Impact of Ge Doping on Structural and Magnetic Ordering in RMn _x Ga₃ and R₄Mn_1-x Ga_12-y Ge _y (R = Tb, Dy; x 0.25, y 1.0-3.3)

Single crystals of RMn (x) Ga-3 and R4Mn1-x Ga12-y Ge (y) (R = Tb, Dy, x & LE; 0.25, y & AP; 1.0-3.3) were grown from a Ga flux. TheGe dopingleads to a higher Mn content and the formation of a 2 x 2 x2 superstructure. The R atoms order antiferromagnetically below 25K, while the Mn atoms order ferromagnetically at 125-225 Kwith the Ge doping resulting in higher T (C) and partial ferromagnetic ordering of the R atoms below T (C). Single crystals of RMn (x) Ga-3 and their new quaternary derivatives R4Mn1-x Ga12-y Ge (y) (R = Tb, Dy, x & LE; 0.25, y & AP; 1.0-3.3) weregrown from a Ga flux. Thecompounds are derivatives of cubic RGa3 phases, with Mnatoms filling the Ga-6 voids. RMn (x) Ga-3 formally adopts a cubic ABO(3) perovskitestructure, in which the presence of Mn atoms results in a shift ofthe neighboring Ga atoms from their ideal position. A partial substitutionof Ga by Ge leads to a higher Mn content, resulting in structuralordering of the latter and the formation of the superstructure phasesR(4)Mn(1-x )Ga(12-y )Ge (y) , which can be formallydescribed in the Y4PdGa12 structure type. Thepresence of Mn vacancies, which was observed for R = Tb, and Ga/Gemixing lead to a noticeable deviation from the idealized structure.The compounds contain two magnetic sublattices: the R sublattice,which orders antiferromagnetically near 20 K, and the Mn sublattice,which orders ferromagnetically at T (C) =125-225 K with the Ge doping resulting in higher T (C). The two sublattices are not independent, as the Mnsublattice induces partial ferromagnetic ordering of the rare earthatoms below T (C), at least for the Ge-dopedphases. Near T (N), both magnetic susceptibilityand heat capacity reveal complex behavior, indicating changes in magneticstructures below T (N).