Hydrothermal synthesis and magnetic properties of Fe3+-doped multiferroic hexagonal rare-earth manganates

Hexagonal RMn1−xFexO3 (R = Er, Tm, Yb and Lu; x = 0, 0.1, 0.3 and 0.5) were successfully synthesized via the low-temperature hydrothermal technique. Fe3+ doping was used to elevate the low antiferromagnetic transition temperature TN which is a fatal weakness for hexagonal manganates RMnO3 to be used as multiferroic materials. The structures, compositions, morphologies and magnetic properties of the samples and the valences of Mn and Fe were studied via the methods of XRD, Rietveld refinement, ICP-MS, EDS, SEM, SQUID and XPS. ErMnO3 and RMn1−xFexO3 (R = Tm, Yb and Lu; x = 0, 0.1, 0.3 and 0.5) were all of pure hexagonal structure while ErMn1−xFexO3 (x = 0.1, 0.3 and 0.5) comprised hexagonal and orthorhombic structures. As for the undoped RMnO3 (R = Er, Tm, Yb and Lu), the cell parameters a, c and cell volume V decreased while the antiferromagnetic transition temperatures TN rose with the decrease of R3+ radius. The antiferromagnetic transition temperatures TN were elevated by Fe3+ doping and a linear relation was observed between ΔTN and Fe doping concentration x. A percentage of Fe3+ doping elevated TN by 0.3-0.5 K, and the elevation was more obvious when the R3+ ionic radius was smaller.