Average Hyperfine Magnetic Field Research Articles

Microstructure of High‐Chromium Ferritic–Martensitic Steels for Next‐Generation Reactors

High‐chromium steels are key alloys used for the construction of technological devices in industry. Stainless steels are suitable for components that are exposed to a corrosive environment for a long time because chromium has anticorrosion properties due to segregation of chromium and the formation of a passivation layer. The physicochemical properties of the surface and the bulk of the material as well are determined by microstructure. Herein, steel NS219 is focused on, where the chromium concentration is around 13.5 wt%. In order to study the microstructure of steel, Mössbauer spectroscopy is used. Experimental results are evaluated using the binomial distribution model of the probability distribution of atoms in the nearest neighbor of the resonant atom 57Fe. Obtained spectral parameters, viz., the average magnetic hyperfine field, the average isomer shift, and the probability of the atomic configuration with no impurity atoms in the two‐shell vicinity of the iron atoms, reach saturation values from which the solubility limit of chromium in iron can be determined. On the other hand, the solubility limit of iron in Cr‐rich phase can be estimated from the value of the isomer shift of the single‐line in the spectrum annealed for the longest time.

The Interrelation between Iron Valence and Oxygen Vacancies in Substituted Orthoferrite La0.67Sr0.33FeO3– during Heat Treatment

In this paper, we studied substituted lanthanum orthoferrite La0.67Sr0.33FeO3– γ by Mössbauer spectroscopy using X-ray diffraction data. A series of vacuum annealings was performed in the temperature range of tann = 200–650°C, after which no significant changes in the structure of the samples were detected. The Mössbauer measurements at room temperature show that the Fe ions are in an average valence statebetween Fe3+ and Fe4+. Upon vacuum annealing, as the temperature tann increased, the average hyperfine magnetic field on the 57Fe nuclei and the isomer shift of the spectrum increased, which is associated with an increase in the number of vacancies and, accordingly, a decrease in the amount of Fe4+. Mössbauer measure-ments at 85 K showed that the average valence state of iron does not manifest itself. The hyperfine parameters of the low-temperature Mössbauer subspectra obtained from the model interpretation indicate that one of them belongs to Fe4+ ions, and the rest belong to Fe3+. The presence in the spectra of several sextets related to Fe3+ ions is due to the appearance of oxygen vacancies (breaking of the Fe3+–O2––Fe exchange bond) and Fe4+ ions (weakening of the Fe3+–O2––Fe exchange bond) in the nearest ionic neighborhood of Fe atoms. Both factors cause a decrease in the hyperfine magnetic field and a change in the isomer shift of the spectrum. As a result of model interpretation of the Mössbauer spectra, the numbers of oxygen vacancies and Fe4+ ions per formula unit depending on vacuum annealing temperature tann were determined for all samples. It wasshown that at tann above 450°C, the process of oxygen leaving the lattice ends and only Fe3+ ions are detected.

Field-induced spin cycloidal modulation to antiferromagnetic transition and possible flexomagnetic effect in BiFeO3 nanoparticles

Beyond its various properties, the model multiferroic BiFeO3 (BFO) displays a rich magnetic structure illustrated in the bulk by its long period (∼62 nm) spin cycloidal modulation. Here, BFO nanoparticles are produced by a facile hydrothermal method and show average size of 8 nm and a narrow size distribution, as determined using x-ray diffraction analysis and transmission electron microscopy images. Mössbauer spectrometry (MS) unambiguously reveals that a cycloidal modulation does still exists with particles about 5 times smaller than the bulk cycloid. Combining macroscopic magnetic measurements and in situ Mössbauer spectrometry, we demonstrate that a critical magnetic field of ∼0.2 T destabilizes the cycloidal modulation to lead to a homogenous antiferromagnetic state, as the result of magnetic anisotropy due to magnetoelastic and surface-confinement effects. More interestingly, further increasing of the external magnetic field up to 8 T does not change the average magnetic hyperfine field and results into multiple Mössbauer sextets we propose to explain by a flexomagnetic effect i.e. magnetic anisotropies resulting from strain gradients due to a continuous variation of the coupling between magnetization and the structural distortion from the surface to the particle core.

