A-type antiferromagnetic order in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>MnBi</mml:mi><mml:mn>4</mml:mn></mml:msub><mml:msub><mml:mi>Te</mml:mi><mml:mn>7</mml:mn></mml:msub></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>MnBi</mml:mi><mml:mn>6</mml:mn></mml:msub><mml:msub><mml:mi>Te</mml:mi><mml:mn>10</mml:mn></mml:msub></mml:mrow></mml:math> single crystals
J.-Q. Yan, Y. H. Liu, D. S. Parker, Y. Wu, A. A. Aczel, M. Matsuda, M. A. McGuire, B. C. Sales
Abstract
${\mathrm{MnBi}}_{4}{\mathrm{Te}}_{7}$ and ${\mathrm{MnBi}}_{6}{\mathrm{Te}}_{10}$ are two members with $n=2$ and 3 in the family of ${\mathrm{MnBi}}_{2n}{\mathrm{Te}}_{3n+1}$ where the $n=1$ member, ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$, has been intensively investigated as the first intrinsic antiferromagnetic topological insulator. Here we report the A-type antiferromagnetic order in these two compounds by measuring magnetic properties, electrical and thermal transport, specific heat, and single-crystal neutron diffraction. Both compounds order into an A-type antiferromagnetic structure as does ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ with ferromagnetic planes coupled antiferromagnetically along the crystallographic $c$ axis. While no evidence for any in-plane ordered moment is found for ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ or ${\mathrm{MnBi}}_{6}{\mathrm{Te}}_{10}$, weak reflections at half-$L$ positions along the [0 0 $L]$ direction are observed for ${\mathrm{MnBi}}_{4}{\mathrm{Te}}_{7}$ suggesting an in-plane ordered moment around $0.15{\ensuremath{\mu}}_{B}/\mathrm{Mn}$. The ordering temperature, ${T}_{N}$, is 13 K for ${\mathrm{MnBi}}_{4}{\mathrm{Te}}_{7}$ and 11 K for ${\mathrm{MnBi}}_{6}{\mathrm{Te}}_{10}$. The magnetic order is also manifested in the anisotropic magnetic properties. For both compounds, the interlayer coupling is weak and a spin-flip transition occurs when a magnetic field of around 1.6 kOe is applied along the $c$ axis at 2 K. As observed in ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$, when cooling across ${T}_{N}$, no anomaly was observed in the temperature dependence of thermopower. On the other hand, critical scattering effects are observed in thermal conductivity although the effect is less pronounced than that in ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$.