Structural and Magnetic Properties of Mn 2 GeSe 4

Mn 2 GeSe 4 is one of the rare ternary transition metal selenides which crystallizes in the olivine structure‐type (space group Pnma no. 62, Z = 4) with the room‐temperature lattice parameters a = 13.350(3) Å, b = 7.765(2) Å, c = 6.307(1) Å. The crystal structure is based on a hexagonal close packing of Se 2‐ with Mn 2+ ions in octahedral and Ge 4+ ions in tetrahedral coordination. Between 350 K and 150 K the magnetic susceptibility of Mn 2 GeSe 4 is characterized by a Curie‐Weiss‐behaviour with an effective moment of 5.90(3) μ Bohr indicative for Mn 2+ ions with a 3 d 5 configuration ( S = 5/2) and a paramagnetic Curie temperature of ‐240(5) K indicating predominant antiferromagnetic coupling between the Mn 2+ ions with a significant deviation from linear behaviour of 1/χ towards lower temperatures. At 66 K a sudden drop of 1/χ is observed which we ascribe to the onset of long‐range magnetic ordering.