On the synthesis, characterization and magnetic properties of two new phases discovered in the PbO–Fe2O3–P2O5 system

• Three FM-like second order phase transitions in PbFe3O(PO4)3 powders.
• Critical exponents (β,γ,δ) in PbFe3O(PO4)3 consistent with mean-field behavior.
• Discovery of a new langbeinite phase, Pb1.5Fe2(PO4)3

The PbFe3O(PO4)3 powder compound was studied by means of X-ray diffraction (XRD) from 300 to 6 K, electron-probe microanalysis (EPMA) coupled with wavelength dispersion spectroscopy (WDS), calorimetric (DSC and specific heat) and magnetic properties measurements. Magnetization, magnetic susceptibility and specific heat measurements carried out on PbFe3O(PO4)3 powders firmly establish a series of three ferromagnetic (FM)-like second order phase transitions spanned over the 32–8 K temperature range. Discrepancies between magnetization and specific heat data obtained in PbFe3O(PO4)3 powders and single crystals are highlighted. A first extraction of the critical exponents (β,γ,δ) was performed by ac magnetic susceptibility in both PbFe3O(PO4)3 powders and single crystals and the values were found to be consistent with mean-field theory. Further exploration of the PbO–Fe2O3–P2O5 system led to the discovery of a new langbeinite phase, Pb1.5Fe2(PO4)3, the crystal structure of which was solved by room temperature single crystal XRD (P213, Z=4, a=9.7831(2) Å). This phase does not undergo any structural phase transition down to 6 K nor any kind of long range ordering down to 2 K.

Three ferromagnetic-like phase transitions discovered in the new compound PbFe3O(PO4)3 by specific heat and ZFC/FC magnetization measurements. Figure optionsDownload as PowerPoint slide