Temperature-dependent evolution of micromagnetic structure of B20-type Fe1-xCoxGe studied by Mössbauer spectroscopy

The non-collinear magnetic structures hosted in magnets with broken central inversion symmetry, some of which are topologically non-trivial, have unique physical properties and application prospects. This paper presents a detailed study of the temperature evolution of the micromagnetic structures of B20-type Fe _1-xCo _xGe (x = 0, 0.05, 0.10) polycrystalline samples using ⁵⁷Fe Mössbauer spectroscopy. We take the relatively weak electric quadrupole interaction as a perturbation of the hyperfine magnetic interaction to obtain the distribution of the hyperfine magnetic field H _hf (φ) in the plane perpendicular to the magnetic propagation vector k _s. It is found that the geometric features of H _hf (φ) are sensitive to the relative orientation of k _s regarding the electric field gradient at the iron nucleus, as well as to the spin texture. The temperature dependence of H _hf (φ) provides a distinct signal of first-order phase transition when k _s shifts from [1 0 0] to [1 1 1]. The doping of cobalt atoms leads to out-of-plane component and in-plane component aggregation of the neighboring iron magnetic moments. These results are instructive for understanding the dynamical behavior of spiral magnets with long-periods.