Pure iron manganite FeMn2O4 was prepared at 1250°C and quenched. It crystallizes in the b.c. tetragonal system D 4h19. Neutron diffraction measurements above the Curie temperature (120°C) show that the inversion parameter is 0.91 (nearly inverse spinel). The spontaneous magnetization at 4.2°K measured in high static and pulsed fields is 1.55 μB/mol. The magnetic moment was observed to increase linearly above 70 kOe and showed the presence of a strong anisotropy with easy axis near the [101] direction (unusual fact). Neutron diffraction measurements at 4.2°K lead to the determination of the magnetic structure of FeMn2O4. The tetrahedral sublattice moments (4.3 μB) are collinear in a (010) plane making an angle of - 172° with Ox [100]. Spins in octahedral sites (3.1 μB) are divided into four magnetic sublattices with a pyramidal arrangement whose axis of symmetry lies in the plane (010) and makes an angle of 14° with Ox [100]. At 55°K the spins of the octahedral sublattices become collinear, the easy magnetization direction remaining unchanged up to 310°K where it changes to the [110] direction, the magnetic structure of FeMn2O4 becoming completely collinear. © 1969 The American Institute of Physics.