Pechini citrate-gel synthesised In3+ substituted X-type barium zinc hexaferrites: An investigation on structural, optical, magnetic and dielectric properties

Indium substituted X-type Ba2Zn2InxFe28-xO46 (0.0≤x≤2.0) ferrites were synthesised by a citrate-gel aqueous combustion technique, and heated at 1300 °C. XRD, FTIR, SEM with EDX, magnetic hysteresis, Mössbauer spectroscopy, UV–visible spectroscopy, and dielectric measurements up to 20 GHz have been carried out to study the modification of the structural, morphological, magnetic, optical and frequency dependant dielectric properties when indium is introduced, replacing iron in the lattice of X-type hexaferrites. XRD analysis reveals formation of a major X-type phase in all compositions. The systematic rise in lattice constants (a, c) along with cell volume (V) confirm the replacement of iron by indium. Magnetic hysteresis loops reveal a soft ferrite nature with low Mr/MS values, suggesting a multidomain structure in all samples. The HC values decrease from 22.22 kA m-1 to 12.18 kA m−1 (279 Oe to 153 Oe) with increasing indium, while magnetisation remained high between 56 A m2 /kg and 62 A m2/kg for all samples. Room temperature Mӧssbauer spectra of all samples were fitted with six Zeeman sextets of five different magnetic sublattices. It was ascertained that In-substitution reduces the Fe population in the k (spin up) sublattice, resulting in a reduction in magnetisation. The average hyperfine magnetic field <Hf> is also reported to decrease with Indium substitution for all samples. The value of the isomer shift (δ) confirmed that the iron-ions are in high spin Fe3+ state. The complex impedance and electric modulus plots reveal non-Debye type relaxation in all samples at 100 Hz to 2 MHz.

Radiation Effects in Amorphous Metallic Alloys as Revealed by Mössbauer Spectrometry: Part I. Neutron Irradiation

Iron-based amorphous metallic alloys (AMAs) of several compositions were exposed to neutron irradiation with fluences of up to 1019 n/cm2. These materials exhibit excellent magnetic properties which predetermine them for use in electronic devices operated also in radiation-exposed environments. Response of the studied AMAs to neutron irradiation is followed by Mössbauer spectrometry which probes the local microstructure. Neutron irradiation leads to rearrangement of constituent atoms, their clustering, and formation of stress centers. The observed modifications of topological short-range order result in changes of spectral parameters including average hyperfine magnetic field, ⟨B⟩, standard deviation of the distribution of hyperfine fields, and position of the net magnetic moment. After irradiation, especially differences in ⟨B⟩-values develop in two opposite directions. This apparent controversy can be explained by formation of specific atomic pairs with different exchange interactions, which depend on the composition of the samples. Part II of this paper will be devoted to radiation effects caused in Fe-based AMAs by ion irradiation.

Design and development of Ga-substituted Z-type hexaferrites for microwave absorber applications: Mössbauer, static and dynamic properties

Gallium substituted Z-type Sr3GaxCo2-xFe24O41 (x = 0.0–2.0 in steps of 0.4) hexaferrites were synthesised by the sol-gel auto-combustion process, and sintered at 1150 °C. The structural, morphology, magnetic, Mössbauer, dielectric and microwave absorption properties were examined. XRD results of x = 0.0, 0.4, 0.8, and 1.2 samples show the formation of a single Z-type hexagonal phase. The samples x = 1.6 and 2.0 show the formation of Z and M phases. Hysteresis loops analysis suggest that samples x < 1.6 possess a soft magnetic nature, while the samples x = 1.6 and 2.0 show a hard ferrite characteristics. All samples possess multi-domain microstructures. The composition x = 0.4 [maximum MS = 97.94 Am2kg−1] was fitted with seven sextets (Fe3+) and a paramagnetic doublet-A (Fe3+), while beyond x ≥ 0.8 two more doublets (Fe2+) were observed along with seven sextets in Mössbauer spectra. The maximum values of Fe2+ ions (1.26%) and relative area of paramagnetic doublets (1.91%) were observed for x = 1.6 composition, which is also responsible for the lowest value of MS (69.99 Am2kg−1) for this composition. The average hyperfine magnetic field was found to decrease, whereas average quadrupole splitting was found to increase, with Ga-substitution. The substitution of Ga ions enhanced permeability, dielectric constant, magnetic loss and dielectric loss, in a non-linear fashion. The reflection loss was maximum at lower frequencies for samples x = 0.0 and 0.8, and decreases with frequency. Sample x = 0.8 has maximum reflection loss of −12.44 dB at 8 GHz, a measured thickness of 3 mm, and a bandwidth of −10 dB at 1.18 GHz. The observed absorption has been discussed with the help of the input impedance matching mechanism and quarter wavelength mechanism. The observed coercivity in different samples also influenced microwave absorption which demonstrated potenial in microwave absorber applications.

