition of second-order P42/mnm  , TNTN, Tc=55K→Cmmm, followed by two subsequent isostructural first-order magnetic transitions at Tic2=45K and Tic1=28K. The structural transition at TNTN, TcTc is characterised by strong changes of the a/ba/b ratio and of the shear strain while the Tic1=28K transition is related to a lattice expansion along cc on cooling. Minor Fe parameter shifts and deformations (torsion angle and out-of plane Fe–Fe distances) of the Fe tetrahedra were found to accompany the two magnetic transitions. Using the XRPD instrumental resolution and modelling the anisotropic micro-strain enabled us to refine the observed anisotropic peak broadening associated with the presence of micro-structure effects. The maximum strain experienced by the crystal lattice during a sequence of subtle magnetic transitions was observed in the intermediate temperature interval Tic1=28K-Tic2=45K of incommensurate magnetic phases.