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

Abstract The magnetic structure of the tetragonal antiferromagnetic LuFe 4 Ge 2 and YFe 4 Si 2 compounds has been studied by high resolution neutron and X-ray diffraction above and below the magneto-elastic transition at T N , T c =32 K and 76 K, respectively. Below T N , T c the tetragonal high temperature ( HT ) phase transforms into the low temperature ( LT) orthorhombic magnetic phase: P 4 2 /mnm (HT) → Pnnm ( q= 0) ( LT ) with a 2D canted moment arrangement of the Fe moments within the (001) plane with the magnetic space group P 2 1 n ' 2 1 n ' 2 1 m ' ( S h 58 399 ) . The Fe magnetic moment value is highly reduced in both compounds due to the presence of geometrical and exchange frustration relating to the underlying crystal structure comprising columns of Fe tetrahedra expanding along the c direction with antiferromagnetic interactions. The magnetic refinements were perturbed by the presence of partly unidentified impurity phases mainly in YFe 4 Si 2 .