Neutron diffraction and symmetry analysis of magnetic structures in dysprosium iron garnet

Complete text of publication follows. High resolution powder neutron diffraction experiment has been performed at ILL on dysprosium iron garnet (DyIG) compound, in the temperature range 1.5 - 300 K. The room temperature pattern show only the reflections of the cubic structure of the space group I a - 3 d. The magnetic contribution is superimposed to the nuclear associated to the propagation vector K = [000]. The magnetic intensities are well interpreted with the collinear ferrimagnetic Neel model which appears at TN = 563 K. The low temperature patterns (below 100 K) exhibit several superstructure reflections forbidden by the local symmetry of the 24 d rare earth site associated to an antiferromagnetic component of Dy moment. The resulting magnetic configuration is complex and of umbrella-type [1]. The magnetic structures are discussed using the representation analysis of the cubic space group I a - 3 d and subgroup R - 3 c. Below 14 K, magnetic modes belonging to the irreducible representation of the monoclinic space group C 2/c are necessary to explain the observed magnetic structure. (author) [1] M. Lahoubi, M. Guillot, A. Marchand, F. Tcheou, E. Roudault, IEEE Trans. Magn., 20 (1984) 1518