Magnetic properties and electronic structure of the new HfFe6Ge6-type HfMn6Ge6 compound

Magnetisation measurements, neutron diffraction experiments and electronic structure calculations have been performed on the new HfFe6Ge6-type (P6/mmm) HfMn6Ge6 compound. This compound orders antiferromagnetically below TN = 650 K in a collinear easy-axis antiferromagnetic arrangement and undergoes a second transition at Tt = 30 K into an incommensurate double-cone antiferromagnetic structure where the Mn moments (mMn = 2.20μB at 2 K) slightly deviate from the c-axis. The computed electronic structure is characterised by a low density of states at the Fermi level and by a marked anisotropy in the band structure. The effect of partially substituting Ga for Ge on the magnetic properties is also investigated. The ordering temperature of the pseudo-ternary HfMn6Ge6−xGax compounds (0 < x ≤ 1) is found to decrease upon Ga substitution while the antiferromagnetic order is preserved in the whole ordered temperature range. The results are compared with previously published data concerning other RMn6Ge6 and RMn6Ge6−xGax representatives.