Coupled quasimonopoles in chiral magnets

Magnetic singularities, also known as magnetic monopoles or Bloch points, represent intriguing phenomena in nanomagnetism. We show that a pair of coupled Bloch points- A dipole string-may appear as a stable state in cubic chiral magnets. Analysis of the thermodynamic stability of such objects in the interior of crystals and in geometrically confined systems is presented. Employing advanced Monte Carlo simulations, we reveal an effect of spontaneous nucleation of dipole strings with characteristic size on the order of the helix pitch at temperature close to the paramagnetic phase transition. Such behavior of chiral magnets at elevated temperature drastically distinguishes them from ordinary ferromagnets and may provide a significant contribution to the topological Hall effect even in the absence of skyrmions. © 2020 American Physical Society.