Crystal structure and magnetic properties of novel Hf<inf>3</inf>Ni<inf>2</inf>Si<inf>3</inf>-type R<inf>3</inf>Co<inf>2</inf>Ge<inf>3</inf> compounds (R=Y, Sm, Tb–Tm)

The novel R3Co2Ge3 compounds with R=Y, Sm, Tb–Tm adopt the Hf3Ni2Si3-type structure (ordered variant of the Ca3Ga5-type one, space group Cmcm). Sm3Co2Ge3, Tb3Co2Ge3, Ho3Co2Ge3 and Er3Co2Ge3 undergo an antiferromagnetic-type ordering and Tb3Co2Ge3 demonstrates a field-sensitive magnetic behavior. Tm3Co2Ge3 is a pure paramagnet down to 5 K, whereas Y3Co2Ge3 demonstrates Pauli paramagnetism down to ∼120 K. In zero applied field and between ∼50 and ∼15 K Tb3Co2Ge3 shows a non-collinear antiferromagnetic ordering with wave vectors K0=[0, 0, 0] and K1=[±1/3, 0, 0] and a magnetic unit cell 3aTb3Co2Ge2×bTb3Co2Ge3×cTb3Co2Ge3, whereas below ∼15 K it exhibits a complex antiferromagnetic ordering with K0=[0, 0, 0], K1=[±1/3, 0, 0] and K2=[1/2, 0, 0] wave vectors and magnetic unit cell 6aTb3Co2Ge2×bTb3Co2Ge2×cTb3Co2Ge2.