Magnetovolume effects and thermal expansion anomalies during a phase transition in a chiral ferromagnet MnSi with topological features of the electronic structure

Within the framework of the theory of band magnetism and in the Heine model for the dependence of the electronic spectrum on volume, magnetovolume effects in the chiral quantum ferromagnet MnSi, with topological features of the electronic structure, are studied. New mechanisms of magnetovolume effects associated with the spin short-range order arising during a phase transition in fragments of right- and left-chiral spin helices with fixed Berry phases are considered. The calculated temperature dependences of the volumetric coefficient of thermal expansion (VTCE) describe the observed anomalies $\beta(T)$ and show that the disappearance of chiral spin charges associated with the Dzyaloshinsky–Moriya interaction is accompanied by a change in the sign of the VTCE. In this case, the fluctuation phase considered corresponds to that observed during small angle scattering of polarized neutrons.