Raman, infrared and Mössbauer spectroscopic studies of solid-state synthesized Ni-Zn ferrites

A set of Nickel-Zinc ferrite samples (Ni1-xZnxFe2O4, x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) were synthesized by the low-energy ball milling method with subsequent thermal treatment. Infrared, Raman and Mössbauer spectroscopies were used to analyze the lattice dynamics and structure of the prepared samples. Infrared studies showed a dominant absorption band ranging from 548 cm−1 to 592 cm−1 associated with cation-oxygen stretching vibrations at tetrahedral sites. The five Raman modes, predicted by factor group analysis, were observed in all spectra. All these spectra changed in symmetry because of the incorporation of Zn into the lattice, and the reordering of Fe, Ni and Zn ions in both, tetrahedral (A) and octahedral [B] sites. It is observed that Fe3+ ions located at tetrahedral sites are gradually displaced to octahedral sites by the increase of Zn2+ ions. Mössbauer spectra were collected for all samples at 295 K and at 18 K. The spectra were properly fitted by using a model that assumes that the average hyperfine magnetic field at the octahedral sites is due to a random substitution of magnetically interacting FeA3+ ions by diamagnetic ZnA2+ ions at the tetrahedral sites. It was found that the average supertransfered hyperfine field due to one FeA3+-O2+-FeB3+ superexchange interaction was equal to about 0.9 T at 18 K. The zinc contents at tetrahedral sites as obtained by Raman, Mössbauer and XRD techniques are compared and discussed.

Structural, magnetic and magnetocaloric study of Ni0.5Zn0.5Fe2O4 spinel

The objective of this work was to study the influence of annealing temperature on the structural changes and magnetic properties of the Ni0.5Zn0.5Fe2O4 spinel-type nanoparticles. The nanomaterial was prepared by the chemical co-precipitation method and studied by thermal analysis (TG–DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), magnetic measurements and 57Fe Mossbauer spectrometry. XRD has revealed that the as-prepared sample shows poor crystallization with less defined diffraction lines. As the annealing temperature increases, the diffraction peaks become intense and well defined, reflecting perfect crystallization of the sample. The estimated crystallite size varies from 25 to 83 nm. TEM observations give information on the morphology and confirm the XRD results. To quantify the proportions of the iron atoms in the tetrahedral and octahedral sites, in-field Mossbauer spectrometry measurements were carried out at low temperature. Saturation magnetization (Ms) and the average hyperfine magnetic field $$ \left( {\left\langle {B_{\text{hf}} } \right\rangle } \right) $$ increase gradually with annealing temperature. For the sample annealed at 1000 °C, the magnetic entropy change $$ \left| {\Delta S_{\text{M}}^{\hbox{max} } } \right| $$ and relative cooling power, measured under field change of 2T, are 0.67 J kg−1 K−1 and 112.5 J kg−1, respectively.

