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We use polarized xyz neutron diffraction to examine the nature of the freezing transition to an unconventional topological spin-glass state in the Sϭ5/2 kagomé antiferromagnet (D 3 O)Fe 3 (SO 4 ) 2 (OD) 6 . Measurements of the total magnetic scattering cross-section, S(Q), were taken in the momentum-transfer range 0.5 рQр2.5 Å Ϫ1 between the temperatures 1.5 and 250 K. The observation of two-dimensional correlations at 250 K, i.e., in excess of 14 times the freezing temperature, is in agreement with predictions of an anisotropyinduced spin-glass freezing transition in an ordered kagomé antiferromagnet.

Internal magnetic structure of dextran coated magnetite nanoparticles in solution using small angle neutron scattering with polarization analysis J. Appl. Phys. 109, 07B513 (2011); 10.1063/1.3540589Theoretical studies on the structure of interacting colloidal suspensions by spin-echo small angle neutron scattering Small-angle neutron scattering study of structural changes in temperature sensitive microgel colloids Small angle neutron scattering experiments from colloidal dispersions at rest and under sheared conditionsIn this article we describe apparatus for the study of the microwave-driven growth of particles in solution by in situ small angle neutron scattering ͑SANS͒. This apparatus has enabled the first preliminary experiments using microwave-activated in situ diffraction. We take iron oxide as the prototype system, but the technique may be extended to a wide variety of chemical reactions that deposit solids from solution. The key features of the apparatus are a microwave cavity with a modular construction that may be adapted to the geometric constraints of the diffractometer, and a computer-controlled microwave generator that may be set to maintain either constant pressure or temperature in the reaction vessel. In this particular piece of equipment the reaction vessel is adapted so that part of the sample fills a cell of identical construction to those commonly used in SANS measurements for optimal transmission of the neutron beam.

We report an inelastic neutron scattering study of coherent magnetic excitations in powder and single-crystal samples of the model kagome antiferromagnet potassium iron jarosite, KFe3(OH)6(SO4)2. Initial measurements on a natural single crystal using a triple-axis spectrometer revealed a mode with a zone-centre gap of 7 meV that showed little dispersion within the kagome layers, as well as some indication of a mode with a zone-boundary energy of approximately 20 meV. However, the high background from hydrogen in the sample made it very difficult to search for other excitations. In the absence of suitable deuterated crystals, measurements were performed on deuterated powders using time-of-flight neutron spectrometers over a range of temperatures that include . This confirmed the flat 7 meV mode as well as dispersive modes that reached to higher energies. The origin of these modes is discussed in relation to the most likely Hamiltonian for the magnetic degrees of freedom in this material, and estimates are made of the strength of the nearest-neighbour exchange, J1, and contributions from a Dzyaloshinsky–Moriya interaction or single-ion anisotropy arising from a crystal field.

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