Phase transitions in chiral ferromagnets with topological features of electronic structure.

What is it about?

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 microstructure 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.

Featured Image

Why is it important?

Thus, we obtain that near the ground state there is an energy gap between the chemical potential and the Berry curvature region of the electronic structure. Therefore, in helicoidal ferromagnets with broken inverse symmetry of the crystal lattice (for example, B20), an equilibrium region of chiral long-range order with spin helices arises. At a temperature TC, the chemical potential is in the Berry curvature region and the negative intermode coupling defined by curvature DOS is realized.

Perspectives