119Sn Mössbauer spectroscopy study of the magnetic properties of the HfFe6Ge6-type compounds: SmMn6Sn4Ge2 and GdMn6Sn4Ge2

The HfFe6Ge6-type compound SmMn6Sn4Ge2 has been studied by single-crystal magnetisation and 119Sn Mössbauer spectroscopy. The compound orders ferromagnetically at Tc = 420 K and displays an easy-axis anisotropy from Tc to TSR = 130 K. Below TSR, both magnetisation and 119Sn Mössbauer spectroscopy measurements indicate a deviation from the [0 0 1] direction and the presence of easy-cone anisotropy. The angle of the moments with respect to the [0 0 1] direction is estimated to 26–31° from Mössbauer spectroscopy results, in good accordance with the magnetisation results. The isotypic compounds GdMn6Sn4Ge2 and GdMn6Sn6 studied by 119Sn Mössbauer spectroscopy display easy plane anisotropy in the whole temperature range 300–4.2 K. The anisotropy behaviours of the LMn6Sn4Ge2 compounds are discussed and the coexistence of easy cone anisotropy for both the SmMn6Sn4Ge2 and HoMn6Sn4Ge2 suggests the play of a positive second-order anisotropy constant of the Mn sublattice.

Research highlights
► Evidence of moment reorientation by single crystal magnetisation measurement.
► Analysis of the reorientation by 119Sn Mössbauer spectroscopy.
► Evidence of anisotropic field transfer from the Mn sublattice to the Sn nucleus.
► Unusual thermal evolution of the magnetocrystalline anisotropy.