Master thesis defense by Mathilde Borup Sørensen

In this master thesis the difference between the 3D long-range ordered frustrated kagomé antiferromagnet potassium jarosite and the disordered spin-glass deuteronium jarosite is studied with the goal of gaining insight into why deuteronium jarosite does not exhibit long-range 3D order. ²H MAS NMR and PXRD were used to chemically characterise the samples. The deuteronium sample was shown to have 95.1±1.3% iron occupancy and less than ideal occupancy of the D₃O⁺-site. Susceptibility measurements were performed on deuteronium jarosite and showed a spin-glass transition at 14 K. The magnetism of both compounds was examined with neutron scattering. Inelastic measurements were carried out on the Time-of-Flight spectrometer FOCUS at PSI, and neutron diffraction was performed at neutron diffractometer HRPT. Potassium jarosite was found to order magnetically and had a lifted zero-energy mode at ∼ 7 meV. Deuteronium jarosite showed no indication of magnetic Bragg peaks in data from both FOCUS and HRPT. Instead FOCUS measurements revealed dynamic 2D short range magnetic correlations with correlation length ξ = 4.8−6.7 Å below ≈ 0.8 meV. The centre of the scattering was found to reside between Q = 1 Å and Q = 1.1 Å, which is the Q-value of the first 3D magnetic peak in jarosites.