Recent research on intrinsic magnetic topological insulators (MTIs), MnBi2Te4, sheds new light on the observation of a long-expected high-temperature quantum anomalous Hall effect (QAHE). However, the strong interlayered anti-ferromagnetic (AFM) coupling hinders the practical applications without applying a magnetic field. Thus, how to adjust the magnetism of this compound under zero field is essential. Here, we theoretically and experimentally study the magnetic properties of two new promising intrinsic MTI candidates MnBi4Te7 and MnBi6Te10, formed by intercalating the Bi2Te3 layer into MnBi2Te4. The first-principles calculations reveal that the relative energy between ferromagnetic (FM) and AFM states is greatly reduced by Bi2Te3 intercalations. The calculated energy barriers for the spin flipping process also point out that the metastable FM state is more easily retained by intercalation. Meanwhile, we also experimentally carry out magnetic and transport measurements on these materials. By increasing Bi2Te3 intercalations, the AFM coupling becomes weaker, and an almost fully polarized FM state can be preserved in MnBi6Te10 at low temperatures, which are consistent with our calculations. We believe that the demonstration of the intrinsic MTI preserving zero-field FM state and the in-depth investigation for the mechanism behind pave the way for investigating the high-temperature QAHE and the related physics.

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Large unsaturated magnetoresistance (XMR) with magnitude ∼10 3 % is observed in topological insulator candidate TaSe 3 from our high field (up to 38 T) measurements.Two oscillation modes are detected associated with the bulk pockets from our Shubnikov-de Hass (SdH) measurements, consistent with our first-principles calculations. However, our SdH measurements fails to determine the existence of topological surface states in TaSe 3 , calling for more powerful means to detect on this compound. Moreover, our two-band model analysis exhibits that an imperfect density ratio / ≈ 0.9 accounts for XMR at T< 20 K. At T> 20 K, a sudden change of density of carriers suggests a reconstruction of the Fermi surface. Thus, TaSe 3 may provide an opportunity to allow us to observe XMR in a topological insulator and to exploit the potential interplay between the XMR and topological surface states for the first time.