Spin-phonon coupling in Mn1-xFexSi

We propose to investigate the coupling of lattice to spin degrees of freedom in the helimagnet MnSi and study the effect of Fe substitution in Mn1-xFexSi with x=0.09 and 0.14. Previously, we found magnetically induced renormalization of phonons in isostructural FeSi and preliminary data for MnSi encourage a detailed study – in particular with respect to the fascinating magnetic properties of the latter compound. The focus of the study will be on the momentum dependent phonon renormalization for which we need to investigate a significant part of reciprocal space with a particular focus on the 110-001 scattering plane since we found strongly increased phonon line widths in FeSi at Q=(2.5,2.5,2.5).The high sensitivity of magnetic phenomena to extrinsic parameters makes this compound series ideal to unravel and understand magnetism-induced phonon renormalization.