Antiferromagnetism in CaAl$_2$Si$_2$-type CaMn$_2$As$_2$ and SrMn$_2$As$_2$ single crystals$^{\ast}$

Magnetic susceptibility versus temperature $\chi(T)$ measurements of $\rm{CaMn_2As_2}$ and $\rm{SrMn_2As_2}$ crystals show clear antiferromagnetic (AFM) transitions at $T_{\rm{N}}\approx 65$ K and 120 K,$^{1}$ respectively. The anisotropic behaviors in $\chi(T\leq T_{\rm{N}})$ suggest that both compounds are noncollinear antiferromagnets which may result either from an intrinsic noncollinear structure or from multiple collinear AFM domains that are not aligned collinearly.$^{2}$ The $\chi(T)$ data at $T>T_{\rm{N}}$ reveal that both compounds exhibit strong short-range AFM ordering, evidently associated with quasi-two-dimensional spin lattices. The electrical resistivities show insulating ground states with activation energies of $\approx 63$ meV in $\rm{CaMn_2As_2}$ and 44 meV in $\rm{SrMn_2As_2}$. The experimental results thus reveal that both $\rm{(Ca,Sr)Mn_2As_2}$ materials are AFM insulators at low temperatures and in analogy with the high $T_{\rm{c}}$ cuprates, may be potential parent compounds for CaAl$_2$Si$_2$-type superconductors.$\\^{\ast}$Work was supported by the USDOE under Contract No. DE-AC02-07CH11358.$\\^{1}$Z.W. Wang et. al, J. Phys. Chem. Solids $\mathbf{72}$, 457 (2011).\\$^{2}$D. C. Johnston, PRL \textbf{109}, 077201 (2012); PRB \textbf{91}, 064427 (2015).