Probing of order parameters in magnetoelectric multiferroics by neutron diffraction

Neutron scattering methods are indispensable in studying structure-property relationships. Determination of spin arrangements in magnetically ordered materials makes neutron diffraction among the major tools in the research on multiferroics because to understand why a given compound displays or does not display the expected properties calls for detailed information on microscopic level. We describe the efforts to identify new candidate magnetoelectric materials based primarily on considerations of symmetry and the knowledge of the magnetic structure. We found that substitution of half manganese with iron introduces a low level of disorder between the two transition metal positions in the RFeMnO₅ (R=Tb,Yb) structure. The lack of evidence for a crystallographic phase transition to a polar space group rules out expectations of a spontaneous electric polarization. In addition, the observed collinear magnetic structure with k = 0 does not permit a spin polarization.. Therefore, by contrast to well known multiferroics RMn₂O₅ (R=Tb,Yb), YbMnFeO₅ and TbMnFeO₅ is not expected to be multiferroic compounds. Other examples in this article include nanosize powder material from the mixed oxide system YFe_xCr_1-xO₃ and Y-type hexaferrite multiferroic Ba₂Mg₂Fe₁₂O₂₂ as well as antiferromagnetic La_0.5Pb_0.5FeO₃.