Impact of Ge Doping on Structural and Magnetic Ordering in RMn x Ga 3 and R 4 Mn 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 their new quaternary derivatives R 4 Mn 1- x Ga 12- y Ge y (R = Tb, Dy, x ≤ 0.25, y ≈ 1.0-3.3) were grown from a Ga flux. The compounds are derivatives of cubic RGa 3 phases, with Mn atoms filling the Ga 6 voids. RMn x Ga 3 formally adopts a cubic ABO 3 perovskite structure, in which the presence of Mn atoms results in a shift of the neighboring Ga atoms from their ideal position. A partial substitution of Ga by Ge leads to a higher Mn content, resulting in structural ordering of the latter and the formation of the superstructure phases R 4 Mn 1- x Ga 12- y Ge y , which can be formally described in the Y 4 PdGa 12 structure type. The presence of Mn vacancies, which was observed for R = Tb, and Ga/Ge mixing 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 Mn sublattice induces partial ferromagnetic ordering of the rare earth atoms below T C , at least for the Ge-doped phases. Near T N , both magnetic susceptibility and heat capacity reveal complex behavior, indicating changes in magnetic structures below T N .