Investigation of structural, magnetic and dielectric properties of gallium substituted Z-type Sr3Co2-xGaxFe24O41 hexaferrites for microwave absorbers

Gallium substituted Z-type hexagonal ferrites with chemical composition Sr3Co2-xGaxFe24O41 (x = 0.0,0.4, 0.8, 1.2, 1.6, and 2.0) were successfully synthesised in air at 1200 °C for 5 h using the sol-gel auto-combustion technique, in order to investigate the effect of gallium substitution on structural, magnetic and dielectric properties. X-ray Diffraction (XRD) analysis of all samples reveals the formation of mixed hexaferrite phases, with Z ferrite as the major phase (72–90%).The average crystallite size of heated powders was found to be in the range of 21–40 nm. The saturation magnetisation decreases after gallium substitution, with the lowest values of 64 Am2 kg−1 for composition x = 1.6, which also hasthe highest value of coercivity (28.3 kA m−1). Nevertheless, all were soft ferrites, with Hc between 3.4 and 28.3 kA m−1.The Mr/MS ratio of all samples was found to be less than 0.5, suggesting that all the compositions possess multi-domain microstructures. Mössbauer spectroscopic analysis confirmed that the Fe ions were found in the 3 + high spin state for compositions below x ≤ 0.4, whereas ∼1.5% of the Fe ions were converted into Fe2+ high spin state beyond x ≥ 0.8 compositions, as Ga3+ began to substitute for Fe3+, forming Fe2+ in the cobalt positions. The average hyperfine magnetic field (<Hhf>) was found to be decreased with Ga-substitution. Dielectric parameters such as dielectric constant and loss factor were studied as a function of frequency, and their results show normal behaviour for ferrimagnetic materials. In complex measurements at microwave frequencies (8 GHz–12.5 GHz, the X-band), all samples had a real permittivity of around 8–14. For sample x = 2.0, a dielectric resonance peak was observed around 12.15 GHz. All showed a real permeability of around 1.0–1.4 over the frequency of 8 GHz–12.5 GHz range, and ferromagnetic resonance (FMR) was observed in x = 0.0 and 2.0 samples, at around 11 and 12 GHz, respectively. This suggests that the prepared samples can be used as microwave absorbers/EMI shielding at specific microwave frequencies. The co-existence of FMR and dielectric resonance at the same frequency of 12.15 GHz for x = 2.0 could lead to the coupling of these resonances and the development of potential metamaterials.

Study of damage in binary Fe85Cr15 alloys irradiated by ions and the effect of an external magnetic field during irradiation

Understanding radiation-induced damage in iron-chromium alloys is critical for the use of advanced steels in future fusion reactors. However, the role of the strong magnetic fields present in such magnetically confined plasma devices on material damage, though considered important, has not been thoroughly explored to date. In this work, irradiation experiments of Fe85Cr15 alloy (15% Cr content) by heavy (Fe+) and light (He+) ions have been carried out in order to characterize the damage and, additionally, the influence of an external magnetic field (B = 0.4 T) has been taken into account. The analysis of the data has been done with different techniques, the distribution of the Cr and/or vacancies around probe nuclei has been explored by Mössbauer spectroscopy and the vacancy profile by Slow Positron Annihilation Spectroscopy (SPAS). Comparison between samples irradiated by He+ and Fe+, in absence of B, reveals significant differences in the average hyperfine magnetic field (<ΔH> = 0.8 T). This can be attributed to changes in the local environment around the probe nuclei (57Fe) where either vacancies or the Cr distribution play a role. From depth-profiling by SPAS in Fe+ irradiated samples, a large concentration of vacancy-type defects is found with a profile that extends deeper than that predicted by computer simulations. Furthermore, sequential irradiation by Fe+ and He+ ions indicates that the He atoms tend to fill the vacancy clusters just in the depth where the He+ is implanted. On the other hand, small but significant differences in vacancy-type defect profiles are found between the samples irradiated both in the presence and absence of a magnetic field (B = 0.4 T) both independently of single and sequential irradiation. Detailed Mössbauer spectroscopy and SPAS analysis seem to point out that external magnetic fields could be a non-negligible parameter in the material damage due to ion irradiation.

