Ferromagnetism in van der Waals compound Mn(Sb, Bi)₂Te₄

The prospect of realizing the quantum anomalous Hall effect at elevated temperatures has inspired many recent explorations of magnetic van der Waals compounds with the composition of MnBi₂Te₄, MnBi_2nTe_3n+1 and their Sb-substituted alloys such as Mn(Sb, Bi)₂Te₄. While most single crystals synthesized to date exhibit a type-A antiferromagnetic ground state, we show that under certain synthetic conditions, Sb-rich compound MnSb_1.8Bi_0.2 Te₄ can form a net ferromagnetic state with a Curie temperature of 26 K. We report on the structural, magnetic, and electrical properties of MnSb_1.8Bi_0.2 Te₄ combining magneto-transport, SQUID magnetometry, x-ray and neutron scattering techniques. We show that the low-field slope of the Hall signal serves as a good proxy for the magnetic susceptibility in microscopic samples. Mn-Sb site mixing may play a key role in mediating the observed ferro (ferri)magnetism. Excess anomalous Hall effect similar to topological Hall effect reported in other materials onsets at T ~ 10 K and together with other probes, suggests possible new magnetic ground states.
[1] Yangyang Chen et al, “Ferromagnetism in van der Waals compound MnSb_1.8Bi_0.2Te₄”, Phys. Rev. Mat. 4, 064411 (2020)
In collaboration with Y. Chen, Y-W. Chuang, S. H. Lee, Y. Zhu, K. Honz, Y. Guan, Y. Wang, K. Wang, Z. Mao, C. Heikes, P. Quarterman, P. Zajdel, J. A. Borchers, and W. Ratcliff II