Inelastic neutron scattering study of magnetic excitations in the kagome antiferromagnet potassium jarosite

Abstract

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.

Determination of the single-ion anisotropy energy in aS=52kagome antiferromagnet using x-ray absorption spectroscopy

“…The energy of D z = 0.5͑1͒ meV for the easy-plane singleion anisotropy is in good agreement with the values found by Matan et al 24 ͓0.428͑5͒ meV͔ and Coomer et al 25 ͓0.47͑2͒ meV͔ in their spin-wave analysis of inelastic neutron data from single crystals and powders, respectively. This implies that an easy-plane anisotropy, along with further-neighbor interactions, can explain the magnetic ground state in potassium iron jarosite.…”

“…The DMI term has shown to be symmetry allowed on the kagome lattice and has been argued to prevail over the CF anisotropy in the spherical ͑L =0͒ 3d 5 Fe 3+ ion. 23 Fits to the spin-wave dispersion curves measured with neutron spectroscopy on single crystal 24 and powder samples 25 of potassium jarosite have found to be slightly better in a model with DMI compared to the model with CF anisotropy. The evi-FIG.…”

Quantum magnetism in minerals

“…They arrived at the slightly modified values of Hamiltonian parameters (J 1 = 3.225, J 2 = 0.11, D z = −0.195, and |D p | = 0.218 meV) and argued in favour of the DMI model as opposed to the CF model, as one would not expect the single-ion anisotropy D for the Fe 3+ ion to be as high as 10% of J 1 . Shortly afterwards, another set of INS measurements on the K-Fe-jarosite has been published by Coomer et al [301]. In this work, both a natural single crystal and a synthetic deuterated powder sample have been used.…”

Scale-Free Antiferromagnetic Fluctuations in thes=1/2Kagome Antiferromagnet Herbertsmithite

“…Of the many kagome systems studied experimentally, including the jarosites [14,15] [19,20]. The Weiss temperature is 300 K and the AF exchange interaction J ≈ 190 K [6,20] 6 Cl 2 with 0 < x ≤ 1.…”