Thermodynamic Properties, Mössbauer Study, and First-Principles Calculations of TlFe(MoO4)2

We report the results of magnetization and specific heat measurements, a 57Fe Mössbauer study of hyperfine interactions and density functional theory calculations in TlFe(MoO4)2 demonstrating two magnetic phase transitions at TN2 = 5.7 K and TN1 = 6.2 K. In the asymptotical critical region TN2 ≤ T ≤ TN1, the temperature dependence of the average hyperfine magnetic field ⟨Bhf(T)⟩ at the 57Fe nuclei is well-described by the power law ⟨Bhf(T)⟩ ∝ tβ with the static critical exponent β ≈ 0.37 inherent for a three-dimensional magnet. In this range, the Mössbauer spectra are described in terms of collinear spin-density-wave with the inclusion of high-order harmonics. The spectra of the low-temperature phase, below TN2, are well-fitted by a single six-line Zeeman pattern reflecting the equivalence of magnetic sites occupied by Fe3+ ions in an antiferromagnetic structure. The first-principles calculations allowed estimation of the strength of main exchange interactions.

X-ray diffraction, Mössbauer spectrometry and thermal studies of the mechanically alloyed (Fe1−xMnx)2P powders

(Fe1−xMnx)2P phosphide powders in the composition range 0.15 ≤ x ≤ 0.75 have been mechanically alloyed and their structural, magnetic and thermal changes with composition have been investigated by means of X-ray diffraction, 57Fe Mössbauer spectrometry, magnetization measurements and differential scanning calorimetry. The milling process induces changes in the crystal phase diagram of the (Fe1−xMnx)2P system. The XRD results reveal the coexistence of a bcc Fe(Mn)-type, hexagonal (Fe2P and Mn2P-type), orthorhombic (MnP-type) and tetragonal Fe3P-type structures for all compositions. The room temperature Mössbauer spectra confirm the formation of the Fe(Mn)-type, non-stoichiometric Fe2P-type, FeP-type and Fe3P-type structures. Saturation magnetization exhibits a comparable behavior to that of the average hyperfine magnetic field. The DSC scans show the existence of several endothermic and exothermic peaks in the temperature range (100–700) °C related to different phase transitions. The endothermic peak at about 582–589 °C can be related to the ferromagnetic/paramagnetic transition temperature (Curie temperature, TC) of the Fe(Mn)-type structure.

High frequency permeability of Fe-Cu-Nb-Si-B nanocrystalline flakes with the distribution of shape anisotropy fields

Fe-Cu-Nb-Si-B flakes with multiphase nanostructures have been obtained by annealing the amorphous ribbon and subsequently ball milled for 30 h. The crystal structures have been examined by X-ray diffraction pattern and Mössbauer spectrum. The results show that the particles annealed at 900 °C are made up of amorphous ferromagnetic phase, α-Fe3Si ferromagnetic phase and Fe2B phase, and the average hyperfine magnetic field (HBhf) of particles is 24.02 T. Meanwhile, the relationships between the structure and the high frequency permeability have been studied. Compared with particles annealed at 600 °C, particles annealed at 900 °C exhibit higher saturation magnetization, which is evidenced by the larger HBhf. Also, three magnetic loss peaks in a permeability spectrum have been observed for the particles annealed at 900 °C. The natural resonance frequencies are calculated, which are in good agreement with the experimental resonance peaks. The origin of the multiple magnetic loss peaks can be explained from the perspective of the distribution of shape anisotropy fields which is caused by multiple phase structure.

X-ray diffraction and 57Fe Mössbauer spectroscopy studies of delafossite AgFeO2 prepared by co-precipitation method

The co-precipitation method was used to prepare silver ferrite AgFeO2. The resulting powders were brick brown flakes. X-ray diffraction and Mössbauer spectroscopy were used as complementary methods to study structure and hyperfine interactions of silver ferrite. It was found that AgFeO2 has delafossite structure with two polytypes, i.e., rhombohedral 3R and hexagonal 2H, wherein the 2H polytype is dominant. The average crystallite sizes, estimated using Scherrer formula, were in the range of 15–35 nm. The Mössbauer spectrum registered at room temperature is one paramagnetic doublet with isomer shift characteristic for high-spin Fe3+ ions in an octahedral oxygen environment. In the temperature range of 3.7 K ≤ T ≤ 16 K Mössbauer spectroscopy revealed a distribution of the hyperfine magnetic fields at 57Fe nuclei connected with complicated collinear and non-collinear magnetic structure of AgFeO2. It was found that the value of the average hyperfine magnetic field monotonically decreases with an increase of temperature.

