Physical Properties of $Ba_2 Mn_2 Sb_2 O$ Single Crystals
  We report both experimental and theoretical investigations of the physical properties of Ba$_\mathrm{2}$Mn$_\mathrm{2}$Sb$_\mathrm{2}$O single crystals. This material exhibits a hexagonal structure with lattice constants: a = 4.7029(15) \AA{} and c = 19.9401(27) \AA{}, as obtained from powder X-ray diffraction measurements, and in agreement with structural optimization through density functional theory (DFT) calculations. The magnetic susceptibility and specific heat show anomalies at T$_\mathrm{N}$ = 60 K, consistent with antiferromagnetic ordering. However, the magnitude of T$_\mathrm{N}$ is significantly smaller than the Curie-Weiss temperature ($\mid$$\mathrm{\Theta_{CW}}$$\mid$ $\approx$ 560 K), suggesting a magnetic system of reduced dimensionality. The temperature dependence of both the in-plane and out-of-plane resistivity changes from an activated at $T$ $>$ T$_\mathrm{x}$ $\sim$ 200 K to a logarithmic at $T$ $<$ T$_\mathrm{x}$. Correspondingly, the magnetic susceptibility displays a bump at T$_\mathrm{x}$. DFT calculations at the DFT + U level support the experimental observation of an antiferromagnetic ground state. 
J. Li, C. E. Ekuma, I. Vekhter, M. Jarrell, J. Moreno, S. Stadler, A.   B. Karki, and R. Jin
cond-mat.str-el cond-mat.supr-con