The aim of the proposed experiment is to determine the temperature dependence of the ordered magnetic structures of LaMnSbO and NdMnSbO. These oxy-antimonides are related to the iron based high-temperature superconductors, and of possible interest as magnetoresistance and high-temperature thermoelectric materials. Magnetic susceptiblity measurements on NdMnSbO evidence two transitions below room temperature, while the Mn ordering temperature in both materials appears to lie above RT. Neutrons are needed to fully characterise the magnetic ordering in these materials.