Hyperfine Magnetic Field Values Research Articles

Room temperature magnetic ordering in very dilute Iron doped with and without selenium substitutions in antimony matrix

Mossbauer spectroscopy is one of the very sensitive tools to study the hyperfine interactions in alloys and compounds. The interaction of the probe with the local environment gives information like spin state, coordination number, magnetic and quadrupole interaction etc. In the present study, 57Fe Mossbauer spectroscopy was used to study the hyperfine interaction of the FexSb1-x-ySey bulk alloy with very dilute quantity of Fe, x = 0.002. The measurements were done at room temperature. Keeping the amount of Fe constant in the bulk alloy at x = 0.002, the concentration of Se was varied from y = 0.000, 0.004, 0.016 to 0.048. Additionally, to see the effect of extremely low concentration of Fe in Sb matrix alone, a sample with Fe concentration of 0.0015 was prepared without any Se substitution in Sb. The structural study was done using X-ray diffraction technique. Neutron depolarization study was done to see if clusters of Fe were present in the samples. The XRD spectra showed Sb peaks with no other compound phases. From Mossbauer spectroscopy, at y = 0.000, x = 0.002 one magnetic site (site A) with hyperfine magnetic field of ~312 kOe was observed. When the concentration of Fe was further reduced to x = 0.0015, there was no change in the hyperfine magnetic field of ~312 kOe. On introduction of Se into the system, we observed two magnetic sites (A and B). The value of hyperfine magnetic field (HMF) for both the sites (A and B) decreases with increases in Se concentration. At higher concentration of Se (y = 0.048) an additional nonmagnetic site (site C) with quadrupole splitting of 0.51 mm/s was also observed.

The Properties of xBiFeO3–(1 – x)SrTiO3 (x = 0.2–1.0; Δx = 0.1) Solid Solutions: Mössbauer Studies

The magnetic structure and phase transition in xBiFeO3–(1 – x)SrTiO3 solid solutions, where x is from 0.2 to 1.0 with a step of 0.1, are studied systematically with Mossbauer spectroscopy. The multiferroic BiFeO3 was modified via incorporation of a perovskite SrTiO3, and xBiFeO3–(1 – x)SrTiO3 solid solutions that possess both ferrimagnetic and ferroelectric properties at room temperature were prepared. X-ray diffraction data indicate that there are no any additional phases in the xBiFeO3–(1 – x)SrTiO3 systems, whereas Mossbauer data show that there is a mullinite (Bi2Fe4O9), when amount x of SrTiO3 in the solid solution is from 1.0 to 0.8. The Mossbauer spectra of the xBiFeO3–(1 – x)SrTiO3 system at room temperature show that when amount of BiFeO3 in the solid solution decreases, the magnetic hyperfine field values decrease as well and the widths of absorption line increase due to the weakening of the magnetic exchange interaction. The Mossbauer spectra of the systems with x < 0.5 indicate that the solid solution is paramagnetic. A relationship between the intensity of Zeeman lines and an amount of BiFeO3 in BiFeO3–(1 – x)SrTiO3 solid solution showed that the transition of this system to the paramagnetic state proceeded at room temperature, when x value was 0.4 (between x = 0.3 and 0.5).

Effect of heating temperature on structural, magnetic, and dielectric properties of Magnesium ferrites prepared in the presence of Solanum Lycopersicum fruit extract

MgFe2O4 ferrite was synthesized in the presence of Solanum Lycopersicum fruit extract using sol–gel auto-combustion technique and heated from 650 °C to 1050 °C with the difference of 100 °C. The effect of heating temperature on phase purity, crystal structure, and magnetic as well as dielectric properties was systematically investigated. XRD analysis show that all samples consist of a single phase cubic spinel structure. The average crystallite size of heated samples varied from 10 to 26 nm, it was observed that crystallite size increases with the calcination temperature and average grain size was found in between 18 and 65 nm. SEM micrographs show that there is a drastic reduction in the grain size in the sample prepared in presence of tomato extract (65 nm) compared to the sample prepared without tomato extract (373 nm) and heated at 1050 °C for 4 h. All samples belong to soft ferrite (HC ~ 10 to 70 Oe) and possess a multi-domain structure. As heating temperature increases the values of both saturation magnetization (MS) and hyperfine magnetic field (Hhf) are found to increase. The frequency-dependent dielectric phenomenon was observed in all prepared samples and single one-fourth semi-circles observed in Nyquist plot because of the contribution of the grain boundaries over the grain conductions. M″ and Z″ vs frequency plots reveal the absence of Debye relaxation in prepared compositions.

