Magnetic study of ${\mathrm{PrFe}}_2$${\mathrm{Si}}_2$ and ${\mathrm{PrFe}}_2$${\mathrm{Ge}}_2$ compounds by susceptibility measurements, neutron diffraction, and Mössbauer spectroscopy

The magnetic properties of the tetragonal (${\mathrm{ThCr}}_2$ ${\mathrm{Si}}_2$- type) ${\mathrm{PrFe}}_2$ ${\mathit{X}}_2$ (X=Si,Ge) compounds have been investigated using magnetization, neutron-diffraction and ${}_{}{}^{57}{}_{}{}^{}\mathrm{spectroscopy}$ measurements. ${\mathrm{PrFe}}_2$ ${\mathrm{Si}}_2$ and ${\mathrm{PrFe}}_2$ ${\mathrm{Ge}}_2$ were shown to order antiferromagnetically (AF) at 7.70 and 14.2 K, respectively. Neutron and Mössbauer transferred-fields data indicate the occurrence of a type-II AF structure (++--) with the moment aligned along the c axis in both compounds but with quite different saturation moments: 1.41 (Si) and 2.75${\mathrm{\mu }}_{\mathit{B}}$ (Ge) at 1.3 K. In addition, ${\mathrm{PrFe}}_2$ ${\mathrm{Ge}}_2$ presents a transition towards an incommensurate modulated structure at 9 K. The results are discussed in the frame of a crystal-field model.