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.
Highlights
The synthesis and characterization of iron selenides are interesting topics in materials sciences, due to their outstanding electrical and magnetic properties, which are sensitively dependent on their phase compositions and crystal structures [1,2,3,4]
The band of 1613 cm−1 in the hybrid nanoplates is attributed to the bending vibrations of N−H in tepa, which is larger than the value (1591 cm−1) for raw tepa solvent, indicating the complexation of tepa with iron ions and the elongation of N−H bonds
Thermal gravimetric analysis (TGA) curve in Figure 3a shows a small weight loss (~2.8 wt%) from room temperature to ~570 K due to a small amount of free tepa and other organic solvents absorbed on the surface of the hybrid nanoplates, and a sharp weight loss (13.1 wt%) between the onset temperature (Tonset) of ~570 K and the end temperature (Tend) of 726 K for decomposition, ature to ~570 K due to a small amount of free tepa and other organic solvents absorbed on the surface of the hybrid nanoplates, and a sharp weight loss (13.1 wt%) between the onset temperature (Tonset) of ~570 K and the end temperature (Tend) of 726 K for decomposition, due to the loss of the bonded tepa and a small amount of Se
Summary
The synthesis and characterization of iron selenides are interesting topics in materials sciences, due to their outstanding electrical and magnetic properties, which are sensitively dependent on their phase compositions and crystal structures [1,2,3,4]. The ferrimagnetism of Fe3Se4 and Fe7Se8 originates from the ferromagnetically aligned spins within the c-plane and antiferromagnetically coupled adjacent Fe planes with ordered iron vacancies [11]. The effect of the composition x on the magnetism of β-Fe1−xSe was not studied enough due to difficult synthesis for single phase β-Fe1-xSe. β-Fe3Se4 superstructures serve as components in the intercalated co√mpou√nd TlFe1.5Se2, which show two possible states, in which the√square√superstructure of 2 × 2 has lower energy than the rhombus ordered pattern ( 2 × 2 2 ) [17]. There was previously a rare report on the magnetic information of tetragonal β-Fe3Se4 single phase [16]
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