SrCoxZrxFe12−2xO19 and SrNixZrxFe12−2xO19 hexaferrites: A Comparison Study of AC Susceptibility, FC-ZFC and hyperfine interactions

This study compares the AC susceptibility, FC-ZFC and hyperfine interactions of Sr(CoxZrx)Fe12−2xO19 and Sr(NixZrx)Fe12−2xO19 hexaferrites (HFs) manufactured via ultrasonic route. The formation of M-type hexaferrites have been confirmed by X-ray powder diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR) and high-resolution transmission electron microscopy (HR-TEM) techniques. Scanning electron microscopy (SEM) presented the hexagonal-platelet morphology of products. The variation in isomer shift, line width, quadrupole splitting and hyperfine magnetic field values of them have been governed by 57Fe Mössbauer spectroscopy which showed that Co2+ and Zr4+ ions located at generally octahedral and 2b sites, while Ni2+ and Zr4+ ions located at octahedral 12k and 4f2 sites. Measurements of magnetization versus temperature (M-T) and AC susceptibility versus temperature were carried out. The various synthesized HFs displayed ferrimagnetic behavior in the temperature interval of 10–325 K. Super-spin glass-like behavior was noticed at lower temperatures. Neel-Arrhenius and Vogel-Fulcher models were used to explore the experimental AC susceptibility. It was showed that a lower Co-Zr substitution content leads to strengthen the magnetic exchange interactions, however even low Ni-Zr substitution content provoke a reduction in magnetic exchange interactions.

Impact of Eu3+ ion substitution on structural, magnetic and microwave traits of Ni–Cu–Zn spinel ferrites

Partially europium (Eu) substituted Ni0.4Cu0.2Zn0.4EuxFe2-xO4 (0.0 ≤ x ≤ 0.10) nanostructured spinel ferrites (NSFs) were produced by sol-gel auto-combustion strategy. The XRD analyses verified the existence of the single-phase composition in all the investigated samples. The Mössbauer spectra were used to estimate the values of the line-width disparity, isomeric shift (IS), quadrupole splitting, and hyperfine magnetic field (HMF). The values of HMF of the A and B sites decreased with the rise in Eu substitutions. The paramagnetic contribution of the NSFs increased with the rise in Eu3+ contents. The S-parameters of the proposed NSFs were measured using co-axial method. The frequency dispersions of the permittivity and permeability were utilized to determine the reflection losses in the 1–20 GHz frequency range. The occurrences of the natural ferromagnetic resonance (NFMR) enabled substantial absorption of the electromagnetic energy ranged from 2.5 to 9.5 GHz. There was established a strong correlation between the level of chemical substitution (x) and amplitude-frequency characteristics of the studied spinel ferrites was established. Furthermore, the increase of Eu substitution strongly influenced the frequency characteristics of the NSFs. Anomalous changing of the resonant amplitude (more than 4 times) was shown. This can be explained by the appearance of indirect exchange interactions between Fe3+ (3 d5) and Eu3+ (4f6) electronic shells. Results revealed a potential for practical applications of such kinds of materials in functional radio electronic devices.

Мёссбауэровские исследования свойств твердых растворов xBiFeO-=SUB=-3-=/SUB=--(1-x)SrTiO-=SUB=-3-=/SUB=- (x=0.2/1.0; Delta x=0.1)

