Strongly anisotropic spin dynamics in magnetic topological insulators

The recent discovery of magnetic topological insulators has opened new avenues to explore exotic states matter that can emerge from the interplay between electronic and degrees freedom, be it ordered or strongly fluctuating. Motivated by effects dynamics moments have on surface states, we investigate fluctuations across $({\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}){({\mathrm{Bi}}_{2}{\mathrm{Te}}_{3})}_{\mathrm{n}}$ family. Our paramagnetic electron spin resonance experiments reveal contrasting Mn in different compounds, which manifests a anisotropic relaxation ${\mathrm{MnBi}}_{\text{2}}{\mathrm{Te}}_{\text{4}}$ while being almost isotropic ${\mathrm{MnBi}}_{\text{4}}{\mathrm{Te}}_{\text{7}}$. density-functional calculations explain these striking observations terms sensitivity local structure orientation, indicate anisotropy controlled carrier density, may directly affect states.