Neutron diffraction study of α-Gd₂S₃

Neutron diffraction measurements on a powder sample of α- ¹⁶⁰Gd₂S₃ are performed. This material consists of a stacking of square lattice Gd1 and triangular Gd2 planes and exhibits a novel phase transition that was interpreted as being due to geometrical frustration. The magnetic unit cell is found to be the same as the chemical unit cell. The magnetic moments order parallel with each other along the b-axis. The magnetic structure in the ac plane is such that a Gd1 moment is ordered antiparallel to the nearest neighboring Gd1 moments and is coupled parallel to the next-nearest neighboring Gd1 moments. The Gd2 moment is coupled antiparallel to the nearest neighboring Gd1 moment. The temperature dependence of the order parameter is extracted and is found to be explained rather well by the result of an S = 7/2 molecular field approximation. The collinear structure of the magnetic moments in the triangular lattice and the absence of large magnetic fluctuations around the magnetic transition temperature suggest that the geometrical frustration is not so distinct in α-Gd₂S ₃.