Magnetoelastic phase transitions in the LuFe4Ge2 and YFe4Si2 compounds: A neutron diffraction study

► Magnetic phase diagrams of LuFe4Ge2 and YFe4Si2 compounds studied by neutron and X-ray diffraction. ► The HT tetragonal phases undergo magnetoelastic transitions below TN,TC=32 K and 76 K respectively. ► Both phase diagrams comprise ranges of distinct symmetry: HT (P42/mnm), LT (Pnnm) orthorhombic. ► The LT phases (Pnnm, q=0) correspond to planar canted Fe moment arrangements within the (001) plane. ► The Fe moment values are highly reduced due to geometrical and exchange frustration.