Magnetically doped topological materials tuned by electron irradiation

We have recently demonstrated that irradiation of topological materials, such as Bi$_2$Te$_3$ and Ca:Bi$_2$Se$_3$, with high energy (2.5 MeV) electron beams can sweep Fermi level E$_F$ across the bulk gap to charge neutrality point (CNP) [1]. Here we show that such irradiation technique applied to magnetically doped topological insulators (TIs) can be used to tune anomalous Hall effect (AHE). We performed irradiation experiments on a series of Mn-doped Bi$_2$Te$_3$ crystals, (Bi$_{1_x}$Mn$_x$)$_2$Te$_3$, using both \textit{p}- and \textit{n}-type starting materials. All materials, displayed magnetic hysteresis loops consistent with ferromagnetic order present. However, in transport the two conductivity types were found to be surprisingly different. While the \textit{p}-type crystals did convert to \textit{n}-type across CNP, no trace of AHE was detected. In contrast, \textit{n}-type materials showed pronounced hysteretic anomalous Hall resistance, consistent with magnetization. In the latter case, charge density has decreased and the zero-field Hall signal increased after irradiation. We will discuss how AHE in irradiated magnetically doped TIs can be fine tuned by electrostatic gating in the vicinity of CNP. [1]L. Zhao \textit{et al}, \textit{Nat. Comm.} \textbf{7}, 10957 (2016)