Structural, magnetic, and electronic properties of iron selenide Fe6-7Se8 nanoparticles obtained by thermal decomposition in high-temperature organic solvents

Abstract

Iron selenide nanoparticles with the NiAs-like crystal structure were synthesized by thermal decomposition of iron chloride and selenium powder in a high-temperature organic solvent. Depending on the time of the compound processing at 340 °C, the nanocrystals with monoclinic (M)-Fe3Se4 or hexagonal (H)-Fe7Se8 structures as well as a mixture of these two phases can be obtained. The magnetic behavior of the monoclinic and hexagonal phases is very different. The applied-field and temperature dependences of magnetization reveal a complicated transformation between ferrimagnetic (FRM) and antiferromagnetic (AFM) structures, which can be related to the spin rotation process connected with the redistribution of cation vacancies. From XRD and Mössbauer data, the 3c type superstructure of vacancy ordering was found in the hexagonal Fe7Se8. Redistribution of vacancies in Fe7Se8 from random to ordered leads to the transformation of the magnetic structure from FRM to AFM. The Mössbauer data indicate that vacancies in the monoclinic Fe3Se4 prefer to appear near the Fe(3+) ions and stimulate the magnetic transition with the rotation of the Fe(3+) magnetic moments. Unusually high coercive force Hc was found in both (H) and (M) nanocrystals with the highest ("giant") value of about 25 kOe in monoclinic Fe3Se4. This is explained by the strong surface magnetic anisotropy which is essentially larger than the core anisotropy. Such a large coercivity is rare for materials without rare earth or noble metal elements, and the Fe3Se4-based compounds can be the low-cost, nontoxic alternative materials for advanced magnets. In addition, an unusual effect of "switching" of magnetization in a field of 10 kOe was found in the Fe3Se4 nanoparticles below 280 K, which can be important for applications.

Mössbauer study of magnetism in Fe3Se4

“…[11] The phase has also been studied for a potential application as a hard magnetic material. [12,13] The aim of this work is to study the properties of the magnetically ordered Fe atoms both above and below T C using Mössbauer spectroscopy.…”

The Oligomeric Form of the Escherichia coli Dps Protein Depends on the Availability of Iron Ions

“…It clearly differs from that of Fe(NH4) 2 (SO 4 ) 2 alone ( Figure 2 G). The spectrum was processed by the UNIVEM program [ 26 ], and was approximated by two quadrupole doublets with isomeric shift (δ) and quadrupole splitting (ΔE Q ) characteristic for 10 nm spherical nanoparticles of magnetite (Fe 3 O 4 ) in the paramagnetic state [ 27 ]. Magnetite Fe 3 O 4 contains both Fe 2+ and Fe 3+ ions (mixture of FeO and Fe 2 O 3 in variable proportions).…”

Temperature-responsive nanomagnetic logic gates for cellular hyperthermia

“…9 With this rich phase diagram, phase purity was the first hurdle to overcome in the design of a successful chemical route for the synthesis of Fe 3 Se 4 nanocrystals. The current approach to prepare phase pure Fe 3 Se 4 nanoparticles is based on the thermal decomposition of iron and selenium precursors at intermediate temperatures (300 to 340 1C), 10,11 where FeSe 2 nuclei formed during the heating ramp are transformed into Fe 3 Se 4 . However, without exceptions, this approach leads to nanoparticles and nanostructures with poor control over size, shape and the aggregation state, [10][11][12][13][14] leading to poor control over the magnetic properties and stability of colloidal dispersions of Fe 3 Se 4 nanoparticles.…”

“…Within well-defined windows of concentrations, reaction temperatures and ramp slopes, a dramatic improvement in the control over size, shape homogeneity and distribution is obtained, exceeding those of state-of-the-art methods. [10][11][12][13][14] Within these windows, quasi-hexagonal nanoplatelets with lateral average diameters ranging from 90 to 300 nm and thicknesses between 40 and 60 nm are obtained (Fig. 1 and Fig.…”