Magnetostructural phase transitions of DyFe4Ge2: Part I—By XRPD

Abstract We present the temperature phase diagram of the compound DyFe 4 Ge 2 determined from high-quality powder XRPD for the entire magnetically ordered regime. DyFe 4 Ge 2 undergoes at T N , T c = 55 K a simultaneous structural and magnetic transition of second-order P4 2 /mnm , T N , T c = 55 K → Cmmm , followed by two subsequent isostructural first-order magnetic transitions at T ic 2 = 45 K and T ic 1 = 28 K . The structural transition at T N , T c is characterised by strong changes of the a / b ratio and of the shear strain while the T ic 1 = 28 K transition is related to a lattice expansion along c 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 T ic 1 = 28 K - T ic 2 = 45 K of incommensurate magnetic phases.