Magnetic structures and phase transitions in PrMn2-xFexGe2

The magnetic properties and magnetic structures of PrMn2-xFexGe2 compounds (space group I4/mmm) have been investigated using magnetic, Fe-57 Mossbauer effect (x=1.0,1.3,1.6), and neutron diffraction measurements (x=0.4,0.6,0.8,1.3) over the temperature range of 3-410 K. This has enabled the existing magnetic phase diagram for PrMn2-xFexGe2 to be extended from Fe concentration x=0-1 to the full range x=0-2 in terms of concentration and d(Mn-Mn), the intralayer distance. Analysis of the Mossbauer spectra (4.5-300 K) using a model which takes nearest-neighbor environments into account confirms the nonmagnetic nature of Fe atoms in these compounds, and leads to hyperfine parameters which deviate around the magnetic transition temperatures derived from the magnetic and neutron investigations while also enabling the Debye temperatures of PrMn2-xFexGe2 (x=0.4-1.6) to be determined. The experimental values for T-C(inter) are found to decrease rapidly with increasing Fe concentration in the range x=0.0-0.6 compared with calculated T-C(inter) values due to pressure (and therefore geometric) effects only. This behavior demonstrates that electronic effects and replacement of the magnetic Mn atoms with nonmagnetic Fe atoms contribute to the overall magnetic behavior of PrMn2-xFexGe2 compounds. Compared with intralayer Mn-Mn interactions, the interlayer Mn-Mn interactions play the major role in the anomalous thermal expansion observed at magnetic transition in these layered systems, with the interlayer Mn-Mn interactions governing the significant magnetovolume effects.