The crystallographic phases and magnetic properties of Fe2MnSi1-xGex

Fe2MnSi1-xGex (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1) compounds were prepared by a mechanically activated solid-state diffusion method. Both X-ray diffraction and differential scanning calorimetry evidenced the presence of an amorphous phase after 10h of milling.-The X-ray data reveal that in the high-temperature, annealing the single DO3-type phase can be retained up to 50% substitution of Ge for Si in Fe2MnSi. A metastable D0(3) phase is obtained after crystallization of the as-milled amorphous, compounds with x > 0.5. High-temperature annealing transforms the low-temperature D0(3) phase into a single D0(19) phase (x = 1) or a mixture of D0(3) and D0(19) phase (x = 0.6 and 0.8). Low-field thermomagnetic measurements show a moderately sharp ferromagnetic-paramagnetic transition, which becomes enormously broad in higher magnetic fields. The Curie temperature is significantly enhanced when going from the D0(3) phase to the D0(19) phase. Neither a magnetic-field-induced transition nor a reversible structural transition is observed throughout this compound series. The magnetocaloric effect associated with the magnetic transition is small. (C) 2002 Elsevier Science B.V. All rights reserved.