D. Satuła

Organophosphorous functionalization of magnetite nanoparticles

In this work magnetite nanoparticles covered by gold and silver shell were obtained. Analyzed particles were modified by two kinds of organophosphorous compounds: 3-phosphonopropionic acid and 16-phosphonohexadecanoic acid. Enzyme immobilization on particles modified in such a way was tested. The crystal structure of obtained nanoparticles was characterized by transmission electron microscopy and X-ray diffraction. Possible changes on the surfaces were analyzed by the use of infrared spectroscopy. Magnetic properties were studied by Mössbauer spectroscopy.

Thermal treatment of magnetite nanoparticles.

Summary This paper presents the results of a thermal treatment process for magnetite nanoparticles in the temperature range of 50–500 °C. The tested magnetite nanoparticles were synthesized using three different methods that resulted in nanoparticles with different surface characteristics and crystallinity, which in turn, was reflected in their thermal durability. The particles were obtained by coprecipitation from Fe chlorides and decomposition of an Fe(acac)3 complex with and without a core–shell structure. Three types of ferrite nanoparticles were produced and their thermal stability properties were compared. In this study, two sets of unmodified magnetite nanoparticles were used where crystallinity was as determinant of the series. For the third type of particles, a Ag shell was added. By comparing the coated and uncoated particles, the influence of the metallic layer on the thermal stability of the nanoparticles was tested. Before and after heat treatment, the nanoparticles were examined using transmission electron microscopy, IR spectroscopy, differential scanning calorimetry, X-ray diffraction and Mössbauer spectroscopy. Based on the obtained results, it was observed that the fabrication methods determine, to some extent, the sensitivity of the nanoparticles to external factors.

Magnetite particles studied by Mössbauer and magneto-optical Kerr effect

We present results of transmission electron microscopy, Mossbauer spectroscopy, magneto-optical Kerr effect, and magnetization measurements on magnetite-based nanoparticles M0.5Fe2.5O4 (M=Fe, Co, Mn, and Ni). Room-temperature Mossbauer spectra show ferrimagnetic behavior of the particles and suggest a preferential occupation of the B (octahedral) magnetite site by Ni and Mn cations. Magnetization measurements reveal a homogeneous magnetic-size distribution irrespective of the substitution elements. The influence of the chemical nature of the substituent on the magneto-optical Kerr spectrum is investigated. Magneto-optical magnetization loops reveal that particles in the frozen solution have the same magnetically active size as those deposited on Al substrates.

Projected iron moments in UFe4Al8 investigated with monochromatic polarized Mössbauer radiation

UFe4Al8 was investigated using a monochromatic, circularly polarized Mossbauer source. The measurements are sensitive to the sign of the hyperfine magnetic field. The iron magnetic moment component along the direction of the applied magnetic field was determined. Quantitative analysis shows that the configuration of iron moments is not collinear and, on average, only about one fourth of the atomic iron moment contributes to the total magnetization in a randomly oriented powder exposed to a field of 1 T at a temperature of 12 K. The presence of ferromagnetic clusters in an otherwise antiferromagnetic ordering is discussed. The conclusions regarding the magnetic structure are compared with the results of powder neutron diffraction experiments. In the course of the interpretation of latter, the Debye temperature D = 421(13) K was determined.

On the validity of a hyperfine magnetic field distribution measured by a monochromatic, circularly polarized Mössbauer source

It is demonstrated that when in a standard Mossbauer spectroscopy experiment two different hyperfine magnetic field distributions describe experimental data equally well, measurements by means of a monochromatic circularly polarized source lead to the correct choice of the solution. The problem of the asymmetry of the spectrum in the case of a polarized source and pure magnetic interaction is discussed and constraints for the line intensities are given.

Magnetism of the UFexAl12−x alloys

Abstract Polycrystalline samples of the ternary intermetallic alloys UFe x Al 12− x with x in the range 〈3.6–5〉 were studied. The alloys crystallize in a ThMn 12 -type structure, belonging to the space group I 4/ mmm (no. 139). Studies of the powder samples by X-ray and neutron diffraction techniques confirmed the phase homogeneity of all these materials with an iron concentration, x , below 4. The samples with a higher iron content contain a small addition of extra phases. Monochromatic circularly polarised Mossbauer source (MCPMS) measurements, carried out at 12 K in an external magnetic field of 1 T, were interpreted in terms of magnetic domains in otherwise randomly oriented powders. Magnetic moments of iron are arranged in spin-canted magnetic structures. The canting angles ( α ) were estimated. The neutron data obtained for the sample with x =4.4 indicate that the two transition temperatures, observed previously by means of the magnetisation measurements, originate in different temperatures of the ordering of iron and uranium sublattices. Our data indicate that the range of iron concentration within which two transition temperatures are observed starts with UFe 4 Al 8 alloys. However, the mechanisms underlying these transitions are different for various compositions and require further investigations. It is shown that even in the case of the magnetic domains formation of the sample the MCPMS technique can bring very valuable results.

Stability of core-shell magnetite nanoparticles.

In the paper, we present three different types of magnetite nanoparticles which were prepared from co-percipitation of iron (II) and (III) chlorides in aqueous solution with and without SiO2 and from thermal decomposition of iron (III) acetylacetonate in nonaqeous solutions. The obtained core-shell nanoparticles were tested in respect of their stability in distilled water, 10% acetic acid, 0.01 M citric acid, 0.9% NaCl and commercial white wine (12% of alcohol). Changes of the nanoparticles were examined by infrared spectroscopy, atomic absorption spectroscopy, transmission electron microscopy, X-ray diffraction and differential scanning calorimetry methods. Modification of magnetic properties was measured by Mössbauer spectroscopy.

The antiferromagnetism of (Fe1−xMnx)3P, x⩾0.67, compounds

Abstract The structural and magnetic properties of (Fe 1− x Mn x ) 3 P compounds, in the concentration range 0.67⩽ x ⩽1, have been investigated by means of X-ray and neutron diffraction experiments, magnetisation measurements, Mossbauer spectroscopy and first principles electronic structure calculations. The magnetic ordering temperatures obtained from the different techniques were consistent with each other but different from previously published results. The magnetisation curves and neutron diffraction intensities can be explained by an antiferromagnetic ordering with a magnetic unit cell four times larger than the crystallographic unit cell. The magnetic moments are small as judged from neutron diffraction and Mossbauer spectroscopy results. The band calculations on the other hand suggest a competition between Pauli paramagnetism and magnetic solutions with large magnetic moments.

The method of invariants in 57Fe Mössbauer spectroscopy on selected examples

The method of invariants is an effective tool for decomposition of Mossbauer spectra into components resulting from electric quadrupole and magnetic dipole interactions. The invariants can be next analysed to obtain all possible values of hyperfine interaction parameters. In some cases it is possible to determine the parameters with satisfactory precision. The method was applied to not fully ordered UFe4Al8. Obtained results indicate that the dominant component of the electric field gradient is negative and is oriented almost perpendicularly to the direction of the hyperfine magnetic field. Another example shows that the method of invariants results in substantial reduction of the number of calculated components in modeling of hyperfine interactions in γ-FeMn.

The influence of magnetic ordering on the transport properties of Cr–Fe–Mn alloys

Abstract In order to understand conditions in which magnetic ordering affects the electric transport properties in magnetically disordered Cr–Fe–Mn alloys, GMR was investigated in two series of samples: Cr 75+ x Fe 16+ x Mn 9− x and Cr 75+ y Fe 16− y Mn 9 . Magnetic structure of these alloys turned out to be very complex. The observed magnetoresistivity is shown to be particularly sensitive to the FM ordering.