Carrier tuned magnetism in topological insulator Mn:Bi₂Te₃

Here we report a study of Mn-doped Bi₂Te₃ where we found magnetism and Anomalous Hall Effect (AHE) strongly dependent on conduction type. In n-type Mn:Bi₂Te₃, we observe a pronounced AHE proportional to magnetization M arising from magnetic moments of Mn ions, measured independently using Hall sensor arrays. In p-type, while direct M measurements show the system to be weakly ferromagnetic and AHE is NOT observed. In our experiment we lower electron density using high energy (~2.5 MeV) electron beams. We find that for n-type, AHE decreases with decreasing electron density. By way of contrast, in p-type crystals the irradiation produces conversion from p- to n-type and no AHE is observed. Our DFT calculations show that the magnetic moment on the Mn atom increases from n- to p-doping in the intercalated and interstitial cases; the opposite is true in the substitutional case. We demonstrate how AHE can be tuned by changing carrier density either by anneals or electrostatic gating. We discuss how this system with band inversion differs from trivial dilute magnetic semiconductors where moments couple via itinerant hole carriers by RKKY interaction.