The crystallographic phases and magnetic properties of Fe₂MnSi_1−xGe_x

Fe2MnSi1xGex (x ¼ 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 10 h of milling. The X-ray data reveal that in the high-temperature annealing the single D03-type phase can be retained up to 50% substitution of Ge for Si in Fe2MnSi. A metastable D03 phase is obtained after crystallization of the as-milled amorphous compounds with x > 0:5: High-temperature annealing transforms the low-temperature D03 phase into a single D019 phase (x ¼ 1) or a mixture of D03 and D019 phase (x ¼ 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 D03 phase to the D019 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.