Master thesis defense by Sidse Lærke Lolk

The subgroup of magnetic materials which are subject to geometric frustration experience competing interactions of the spins, thereby suppressing magnetic order, which might give rise to exotic phenomena such as quantum spin liquid phases. Here we investigate the magnetic properties of the frustrated antiferromagnetic S =  ³⁄₂  kagomé system Cr-jarosite KCr₃(SO₄)₂(OH)₆. Deuterated samples of Cr-jarosite were produced by hydrothermal synthesis, and chemical characterization of the samples was performed by 2H nuclear magnetic resonance, thermogravimetric analysis, infrared spectroscopy, powder x-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. The measurements revealed that the combined sample consists predominantly of stoichiometric Cr-jarosite, with 2 % Cr vacancies, and that 18-28 % of K on the A-site is substituted with D_nO. PXRD revealed disordered stacking of the kagomé planes, most likely caused by D₃O⁺. Inelastic neutron scattering experiments were performed on a combined sample using the instruments MARI and LET at ISIS. The neutron spectroscopy revealed a co-existence of magnetic properties in the form of 3D antiferromagnetic ordering and 2D dynamics. The magnetic ordering refutes Cr-jarosite as a potential spin liquid.