Crystal growth and magnetic structure of MnBi 2 Te 4

Millimeter-sized ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ single crystals are grown out of a Bi-Te flux and characterized using magnetic, transport, scanning tunneling microscopy, and spectroscopy measurements. The magnetic structure of ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ below ${T}_{N}$ is determined by powder and single-crystal neutron diffraction measurements. Below ${T}_{N}$ = 24 K, ${\mathrm{Mn}}^{2+}$ moments order ferromagnetically in the $ab$ plane but antiferromagnetically along the crystallographic $c$ axis. The ordered moment is 4.04(13)${\ensuremath{\mu}}_{B}$/Mn at 10 K and aligned along the crystallographic $c$ axis in an A-type antiferromagnetic order. Below ${T}_{N}$, the electrical resistivity drops upon cooling or when going across the metamagnetic transition in increasing magnetic fields. A critical scattering effect is observed in the vicinity of ${T}_{N}$ in the temperature dependence of thermal conductivity, indicating strong spin-lattice coupling in this compound. However, no anomaly is observed in the temperature dependence of thermopower around ${T}_{N}$. Fine tuning of the magnetism and/or electronic band structure is needed for the proposed topological properties of this compound. The growth protocol reported in this work might be applied to grow high-quality crystals where the electronic band structure and magnetism can be finely tuned by chemical substitutions.