Heterometallic 3d-4f complexes as air-stable molecular pre-cursors in low temperature syntheses of stoichiometric rare-earth orthoferrite powders

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  • External authors:
  • Marwah M Alsowayigh
  • Grigore Timco
  • Ivana Borilovic
  • Abdulaziz Alanazi
  • Inigo Vitorica-Yrezabal
  • George Whitehead
  • Paul Mcnaughter
  • Paul O'Brien

Abstract

Four 3d-4f hetero-polymetallic complexes [Fe2Ln2((OCH2)3CR)2(O2CtBu)6(H2O)4] (where Ln = La (1 and 2) and Gd (3 and 4); and R = Me (1 and 3) and Et (2 and 4)) are synthesised and analysed using elemental analysis, Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and SQUID magnetometry. Crystal structures are obtained for both methyl derivatives and show that the complexes are isostructural and adopt a defective dicubane topology. The four heavy metals are connected with two alkoxide bridges. These four precursors are used as single-source precursors to prepare rare-earth orthoferrite pervoskites of the form LnFeO3. Thermal decomposition in a ceramic boat in a tube furnace gives orthorhombic LnFeO3 powders using optimised temperatures and decomposition times: LaFeO3 formed at 650 ℃ over 30 min, whereas GdFeO3 formed at 750 ℃ over 18 h. These materials are structurally characterised using powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray map spectros-copy, and SQUID magnetometry. EDX spectroscopy mapping reveals a homogenous spatial distribution of elements for all four materials consistent with LnFeO3. Magnetic measurements on complexes 1-4 confirms the presence of weak antiferro-magnetic coupling between the central Fe(III) ions of the clusters and negligible ferromagnetic interaction with peripheral Gd(III) ions in 3 and 4. Zero field cooled (ZFC) and field-cooled (FC) measurements of magnetization of LaFeO3 and GdFeO3 in the solid state suggests that both materials are ferromagnetic, and both materials show open magnetic hysteresis loops at 5 K and 300 K, with Msat higher than previously reported for these as nanomaterials. We conclude that this is a new and facile low temperature route to these important magnetic materials that is potentially universal limited only by what metals can be programmed into the precursor complexes.

Bibliographical metadata

Original languageEnglish
JournalInorganic Chemistry
Publication statusAccepted/In press - 17 Sep 2020