Impact of Ge Doping on Structural and Magnetic Ordering in RMnGa and RMnGaGe (R = Tb, Dy; ≤ 0.25, ≈ 1.0-3.3).

Single crystals of RMnGa and their new quaternary derivatives RMnGaGe (R = Tb, Dy, ≤ 0.25, ≈ 1.0-3.3) were grown from a Ga flux. The compounds are derivatives of cubic RGa phases, with Mn atoms filling the Ga voids. RMnGa formally adopts a cubic ABO 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 RMnGaGe, which can be formally described in the YPdGa 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 = 125-225 K with the Ge doping resulting in higher . The two sublattices are not independent, as the Mn sublattice induces partial ferromagnetic ordering of the rare earth atoms below , at least for the Ge-doped phases. Near , both magnetic susceptibility and heat capacity reveal complex behavior, indicating changes in magnetic structures below .