A. Lančok

Magnetic heating by cobalt ferrite nanoparticles

In the quest for suitable materials for hyperthermia we explored the preparation and properties of nanoparticles of Co ferrite. The material was produced by coprecipitation from water solution of Co and Fe chlorides and afterwards annealed at 400, 600 and 800 °C. The resulting particles were characterized by XRD, TEM, Mossbauer spectroscopy, and dc and ac magnetometry. The heating experiments in ac magnetic fields of various amplitudes were performed with diluted systems of particles suspended in agarose gel and the results were interpreted on the basis of the ac magnetic losses measured at various temperatures. The increase of magnetic losses and consequently of the heating efficiency with increasing temperature is explained by the strong dependence of the constant of magnetocrystalline anisotropy of Co ferrite on temperature.

Distribution of cations in nanosize and bulk Co–Zn ferrites

The structural and magnetic properties of Co(1-x)Zn(x)Fe2O4 ferrites (Co-Zn ferrites) are investigated in a narrow compositional range around x = 0.6, which is of interest because of applications in magnetic fluid hyperthermia. The study by x-ray and neutron diffraction, Mössbauer spectroscopy and magnetization measurements is done on nanoparticles prepared by the coprecipitation method and bulk samples sintered at high temperatures. In spite of the known preference of Zn2+ for tetrahedral (A) sites and Co2+ for octahedral [B] sites, the cations are distributed nearly evenly over the two sites of spinel structure and there is also a variable number of [B] site vacancies (see text), making cobalt ions trivalent. In particular for x = 0.6, the cationic distribution is refined to [Formula: see text] and [Formula: see text] for the 13 nm particles (T(C) = 335 K) and bulk sample (T(C) = 351 K), respectively.

The magnetic transition in ε-Fe2O3 nanoparticles: Magnetic properties and hyperfine interactions from Mössbauer spectroscopy

The nanoparticles of e-Fe2O3 enriched with 57Fe isotope in amorphous silica matrix were prepared by sol-gel technique starting from a single molecular precursor for both Fe2O3 and silica. From the X-ray powder diffraction pattern e-Fe2O3 was identified as the major phase and α-Fe2O3 and β-Fe2O3 were observed as minor iron oxide phases. Using the log-normal distribution for fitting the experimental data from the TEM micrographs, the characteristic size of particles d0 ∼ 25 nm was derived. The rather high coercivity of ∼2.1 T at room temperature was confirmed for our nanoparticle system. From the dependences of magnetization on temperature a two-step magnetic transition spread between 100 K and 153 K was indicated. From the 57Fe Mossbauer spectra measured in the temperature range of 4.2–300 K, the hyperfine parameters for one tetrahedral and three octahedral sites of e-Fe2O3 structure were identified. The in-field spectra in the external magnetic fields up to 6 T were taken both above and below the indicate...

CEMS studies of structural modifications of metallic glasses by ion bombardment

Fe76Mo8Cu1B15 and Fe74Nb3Cu1Si16B6 amorphous metallic alloys were exposed to ion bombardment with nitrogen ions and protons to ensure different degree of radiation damage. The radiation damage profiles were calculated in the “full cascade” mode. Conversion electron Mössbauer spectrometry was employed to scan structural modifications in the surface regions of the irradiated alloys. In Fe76Mo8Cu1B15, the irradiation with 130 keV N+ has caused a significant increase of the hyperfine magnetic fields and isomer shift due to changes in topological and chemical short-range order (SRO), respectively. No appreciable effects were revealed after bombardment with 80 keV H+ ions. Fe74Nb3Cu1Si16B6 amorphous metallic alloy was irradiated by 110 keV N+ and 37 keV H+ and only changes in chemical SRO were revealed after bombardment with nitrogen ions. The observed alternations of the structure depend primarily on the total number of displacements of the resonant atoms which are closely related to the fluence as well as type and energy of the incident ions.