Systematic Mössbauer studies of the magnetic structure and phase transition in the xBiFeO3- (1-x) SrTiO3 solid solution, where x varies from 0 to 0.8 with a step of 0.1, have been carried out. The multiferroic BiFeO3 was modified by the introduction of SrTiO3 perovskite, and solid solutions xBiFeO3- (1-x) SrTiO3 were obtained, which simultaneously possess ferrimagnetic and ferroelectric properties at room temperature. In the obtained xBiFeO3- (1-x) SrTiO3 systems, according to X-ray diffraction studies, there are no additional phases, while the Mössbauer data indicate the presence of mullinite (Bi2Fe4O9) with a SrTiO3 content in the solid solution from x = 1.0 to x = 0.8. The Mössbauer spectra of the xBiFe3- (1-x) SrTi3 system at room temperature show that with a decrease in the amount of BiFeO3 in the solid solution, the magnetic hyperfine field values ​​decrease and the absorption line widths increase due to the weakening of the magnetic exchange interaction. For compositions with x &lt;0.5, the Mössbauer spectra indicate the paramagnetic state of the solid solution. Based on the dependence of the Zeeman line intensity on the BiFeO3 content in the xBiFeO3- (1-x) SrTiO3 solid solution, it was found that the transition to the paramagnetic state of the xBiFeO3- (1-x) SrTiO3 system at room temperature occurs near the value x = 0.4 (between x = 0.3 and x = 0.5).

Mössbauer study and magnetic properties of Fe–Si–B–Cu amorphous systems with minor substitution of carbon

The effect of minor substitution of carbon on the structure and magnetic properties of Fe–Si–B–Cu-type metallic glasses was investigated. Structural investigations performed at room temperature with Mossbauer spectroscopy and X-ray diffractometry confirmed amorphous nature of the as-quenched ribbons. Average values of hyperfine magnetic fields do not significantly differ with respect to the minor changes in the metalloid contents (up to 1 at.%). No fluctuations were found in the chemical short-range order (SRO). Only structural deviations in topological SRO were revealed that were confirmed also by DSC and mTGA techniques via changes in the crystallization and Curie temperatures caused by compositional modifications. In addition, magnetic measurements show that substitution of C for Fe leads to slightly higher saturation magnetization corresponding to parallel orientation of the external magnetic field with respect to the plane of the ribbon.

Antiferromagnetic ordering in lithium deintercalated Fe1−xZnxPO4: A Mössbauer spectroscopy study

Abstract Various compositions of Fe1−xZnxPO4 (x = 0.1, 0.2, 0.3, and 0.5) were synthesized by solid-state reaction and chemical lithium deintercalation processes, and their magnetic properties were characterized based on Mossbauer analysis. The synthesized Fe1−xZnxPO4 have orthorhombic structures with space group Pnma. The magnetization curves of Fe1−xZnxPO4 show the antiferromagnetic behaviors and magnetic phase transition caused by the strong crystal field in the FeO6 octahedral sites. The Neel temperature (TN) of Fe1−xZnxPO4 for x = 0.1, 0.2, 0.3, and 0.5 was found to be 97, 82, 63, and 62 K, respectively. Mossbauer spectra below TN appeared to have eight Lorentzian lines with antiferromagnetic ordering. The charge state of Fe ions is the high spin state of Fe3+, as characterized by an isomer shift (δ = 0.28–0.43 mm/s). The value of magnetic hyperfine field (Hhf) decreased with increasing Zn concentration because the superexchange interaction via Fe–O–Zn link is weaker than that via Fe–O–Fe link. Also, the value of electric quadrupole splitting (ΔEQ) gradually decreased with increasing Zn concentration due to the substitution of a Zn ion for the Fe ion, inducing a change in the charge asymmetry at the FeO6 sites. The Debye temperatures are found to decrease with increasing Zn concentration.

AC susceptibility and hyperfine interactions of Mg-Ca ions co-substituted BaFe12O19 nanohexaferrites

Magnesium and calcium co-substituted Ba M-type nanohexaferrite (NHFs) is fabricated via sol-gel auto-combustion technique. The phase formation was proved by XRD powder pattern, FESEM and HR-TEM. Magnetic properties of Ba1-2xCaxMgxFe12O19 (x ≤ 0.1) NHFs investigated by Mossbauer Spectroscopy. The variations in line width, quadrupole splitting, isomer shift, the cation distribution of Ca2+ and Mg2+ ions and hyperfine magnetic field values were estimated. The AC magnetic susceptibility and ZFC-FC measurements were also performed for the Ba1-2xCaxMgxFe12O19(x = 0.02 and 0.08) NHFs. The MFC-MZFC results do not show blocking temperature peak, indicating the ferrimagnetic (FM) behavior of prepared products. Different models including Neel-Arhenius (N-A), Vogel-Fulcher (V-F) and critical slowing down (CSD) were tested to evaluate the AC-magnetic susceptibility behaviors. It is demonstrated that the magnetic interactions are important for x = 0.02 NHFs.

