Magnetic properties of the ternary sulfide Na6MnS4

The characteristic structural feature of the ternary sulfide Na6MnS4 is isolated, hardly distorted [MnS4]-tetrahedrons (space group P6(3)mc). Measurements of the magnetic susceptibilities down to low temperatures yield a behaviour according to the Curie-law (mu=5.93(2) mu(B)). Only below 4 K can deviations be detected indicating anti-ferromagnetic interactions. However, neutron diffraction experiments at 1.7 K did not show a magnetic ordering. Additional measurements under the influence of an external magnetic field (>10 kOe) lead to a ferromagnetic spin structure. An experiment, in which the external magnetic field of 50 kOe was turned off at a constantly kept temperature of 1.7 K, indicates the formation of an anti-ferromagnetic spin structure, with a unit cell volume six times larger than that of the crystallographic structure. The Neel temperature of this anti-ferromagnetic phase was determined to be 4.7(2) K. After cooling, it was observed that the anti-ferromagnetic spin structure, once again, could only be detected after a ferromagnetic order was induced in advance. (C) 2002 Elsevier Science B.V. All rights reserved.