Ion irradiation studies of construction materials for high-power accelerators

The paper reviews the activities and reports the current results of GSI-INTAS projects that are dealing with investigations of construction materials for high-power accelerators and their components. Three types of materials have been investigated, namely metals (stainless steel and copper), metallic glasses (Nanoperm, Finemet and Vitrovac) and organic materials (polyimide insulators and glass fiber reinforced plastics/GFRP). The materials were irradiated by different ion beams with various fluencies and energies. The influence of radiation on selected physical properties of these materials has been investigated with the aid of gamma-ray spectroscopy, transmission Mössbauer spectroscopy (TMS), conversion electrons Mössbauer spectroscopy (CEMS), optical spectroscopy (IR and UV/VIS) and other analytical methods. Some experiments were accompanied with computer simulations by FLUKA, SHIELD and SRIM codes. Validity of the codes was verified by comparison of the simulation results with experiments. After the validation, the codes were used to complete the data that could not be obtained experimentally.

Iron in spleen tissues

This contribution aims in characterization of structural positions of iron in human and horse spleen. 57Fe Mossbauer spectroscopy was employed as a principal method of investigation in addition to X-ray diffraction and transmission electron microscopy (TEM). At room temperature, ferritin nanoparticles exhibit superparamagnetic behavior due to their small dimensions. Corresponding Mossbauer spectra show doublet-like patterns. Experiments performed at low temperatures unveiled presence of magnetically split components and enabled to determine the blocking temperature. Dimensions of Fe-containing species were established from detailed analyses of TEM images.

Low temperature behavior of hyperfine fields in amorphous and nanocrystalline FeMoCuB

Low temperature (4.2 K) magnetic behavior of Fe76Mo8Cu1B15 metallic glass was studied by 57Fe Mossbauer spectrometry (MS) and 57Fe NMR. Distributions of hyperfine magnetic fields P(B) were determined for as-quenched and annealed (nanocrystalline) samples with relative fraction of the grains about 43%. P(B) distributions were derived for both the amorphous matrix and nanocrystalline grains. NMR of alloys with natural and 57Fe enriched Fe enabled to assess the contribution of 11B to the total NMR signal. P(B) distribution of the as-quenched alloy derived from MS matches reasonably well the one from NMR of the enriched sample. NMR signal from the sample with natural Fe exhibits contributions from 11B nuclei. The principal NMR lines of the annealed alloys at 47 MHz correspond to bcc Fe nanocrystals. Small asymmetry of the lines towards higher frequencies might be an indication of possible impurity atoms in the bcc structure. The observed differences between natural and enriched samples are attributed to highe...

Mössbauer spectroscopy of Basal Ganglia

Chemical states, structural arrangement, and magnetic features of iron deposits in biological tissue of Basal Ganglia are characterized. The methods of SQUID magnetometry and electron microscopy are employed. 57Fe Mossbauer spectroscopy is used as a principal method of investigation. Though electron microscopy has unveiled robust crystals (1-3 μm in size) of iron oxides, they are not manifested in the corresponding 57Fe Mossbauer spectra. The latter were acquired at 300 K and 4.2 K and resemble ferritin-like behavior.

Study of Fe‐Co Nanocomposite Films

Mossbauer study of nanogranular ferromagnetic FeCo films is presented. Two ways of production of nanocomposite systems were employed: (i) hollow cathode plasma jet deposition process, and (ii) laser ablation from Fe‐Co metallic targets by means of a KrF excimer laser and r.f. magnetron sputtering. Complementary information on the composition of the samples were obtained by nuclear magnetic resonance of 57Fe and 59Co nuclei, conversion electron Mossbauer spectroscopy, and high resolution transmission electron microscopy. The films contain crystalline nanoparticles, 5–20 nm in size, embedded in an amorphous matrix.

Proton and Nitrogen Ion Irradiation of Fe76Mo8Cu1B15 Metallic Glass

Fe76Mo8Cu1B15 amorphous metallic alloy is investigated after ion irradiation by 130 keV N+ and 80 keV H+ ions in order to ensure different degree of radiation damage. The depth of the peak region was calculated by the SRIM2008 code. Applicability of transmission and conversion electron Mossbauer effect measurements to distinguish between the bulk and surface radiation damage is demonstrated by using different irradiation conditions. The investigated alloy is characterized by weak magnetic dipole interactions due to its close‐to‐room Curie temperature. The implantation with H+ ions does not depict appreciable changes of the samples’ surfaces and practically none in the bulk. On the other hand, 130 keV N+ ions caused pronounced effects especially in the CEMS spectra, i.e. on the surface because of the short range (about 150 nm) of the irradiating particles.