Manganese/Yttrium Codoped Strontium Nanohexaferrites: Evaluation of Magnetic Susceptibility and Mossbauer Spectra.

Manganese (Mn)- and yttrium (Y)-substituted Sr-nanohexaferrites (MYSNHFs) of composition Sr1−xMnxFe12−xYxO19 (with 0.0 ≤ x ≤ 0.5) were prepared by citrate sol-gel autocombustion method. As-prepared MYSNHFs were characterized via diverse analytical techniques to determine the influence of Mn and Y cosubstitution on their microstructures and magnetic properties. 57Fe Mössbauer spectra of the MYSNHFs were used to evaluate the variation in the line width, isomer shift, quadrupole splitting, and hyperfine magnetic field values. It was shown that the dopant ions could preferentially occupy the 12k, 4f2, and 2b sites. Furthermore, the observed shift in the blocking temperatures of the studied MYSNHFs towards lower values with rising Mn2+ and Y3+ contents was attributed to the overall particles size reduction. Meanwhile, the AC susceptibility of the proposed MYSNHFs revealed that the magnetic interactions were weakened with the increase in dopant contents which was ascribed to the replacement of both Sr2+ and Fe3+ ions by the Mn2+ and Y3+ dopants.

AC susceptibility and hyperfine interactions of vanadium substituted barium nanohexaferrites

Vanadium ions substituted BaFe12O19 nanohexaferrites, BaFe12-xVxO19 (0.0 ≤x ≤ 0.1), were produced through the sol-gel auto-combustion route. The structure, morphology and the elemental compositions of various products were examined using X–ray powder diffraction, scanning electron microscopy coupled with EDX and EDS elemental mapping. These techniques confirmed the formation of the desired Ba-nanohexaferrite phases. The crystallites size was found to be 55–58 nm range for all products. The magnetic properties of BaFe12-xVxO19 nanohexaferrites were investigated by Mossbauer spectroscopy, ZFC-FC magnetizations and AC susceptibility. The evolutions in the values of hyperfine magnetic field, isomer shift, quadrupole splitting, and line width were deduced via Mossbauer analysis. The experiments of ZFC and FC magnetizations indicated that no blocking temperature is observed in the temperature interval 2–400 K, which signals the typical ferromagnetic (FM) behavior for the produced nanohexaferrites. A super-spin glass like behavior is noticed at lower temperatures. The experiments AC susceptibility confirmed that the strength of magnetic interactions is enhanced for lower content of V3+ (x = 0.02). For higher amount of V3+, the magnetic interactions are weakened. The obtained results are mainly accredited to the substitutions of Fe3+ ions by V3+ ions.

Effect of Ce3+ Ion on Structural and Hyperfine Interaction Studies of Co0.5Ni0.5Fe2−xCexO4 Ferrites: Useful for Permanent Magnet Applications

Nanoparticles of Co0.5Ni0.5Fe2−xCexO4 (where x = 0.0, 0.01, 0.015 and 0.02) ferrites are prepared by the modified solution combustion method using a mixture of fuels and are characterized to understand their structural, microstructural and magnetic properties. The X-ray diffraction is used to confirm the formation of a single-phase cubic spinel structure. The average crystallite sizes are calculated using the Scherrer formula and are found to be less than 50 nm. The microstructural features are obtained by the scanning electron microscopy, and the compositional analysis is done by using the energy-dispersive spectroscopy. The transmission electron microscopy (TEM) investigations show that the synthesized ferrites are made up of very fine spherical nanoparticles. The influence of a rare-earth element (Ce3+) on the magnetic properties of the samples was studied using the Mossbauer spectroscopy. The Mossbauer spectroscopy reveals the formation of broadened Zeeman lines and quadrupole-split lines and the presence of the Fe3+ charge state at B sites in the samples. The quadrupole splitting shows that the orientation of the magnetic hyperfine field with respect to the principle axes of the electric field gradient was random. The magnetic hyperfine field values indicate that the A sites have more A-O-B superexchange interactions than the B sites. The coexistence of magnetic sextet and a doublet component on the room-temperature spectra suggests superparamagnetic properties of the nanoparticles. The low-temperature (15 K) Mossbauer spectroscopy explores the paramagnetic relaxation in the nanoparticles. The area under the sextet refers to Fe3+ concentrations in the tetrahedral and octahedral sites of the ferrite. This study confirms that the Ce3+ substitution of Fe3+ only for octahedron sites causes the decrease in Fe-O-Fe arrangement. The effect of Ce3+ doping on the magnetic properties of Co0.5Ni0.5Fe2O4 is examined from the vibrating sample magnetometry (VSM) spectra. Saturation magnetization values are decreased initially and then increased, as result of Ce3+ doping. This can be explained by Neel’s two-sub-lattice model. Further, the value of coercivity is found to be increasing with increasing Ce3+ concentration. The obtained results of M-H loop with improved coercivity (from 851 to 1039 Oe) by Ce3+ doping of Co0.5Ni0.5Fe2O4 demonstrate the usefulness for permanent magnet applications.

