Magnetism of Tetragonal β-Fe3Se4 Nanoplates Controllably Synthesized by Thermal Decomposition of (β-Fe2Se3)4[Fe(tepa)] Hybrid

Abstract

We report magnetism of tetragonal β-Fe3Se4 nanoplates controllably synthesized by thermal decomposition at 603 K of inorganic–organic (β-Fe2Se3)4[Fe(tepa)] hybrid nanoplates (tepa = tetraethylenepentamine). (β-Fe2Se3)4[Fe(tepa)] hybrid precursor and β-Fe3Se4 nanoplates are in single crystal features as characterized by selected area electron diffraction. Rietveld refinements reveal that ordered inorganic–organic (β-Fe2Se3)4[Fe(tepa)] hybrid nanoplates are in a tetragonal layered crystal structure with a space group of I4cm (108) and room-temperature lattice parameters are a = 8.642(0) Å and c = 19.40(3) Å, while the as-synthetic tetragonal β-Fe3Se4 nanoplates have a layered crystal structure with the P4/nmm space group, and room-temperature lattice parameters are a = 3.775(8) Å and c = 5.514(5) Å. Magnetic measurements show the weak ferrimagnetism for (β-Fe2Se3)4[Fe(tepa)] hybrid nanoplates at room temperature, while the as-synthetic β-Fe3Se4 nanoplates are antiferromagnetic in a temperature range between 120 and 420 K but in a ferrimagnetic feature below ~120 K. The as-synthetic β-Fe3Se4 nanoplates are thermally instable, which are transformed to ferrimagnetic β-Fe3Se4 nanoplates by annealing at 623 K (a little higher than the synthetic temperature). There is an irreversible change from antiferromagnetism of the as-synthetic β-Fe3Se4 phase to the ferrimagnetism of the as-annealed β-Fe3Se4 phase in a temperature between 420 and 470 K. Above 470 K, the tetragonal β-Fe3Se4 phase transforms to monoclinic Fe3Se4 phase with a Curie temperature (TC) of ~330 K. This discovery highlights that crystal structure and magnetism of Fe-Se binary compounds are highly dependent on both their phase compositions and synthesis procedures.