Phase transitions in chiral ferromagnets with topological features of electronic structure (on the example of MnSi)

Abstract

Magnetic and topological electronic (TEP) phase transitions in chiral ferromagnets with the Dzyaloshinskii-Moriya (DM) interaction are considered. We consider the example of a chiral helical ferromagnet MnSi with a large Berry curvature of the Fermi surface. It is shown that the state of the spin subsystem with a ferromagnetic short-range order and with Berry phases arises as a result of a first-order transition from a helicoidal ferromagnetic phase with increasing temperature. This state is characterized by left-handed vortex microstructures and manifests itself through the topological Hall effect. In the region of the paramagnetic short-range order, vortex microstructures of both signs of spin chirality arise, which leads to the experimentally observed pattern of partial chirality. With an increase in temperature, TEP appears in the chiral paramagnetic state due to that the chemical potential leaves the region of the electronic spectrum with Berry curvature. As a result, the local magnetization and chiral interaction of the DM disappear. A quantitative agreement has been obtained between the calculations of the temperature dependence of the spin magnetic susceptibility and experimental data.