Antiferromagnetism in semiconductingSrMn2Sb2andBaMn2Sb2single crystals

Abstract

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 $\ensuremath{\rho}$, heat capacity ${C}_{\mathrm{p}}$, and magnetic susceptibility $\ensuremath{\chi}$ measurements versus temperature $T$, and magnetization versus field $M(H)$ 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 $\ensuremath{\rho}(T)$ data indicate semiconducting behaviors for both compounds with activation energies of $\ensuremath{\gtrsim}0.35$ eV for ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ and 0.16 eV for ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$. The $\ensuremath{\chi}(T)$ and ${C}_{\mathrm{p}}(T)$ 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 $\ensuremath{\chi}(T\ensuremath{\le}{T}_{\mathrm{N}})$ 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 $M(H)$ data for ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ exhibit a continuous metamagnetic transition at low fields $0<H\ensuremath{\lesssim}1$ T, whereas ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$ exhibits no metamagnetic transitions up to 5.5 T. The $\ensuremath{\chi}(T)$ and ${C}_{{}_{\mathrm{p}}}(T)$ 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.