Ferrimagnetism and spin reorientation in the high-pressure double double perovskites CaMnCrSbO6 and CaMnFeSbO6

Two $\mathrm{CaMn}B\mathrm{Sb}{\mathrm{O}}_{6}$ ($B=\mathrm{Cr}$ and Fe) high-pressure double double perovskites are reported. Spins in $\mathrm{Ca}\mathrm{Mn}\mathrm{Cr}\mathrm{Sb}{\mathrm{O}}_{6}$ order below ${T}_{\mathrm{C}}=49\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ into a collinear ferrimagnetic arrangement with spins in the $xy$ plane. $\mathrm{Ca}\mathrm{Mn}\mathrm{Fe}\mathrm{Sb}{\mathrm{O}}_{6}$ has the same ordered magnetic structure below ${T}_{\mathrm{C}1}=55$ K, but also shows a second magnetic transition at ${T}_{\mathrm{C}2}=21\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ where the spins reorient towards the $z$ axis. This may reflect a greater degree of magnetic disorder for $B=\mathrm{Fe}$ and A-B intersite charge transfer may also be significant.