Influence of an external magnetic field on damage by self-ion irradiation in Fe90Cr10 alloy

The effect of an external magnetic field (B=0.5 T) on Fe90Cr10 specimens during Fe ion irradiation, has been investigated by means of Conversion Electron Mössbauer Spectroscopy (CEMS). The analysis has revealed significant differences in the average hyperfine magnetic field (<∆H>=0.3 T) between non-irradiated and irradiated samples as well as between irradiations made with B (w/ B) and without B (w/o B). It is considered that these variations can be due to changes in the local environment around the probe nuclei (57Fe); where vacancies and Cr distribution play a role. The results indicate that the Cr distribution in the neighbourhood of the iron atoms could be changed by the application of an external field. This would imply that an external magnetic field may be an important parameter to take into account in predictive models for Cr behaviour in Fe–Cr alloys, and especially in fusion conditions where intense magnetic fields are required for plasma confinement.

Preparation and Characterization of Amorphous Fe-B-P Ultrafine Particles

Soft magnetic Fe-B-P ultrafine particles with amorphous structure were prepared by aqueous reduction method with variable pH values. The microstructure, compositions and the soft magnetic properties of Fe-B-P submicron particles were investigated by using field emission scanning electron microscope (FE-SEM), X-Ray Diffraction (XRD), mössbauer spectrum (MS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), vibrating sample magnetometer (VSM). The results showed that a series of Fe-B-P amorphous particles with the average particle size of 0.26~0.42 μm were obtained depending on the pH value of solution. As pH value increased, the contents of B and P increased, and the specific saturation magnetization of the Fe-B-P submicron particles decreased. Some electrons, transferred from p-shell of B atoms and P atoms to 3d-shell of Fe atom, resulted in the decrease of the number of unpaired electron, which in turn led to reduction of the average hyperfine magnetic field of the Fe-B-P particles and the decrease of the magnetic torque of Fe atoms. The relation between hyperfine magnetic field (Hhf) and the specific saturation magnetization was in accord with the Marshall’s equation. At the same time, the enhancement of the shielding effect on 4s electron orbital, i.e., the density of 4s electron reduced, leading to the increase of Isomer Shift.

The influence of annealing temperature on hyperfine magnetic field and saturation magnetization of Fe–Si–Al–Cr flake-shaped particles

Fe75Si13Al10Cr2 flake-shaped particles were prepared from crushing ingots with ball milling method. In order to explore the relationship between microstructure and saturation magnetization (Ms), the particles were annealed under nitrogen atmosphere at different temperature. The XRD results show that the DO3 ordered phase coexists with α-Fe (Si, Al, Cr) matrix phase by annealing above 500 °C. Mössbauer spectroscopy measurements show that the hyperfine magnetic field (HMF) of the original particles has wide distribution. On the contrary, the HMF of the annealed powders can be easily distinguishable with each other, indicating that the crystal structure of the material has a disorder-order change. The Mössbauer spectra can be fitted with 4 sextets representing 4 different Fe-site environments, and there is a significant change on the ratios of Fe-site environments with annealing temperature. The change leads to an obviously increase of the average hyperfine magnetic field (<HMF>) with increasing annealing temperature. For this alloy, Ms has linear relationship with Fe atomic magnetic moment (μFe) and <HMF> has an approximate linear relationship with μFe. So the Ms of the particles also has an obviously increase with annealing temperature. Ms and <HMF> have an obvious turning point at 600 °C, because of the HMF values decrease of 8Fe-site and 6Fe-site, which comes from a DO3-B2 ordered transformation.

