Klaus Habicht

Direct measurement of the spin Hamiltonian and observation of condensation of magnons in the 2D frustrated quantum magnet Cs2CuCl4.

We propose a method for measuring spin Hamiltonians and apply it to the spin- 1/2 Heisenberg antiferromagnet Cs2CuCl4, which shows a 2D fractionalized resonating valence bond state at low fields. By applying strong fields we fully align the spin moment of Cs2CuCl4, transforming it into an effective ferromagnet. In this phase the excitations are conventional magnons and their dispersion relation measured using neutron scattering give the exchange couplings directly, which are found to form an anisotropic triangular lattice with small Dzyaloshinskii-Moriya terms. Using the field to control the excitations we observe Bose condensation of magnons into an ordered ground state.

Magnetic ordering and negative thermal expansion in PrFeAsO

We report the structure and magnetism of PrFeAsO, one of the parent phases of the Fe-As family of superconductors, as measured by neutron powder diffraction. In common with other REFeAsO materials, a tetragonal-orthorhombic phase transition is found on cooling below 136 K and striped Fe magnetism with

Gains from the upgrade of the cold neutron triple-axis spectrometer FLEXX at the BER-II reactor

k=(1,0,1)

Excitations from a Bose-Einstein Condensate of Magnons in Coupled Spin Ladders

is detected below

Quantitative Neutron Dark-field Imaging through Spin-Echo Interferometry.

\ensuremath{\sim}85\text{ }\text{K}

Neutron guide optimisation for a time-of-flight neutron imaging instrument at the European Spallation Source

. Our magnetic order-parameter measurements show that the ordered Fe moment along the

Investigating time-of-flight spin-echo modulation for small-angle neutron scattering through experiments and simulation

a

Quantum spin correlations through the superconducting-to-normal phase transition in electron-doped superconducting Pr0.88LaCe0.12CuO4-δ

axis reaches a maximum at

The upgraded cold neutron three-axis spectrometer FLEXX at BER II at HZB

\ensuremath{\sim}40\text{ }\text{K}

Neutron resonance spin-echo upgrade at the three-axis spectrometer FLEXX

, below which an anomalous expansion of the