A magnetisation study of TmMn6Sn6−xGax single crystals (0.15⩽x⩽1.90)

Single crystals of HfFe6Ge6-type TmMn6Sn6−xGax compounds (1.90⩾x⩾0.15) have been prepared by a flux method and analyzed by thermomagnetic and high-field magnetisation measurements. At low temperature, all the compounds display spontaneous magnetisation (Msat≈25 Am2/kg): the compounds with a low Ga content (x⩽0.51) are characterised by an easy plane magnetisation, whereas the compounds with a higher Ga content (x⩾0.66) are characterised by an easy axis magnetisation. The analysis of the magnetisation curves enable a determination of the anisotropy constants. It is observed that K1 increases with the gallium concentration from -1.14×106 J/m3 for xGa=0.15 to 2.28×106 J/m3 for xGa=1.22. The constant K2 displays weakly positive or negligible values (K2⩽0.47×106 J/m3).