Ferromagnetic MnBi4Te7 obtained with low concentration Sb doping: A promising platform for exploring topological quantum states

The tuning of magnetic phase, chemical potential, and structure is crucial to observe diverse exotic topological quantum states in MnBi 2 Te 4 (Bi 2 Te 3 ) m ( m = 0, 1, 2, & 3). Here we show a ferromagnetic (FM) phase with a chiral crystal structure in Mn(Bi 1 -x Sb x ) 4 Te 7 , obtained via tuning the growth conditions and Sb concentration. Unlike previously reported Mn(Bi 1 x Sb x ) 4 Te 7, which exhibits FM transitions only at high Sb doping levels, our samples show FM transitions ( T C = 13.5 K) at 15%-27% doping levels. Furthermore, our single crystal x-ray diffraction structure refinements find Sb doping leads to a chiral structure with the space group P3 contrasted with the centrosymmetric P 3̅ m 1 crystal structure of the parent compound MnBi 4 Te 7 . Through ARPES measurements, we also demonstrated that the non-trivial band topology is preserved in the Sb-doped FM samples. Given that the non-trivial band topology of this system remains robust for low Sb doping levels, our success in making FM Mn(Bi 1 x Sb x ) 4 Te 7 with x = 0.15, 0.175, 0.2 & 0.27 paves the way for realizing the predicted topological quantum states such as axion insulator and Weyl semimetals. Additionally, we also observed magnetic glassy behavior in both antiferromagnetic MnBi 4 Te 7 and FM Mn(Bi 1 -x Sb x ) 4 Te 7 samples, which we believe originates from cluster spin glass phases coexisting with long-range AFM/FM orders. We have also discussed how the antisite Mn ions impact the interlayer magnetic coupling and how FM interlayer coupling is stabilized in this system.