The Mn(II) phases LaSrMnO3.5 and LaBaMnO3.5 have been prepared by the topotactic reduction of LaSrMnO4 and LaBaMnO4 respectively. Preliminary neutron diffraction data show that LaSrMnO4 is antiferromagnetically ordered at 300K. Magnetisation data suggest the magnetic ordering temperature may be as high as 770K. Such a high ordering 3D magnetic ordering temperature in a layered phase would be unprecedented. We proposed to collect neutron powder diffraction data as a function of temperature to unambiguously characterise the magnetic behaviour of LaSrMnO3.5 and LaBaMnO3.5