Magnetic interactions of 4f electrons in the topological insulator chalcogenide Bi2Se3

Here, the gap opening mechanism of a topological insulator, the quantum anomalous Hall effect and the axion physics are still pressing open questions and a microscopic viewpoint to further understand the role of magnetism in topology is highly desirable. In this work we have performed a micro scopic investigation, by means of electron spin resonance (ESR) along with complementary bulk measurements, on the chalcogenide (Bi1-xGdx)2Se3 (x = 0, 0.001, 0.002 and 0.006). Our analysis of the Gd3+ spin dynamics reveal no significant change of the Fermi surface as a function of Gd3+ concentration, which indicates that the 4f magnetism is different from the non-local effects induced by transition metals (d electrons) substitutions. Additionally, we observe an unusual evolution of the Gd3+ ESR spectra as a function of the applied magnetic field, which we discuss considering the magnetic interaction between Gd3+ 4f electrons and impurity centers such as Se vacancies. This interaction would give rise to a local weak antilocalization effect surrounding the Gd3+ ions. Such mechanism is observable due to particular details of the Gd3+ 4f electrons magnetism in this system compared to d electrons. Our work points out that rare earth substitutions in this model topological insulator is a promising path to explore the axion insulating systems.