A Study of the Magnetic Structure of LaMn 2 O 5 from Neutron Powder Diffraction Data

Polycrystalline LaMn 2 O 5 has been studied by neutron powder diffraction in conjunction with magnetization data. The crystal structure of this oxide contains infinite chains of edge‐sharing Mn 4+ O 6 octahedra, interconnected by Mn 3+ O 5 pyramids and LaO 8 units. Susceptibility measurements show that LaMn 2 O 5 presents an antiferromagnetic order below a T N value of about 31 K. Neutron diffraction experiments confirm the long‐range ordering below this temperature in a magnetic structure characterized by the propagation vector k = (0,0,1/2). The magnetic arrangement is defined by the basis vectors ( G x , A y ,0) and (0,0, C ′ z ) for the Mn 4+ and Mn 3+ ions, respectively. At 3.5 K, the magnetic moments are 2.59(4) and 1.61(7) μ B for the Mn 3+ (4h site) and Mn 4+ ions (4f site), respectively. Superexchange interactions between the Mn 4+ ions through Mn 4+ –O–Mn 4+ paths are considered in order to explain the commensurate character of the magnetic structure in comparison with the incommensurate structures observed for most of the RMn 2 O 5 (R = rare earth metal) compounds. A spin‐glass‐type behaviour, which probably involves the short‐range order in the Mn 3+ sublattice, is observed above T N . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)