Ames Laboratory; Physics and Astronomy
Physics and Astronomy, Ames Laboratory
Physical Review B
Crystals of SrMn 2 Sb 2 and BaMn 2 Sb 2 were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity ρ , heat capacity C p , and magnetic susceptibility χ measurements versus temperature T , and magnetization versus field M ( H ) isotherm measurements. SrMn 2 Sb 2 adopts the trigonal CaAl 2 Si 2 -type structure, whereas BaMn 2 Sb 2 crystallizes in the tetragonal ThCr 2 Si 2 -type structure. The ρ ( T ) data indicate semiconducting behaviors for both compounds with activation energies of ≳ 0.35 eV for SrMn 2 Sb 2 and 0.16 eV for BaMn 2 Sb 2 . The χ ( T ) and C p ( T ) data reveal antiferromagnetic (AFM) ordering at T N = 110 K for SrMn 2 Sb 2 and 450 K for BaMn 2 Sb 2 . The anisotropic χ ( T ≤ T N ) data also show that the ordered moments in SrMn 2 Sb 2 are aligned in the hexagonal a b plane, whereas the ordered moments in BaMn 2 Sb 2 are aligned collinearly along the tetragonal c axis. The a b -plane M ( H ) data for SrMn 2 Sb 2 exhibit a continuous metamagnetic transition at low fields 0 < H ≲ 1 T, whereas BaMn 2 Sb 2 exhibits no metamagnetic transitions up to 5.5 T. The χ ( T ) and C p ( T ) data for both SrMn 2 Sb 2 and BaMn 2 Sb 2 indicate strong dynamic short-range AFM correlations above their respective T 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 CaAl 2 Si 2 and ThCr 2 Si 2 crystal structures show that the T N values for the CaAl 2 Si 2 -type compounds are much smaller than those for the ThCr 2 Si 2 -type materials.
Department of Energy Subject Categories
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
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