Two-dimensional measurements of magnons

Magnon scattering in MnF2 has been recorded in a complete reciprocal plane and not only in the main symmetry directions. This has been done effectively with the Flat-cone spectrometer E2 at the Hahn-Meitner-Institut using a multidetector with the option of energy analysis in a large and continuous angular range. In integral measurements (without energy analysis), magnon scattering is observed with high intensity in the form of two butterfly wings around the magnetic Bragg reflections. The distance between the wings is a measure of the anisotropy gap energy at the zone center. From the intensity distribution, we derived exchange interaction parameters and the dipolar energy, in good agreement with the results from the triple axis measurements.