The Iron Mineralogy of Eocene Fossil Wood—a Mössbauer Study of Samples From the Petrified Forest, New Cairo, Egypt

Abstract As part of an investigation of iron species in fossil wood at the New Cairo Petrified Forest, representative samples, collected from the area, were analyzed by inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), and Mossbauer spectroscopy at room temperature. The samples are composed of silica, with ~1.2 to ~17 wt.% Fe 2 O 3 , 0.21−0.92 wt.% Al 2 O 3 , and 0.001−0.71 wt.% MnO. The other oxides—including TiO 2 , MgO, CaO, Na 2 O, K 2 O, and P 2 O 5 —constituted ~0.24 to ~1.4 wt.% of the fossil wood. Mossbauer spectra of the samples, fitted using the hyperfine distribution method, showed a major sextet of Fe 3+ in goethite (64.75–100%), another sextet of Fe 3+ in hematite (27.62–31.94%), and a doublet (2.01–5.72%) that is attributable to octahedral Fe 3+ in superparamagnetic phases. The presence of the iron in the trivalent state in all samples is consistent with high oxygen fugacity environments post-fossilization. Equivalent weights of goethite and hematite in these samples calculated using the relative spectral areas determined by Mossbauer spectroscopy and the iron contents by ICP-MS were 0.84–18.52 and 0.13–0.45 wt.%, respectively. Changes in goethite or hematite abundances in the samples had no effects on their hyperfine parameters. The observed changes in Mossbauer spectra of goethite in the samples studied have been attributed to poor crystallinity, rather than element substitutions. This resulted in a reduction of the average magnetic hyperfine field (to ~27 T) and an increase in the hyperfine field distribution widths. The effects of poor crystallinity were much less pronounced in the hematite spectrum, with the samples having average room-temperature magnetic hyperfine fields of ~50.2 T, as expected for bulk hematite. Silica substitutions for iron in the fossil wood samples cannot be ruled out, but the effects of such processes on hyperfine field distributions of the iron are unknown.

Structure and some magnetic properties of (BiFeO3) x -(BaTiO3)1−x solid solutions prepared by solid-state sintering

Abstract This paper presents the results of the study on structure and magnetic properties of the perovskite-type (BiFeO3) x -(BaTiO3)1− x solid solutions. The samples differing in the chemical composition (x = 0.9, 0.8, and 0.7) were produced according to the conventional solid-state sintering method from the mixture of powders. Moreover, three different variants of the fabrication process differing in the temperatures and soaking time were applied. The results of X-ray diffraction (XRD), Mössbauer spectroscopy (MS), and vibrating sample magnetometry (VSM) were collected and compared for the set of the investigated materials. The structural transformation from rhombohedral to cubic symmetry was observed for the samples with x = 0.7. With increasing of BaTiO3 concentration Mössbauer spectra become broadened reflecting various configurations of atoms around 57Fe probes. Moreover, gradual decreasing of the average hyperfine magnetic field and macroscopic magnetization were observed with x decreasing.

The crystal structure and magnetic properties of Ba2−xSrxCo2Fe12O22

We have synthesized the Ba2−xSrxCo2Fe12O22 samples (x = 0.1, 0.2, 0.3, 0.4, 0.5) by the solid-state reaction method and investigated their crystalline and magnetic properties by X-ray diffractometer (XRD), Mössbauer spectrometer, vibrating sample magnetometer, and network analyzer. XRD patterns show that all samples are rhombohedral with space group R-3m. The lattice constants a0 and c0 decrease with Sr substitution due to smaller ion radius of Sr2+ (1.27 Å) than that of Ba2+ (1.43 Å). The Mössbauer spectroscopy measurements show that the relative area ratios of Fe ion were maintained constant regardless of the Sr concentration. However, average magnetic hyperfine field slightly increased with the Sr concentration. This observation agrees with the fact that the saturation magnetization (Ms) linearly increases due to the increasing super-exchange interaction, originated from the difference in the ionic radius between Ba2+ and Sr2+. To investigate its properties at high frequency range, all samples were sintered at 1100 °C, and complex permeability and permittivity were measured by network analyzer between 100 MHz and 4 GHz. For x below 0.3, the initial permeability at 100 MHz increases, at higher values of x, its value decreases. Our study shows that magnetic properties of Sr2+ substitution for Ba2+ in Y-type hexaferrite as well as low magnetic loss less than 0.1 in 1 GHz band, indicating the potential application of Ba2−xSrxCo2Fe12O22 samples for RF and antenna devices in ultra high frequency band.