Atomic and magnetic structure of Mn5–xFexSi3

Revised magnetic phase diagram for FexMn5−xSi3 intermetallics

“…Magnetization and neutron data reported 11 for Fe 3 Mn 2 Si 3 imply that magnetic order occurs below 77 K. The magnetization data of Songlin et al 1 however give a higher Curie point, at about 250 K, followed by a low temperature transition at 50 K. The present neutron results are in contrast with both of these findings. There is no difference between the patterns in the paramagnetic phase and at 200 K. Below 150 K, a magnetic peak is observed at approximately 2.15 Å.…”

“…The best fit was obtained with moments aligned at approximately 40°to the c axis, a detail of the magnetic order that has not been reported previously. 11 The average refined moments at 8 K for the 4d and 6g sites are 1.4 B and 2.5 B , respectively. These moments are substantially higher than the site moments for Fe 5 Si 3 .…”

“…The observation by Binczycka et al 11 of a helical spin structure in Fe 3 Mn 2 Si 3 below 77 K with a spiral period of 30 Å prompted us to see if a low temperature spiral phase exists for compositions richer in Fe. The Curie temperature is 265 K and at 150 K the magnetic structure is similar to that of Fe 4 MnSi 3 , with moments of 0.9 B and 1.9 B for 4d and 6g sites, respectively.…”

“…These results concur exactly with previous determinations by Mössbauer spectroscopy 5 and neutron diffraction. 11 The preference of Fe for the 4d site is possibly due to a more stable Fe metalmetal bond at this site. 5 The room temperature lattice parameters display an approximately linear increase with increasing Mn concentration ͑Ϸ0.022 Å/Mn atom for a and Ϸ0.017 Å/Mn atom for c͒, in good agreement with the lattice parameters quoted by Johnson et al 5 and Aronsson.…”

“…Magnetic interactions in Mn 5 Si 3 are extremely sensitive to Mn-Mn interatomic distances and give rise to a complex antiferromagnetic structure which has been extensively investigated by both powder and single crystal neutron diffraction. [6][7][8][9][10] Transitions from antiferromagnetic to ferromagnetic ordering across the series were investigated by Binczycka et al 11 In particular, in the Fe rich region of the phase diagram, these authors reported a helical spin structure for Fe 3 Mn 2 Si 3 with a spiral period of 30 Å along the c axis and a collinear c axis ferromagnetic alignment for Fe 4 MnSi 3 . A moderate magnetic entropy change of 4 J kg Ϫ1 K Ϫ1 reported for Fe 4 MnSi 3 1 has prompted us to reinvestigate in detail the magnetic phase diagram by neutron powder diffraction.…”