Lattice dynamics and enhanced electron–phonon coupling of itinerant magnet Fe1-Co Si (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 ⁵⁷Fe Mössbauer spectroscopy of B20-type Fe _{1- x}Co _xSi (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.