Crystals of ${\mathrm{SrMn}}_2{\mathrm{Sb}}_2$ and ${\mathrm{BaMn}}_2{\mathrm{Sb}}_2$ were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity $\rho$, heat capacity $C_{\mathrm{p}}$, and magnetic susceptibility $\chi$ measurements versus temperature $T$, and magnetization versus field $M\left(H\right)$ isotherm measurements. ${\mathrm{SrMn}}_2{\mathrm{Sb}}_2$ adopts the trigonal ${\mathrm{CaAl}}_2{\mathrm{Si}}_2$-type structure, whereas ${\mathrm{BaMn}}_2{\mathrm{Sb}}_2$ crystallizes in the tetragonal ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$-type structure. The $\rho \left(T\right)$ data indicate semiconducting behaviors for both compounds with activation energies of $\gtrsim 0.35$ eV for ${\mathrm{SrMn}}_2{\mathrm{Sb}}_2$ and 0.16 eV for ${\mathrm{BaMn}}_2{\mathrm{Sb}}_2$. The $\chi \left(T\right)$ and $C_{\mathrm{p}}\left(T\right)$ data reveal antiferromagnetic (AFM) ordering at $T_{\mathrm{N}}$ = 110 K for ${\mathrm{SrMn}}_2{\mathrm{Sb}}_2$ and 450 K for ${\mathrm{BaMn}}_2{\mathrm{Sb}}_2$. The anisotropic $\chi (T\le T_{\mathrm{N}})$ data also show that the ordered moments in ${\mathrm{SrMn}}_2{\mathrm{Sb}}_2$ are aligned in the hexagonal $ab$ plane, whereas the ordered moments in ${\mathrm{BaMn}}_2{\mathrm{Sb}}_2$ are aligned collinearly along the tetragonal $c$ axis. The $ab$-plane $M\left(H\right)$ data for ${\mathrm{SrMn}}_2{\mathrm{Sb}}_2$ exhibit a continuous metamagnetic transition at low fields $0<H\lesssim 1$ T, whereas ${\mathrm{BaMn}}_2{\mathrm{Sb}}_2$ exhibits no metamagnetic transitions up to 5.5 T. The $\chi \left(T\right)$ and $C_{{}_{\mathrm{p}}}\left(T\right)$ data for both ${\mathrm{SrMn}}_2{\mathrm{Sb}}_2$ and ${\mathrm{BaMn}}_2{\mathrm{Sb}}_2$ indicate strong dynamic short-range AFM correlations above their respective $T_{\mathrm{N}}$ up to at least 900 K within a local-moment picture, corresponding to quasi-two-dimensional magnetic behavior. The present results and a survey of the literature for Mn pnictides with the ${\mathrm{CaAl}}_2{\mathrm{Si}}_2$ and ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$ crystal structures show that the $T_{\mathrm{N}}$ values for the ${\mathrm{CaAl}}_2{\mathrm{Si}}_2$-type compounds are much smaller than those for the ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$-type materials.

• Received 16 October 2017

DOI:https://doi.org/10.1103/PhysRevB.97.014402