Local spin-flip transitions induced by magnetic quantum impurities in two-dimensional magnets

We predict a general local spin-flip transition mechanism caused by magnetic quantum impurities in (partially) polarized phases of quantum magnets in the absence of conservation laws. This transition arises when a magnon bound-state crosses zero energy as a function of the magnetic field. As an application, we study two-dimensional (2D) van der Waals magnets described by the Kitaev-Heisenberg honeycomb model which applies to the transition metal trihalides ${\mathrm{CrI}}₃$ and $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}₃$. We consider the adatom and substitutional impurity positions, and show how spin-flip transitions can be detected in scanning tunneling spectroscopy.