This paper describes a computer program, based on the theory of groups and representations, which calculates symmetry‐adapted functions used for the description of various ordered structures in crystals. It is assumed that the ordered structure, which is formed by a configuration of occupational probabilities, ion displacements, magnetic moments, quadrupolar moments or other local physical quantities, is obtained from a high‐symmetry crystal structure with a given space group G, as a result of a symmetry‐lowering phase transition. The detailed characteristics of the phase transition are given by the specification of the irreducible representations of group G, active in the transition. The symmetry‐adapted functions obtained from the calculation are perfect tools for the construction of model structures, which can be used for comparison with experimental (e.g. neutron diffraction) data, and can be a great help in numerical data elaboration by reducing the number of adjustable parameters describing the structure of a given symmetry.
Neutron diffraction studies of polycrystalline R3Cu4Sn4
(R = Tb,
Dy, Ho, Er) intermetallic compounds with the orthorhombic Gd3Cu4Ge4-type
crystal structure indicate the existence of different magnetic structures.
Rare earth atoms occupy two non-equivalent 2d and 4e sublattices. The
rare earth magnetic moments order at low temperatures. For R = Tb
and Dy the magnetic structures below the Néel temperature are described
by the propagation vectors k = (0, 0, 1/2 + δ).
In these compounds both rare earth sublattices order. For R = Ho the
magnetic structure is more complicated. There are two vectors; one of them is k = (0, 1/2, 0)
whereas the second one changes with temperature. For the Er
compound there is the propagation vector k = (1/2, 1/2, 0)
which describes the magnetic ordering in the 2d sublattice and at low
temperatures is accompanied by the propagation vector k = (0, 0,δ)
describing the ordering in the 4e sublattice.
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