Evolution of magnetic hardness in the HfFe6Ge6-type RMn6Sn6-xGax and RMn6Sn6-xInx compounds (R=Tb, Dy; 0.2≤x≤1.4)

The HfFe6Ge6-type RMn6Sn6-xX'(x) solid solutions (R=Tb, Dy, X'=Ga, In; xless than or equal to1.4) have been studied by powder magnetization measurements. All the series are characterized by ferrimagnetic ordering and by a decrease in Curie temperatures with the substitution (DeltaT(c)/Deltaxapproximate to-39 K for X'=Ga and DeltaT(c)/Deltaxapproximate to-75 K for X'=In). The RMn6Sn6-xGax systems are characterized by a strong decrease in the spin reorientation temperature with substitution (DeltaT(x) /Deltaxapproximate to -191 K and -78 K for R=Tb and Dy, respectively) while this transition almost does not change in systems containing indium. The coercive fields drastically decrease with the substitution in the TbMn6Sn6-xGax system while the substitution of In for Sn has a weaker effect. The coercive fields of the Dy compounds do not vary greatly with the substitution in both series. The behaviour of the TbMn6Sn6-xGax is compared with the evolutions observed in the TmMn6Sn6-xGax series. This comparison strongly suggests that the replacement of Sn by Ga changes the sign of the A(0)(2) crystal field parameter. (C) 2002 Elsevier Science B.V. All rights reserved.