Magnetic materials with geometrically frustrated lattices are known to exhibit remarkable sensitivity to small perturbations that could favor certain states among their highly degenerate ground-state manifold. Examples of such perturbations include the thermal fluctuations, single-ion anisotropy, Dzyaloshinskii-Moriya and dipolar interactions, magnetoelastic coupling or disorder. I will discuss the effect of atomic disorder in the interlayer coupling of two classes of two-dimensional lattices, with triangular and honeycomb geometries. Results of elastic and inelastic neutron scattering experiments are presented. One case study involves the hole-doped crednerite system Cu(Mn1−xCux)O2, made of stacked triangular layers of magnetic Mn3+ ions positioned in an edge-sharing octahedral coordination [1,2]. The successive [MnO2]- layers are connected by nonmagnetic Cu planes, where the Cu+ is in a linear stick coordination with the oxygens above and below. The undoped compound CuMnO2 was found to exhibit a magneto-elastic stabilization of a long-range magnetic ordering below approximately 65 K. The neutron scattering study shows that a small deviation from the stoichiometric composition results in a significant impact on the magnetoelastic properties of the system and induces a gradual relaxation of the effective dimensionality of the magnetic lattice. A second case study deals with the honeycomb lattice system Na2+xNi2TeO6 [3,4]. The structure of this material is similar to that of the layered NaNiO2, but 1/3 of the sites of the triangular lattice are occupied in an ordered manner by non-magnetic Te cations. The TeO6 octahedron sits in the center of a honeycomb unit composed of NiO6 octahedra. The magnetic honeycomb layers are separated by the nonmagnetic layers of Na. In this system, the diffusive Na atoms provide an effective control of the interlayer magnetic couplings, and therefore a tuning of magnetic lattice dimensionality. The changes in the static magnetic order and spin-dynamics spectrum are probed by neutron scattering for two different Na2+xNi2TeO6 samples with different Na content.

Tuning the effective dimensionality of triangular-based magnetic lattices by control of stoichiometry

2019 Spring National Meeting

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