Lattice Dynamics and Enhanced Electron-Phonon Coupling of Itinerant Magnet Fe1-xCoxSi (x ≥ 0.3): A 57fe Mössbauer Spectroscopy Study

The magnetic phase transition in itinerant magnets involves many fundamental physical problems. Here we report a systematic investigation on the Fe-57 M & ouml;ssbauer spectroscopy of B20-type Fe1-xCoxSi (0.3 <= x <= 0.8) compounds in combination with macroscopic magnetism and resistance measurements. We observed non-Fermi liquid behavior at low temperatures in the region of phase transition (close to x = 0.7), as well as significant phonon softening. In addition, with the increase of Co content, the effect of electron-phonon coupling on the hyperfine field is gradually comparable to that of spin fluctuations. Our observations indicate that electron doping promotes electron-electron correlations and facilitates electron-phonon interactions at the cost of suppression of magnetic ordering and magnetic fluctuations, suggesting that interactions between phonons and other quasiparticles play a crucial role in the magnetic phase transitions of itinerant helical magnets.