Fluctuation-Driven First-Order Transition in the Chiral Magnet MnSi
Pascal Krautscheid (Bonn)

The chiral magnet MnSi orders below T_C=29K. Measurements of the specific heat for various magnetic fields show a characteristic crossing point at T*=31K. Recent publications claimed that within the temperature range from T_C to T* topological excitations emerge and form an intermediate phase. I consider a coarse-grained Hamiltonian of MnSi and investigate the influence of chiral fluctuations on a second order mean-field transition. A self-consistent scheme to describe the behavior of the isotropic part of the Hamiltonian near the transition is used. Due to the coupling, chiral-fluctuations become critical on a sphere in momentum space and induce the experimentally observed first-order transitions. Without using a topoligical structure, the theory describes the crossing of the specific heat curves as well as further observed features.