NEUTRON-DIFFRACTION STUDY OF MAGNETIC ORDERING IN CA2MNO4

Ca2MnO4 shows anomalous magnetic-susceptibility behavior rather similar to that of the isostructural fluoride K2NiF4, in which the existence of long-range two-dimensional character has recently been clearly demonstrated. A powder-diffraction study of Ca2MnO4 with 2.5 neutrons has revealed that three-dimensional ordering sets in at about 114°K with an antiferromagnetic structure different from that of K2NiF4. The antiferromagnetic basal-plane arrangement of the latter is retained, but the layers are stacked in such a way that adjacent c-axis moments 12 apart are coupled antiparallel instead of parallel, and the magnetic unit cell is double the chemical cell in this direction. The moments are directed along [001] and their magnitude is 2.0μB per Mn4+ ion, significantly less than the spin-only value of 3μB. Above 114°K, there are indications of two-dimensional effects, but these are not so pronounced as in K2NiF4. © 1969 The American Physical Society.