Substitution effect of Cr3+ on hyperfine interactions, magnetic and optical properties of Sr-hexaferrites

Chromium-substituted strontium nano-hexaferrites, SrCrxFe12-xO19 (0.0 ≤ x ≤ 1.0), were produced by the hydrothermal route. The structure, morphology, optical and magnetic properties were studied. Crystal structure, spinel phase and functional groups were verified using X-ray diffraction and Fourier Transform Infrared spectroscopy. The average crystallites size is ranging between 50 and 67 nm. Scanning electron microscopy observations indicated that the multi-grains of the particles are aggleromated and are hexagonal in shape. The isotherm plots obtained from the nitrogen physisorption experiments showed that the mesopore area and the total pore volume decreased progressively with increasing the Cr3+ content. Besides, the band gap energy (Eg) decreases from 1.75 to 1.43 eV. The magnetic hysteresis loops showed that the produced nano-hexaferrites exhibit hard ferromagnetic-like (FM) behavior. Compared to the pristine SrFe12O19 product, the deduced saturation (Ms) and remanent (Mr) magnetizations, the coercivity (Hc) and the magnetocrystalline anisotropy field (Ha) increase for lower Cr3+ content (x ≤ 0.4) and then decrease as the Cr3+ content further increases. The squareness ratio Mr/Ms are ranging between 0.5 and 0.6, suggesting the single domain nano-sized particles with uniaxial anisotropy for various synthesized products. Mossbauer analysis was done to determine the quadrupole splitting, the isomer shift, and the hyperfine magnetic field values of all products.

Hydrothermal synthesis of CoyZnyMn1-2yFe2O4 nanoferrites: Magneto-optical investigation

Manganese ferrites nanoparticles (NPs) substituted with both Co2+ and Zn2+ simultaneously (CoyZnyMn1-2yFe2O4 NPs for y=0.0 to 0.5), have been produced by hydrothermal approach. The substitution with both Co2+ and Zn2+ ions on the structure, spectroscopic and magneto-optical properties of nanocrystalline MnFe2O4 spinel ferrites have been analyzed in detail. The formation of spinel phase and structural changes induced by Co2+ and Zn2+ ions substitutions were confirmed by X-ray diffraction studies. Rietveld refinement revealed the cubic spinel phase for all products (minor amount of Fe2O3). Lattice constant and crystallite size were found to decrease from 8.478 to 8.370Å and from 14.68 to 8.22nm, respectively with increasing substitution of Co2+ and Zn2+ ions. HR-SEM and HR-TEM micrographs revealed the high homogeneity cubic structure of samples. The hyperfine magnetic field values for all products after Mn2+, Zn2+ and Co2+ ions substitution were determined by Mössbauer analysis. The estimated optical Eg (Energy band gap) values are in the range of 1.41–1.54eV for the samples. The smaller Eg values are mainly attributed to greater particle size and decreasing quantum confinement effect.

Magneto-optical properties of BaCryFe12−yO19 (0.0 ≤ y ≤ 1.0) hexaferrites

In this study, nanocrystalline BaCryFe12−yO19 (0.0 ≤ y ≤ 1.0) hexaferrite powders were prepared by sol–gel auto combustion method and the effect of Cr3+ ion substitution on morphology, structure, optic and magnetic properties of Barium hexaferrite were investigated. X-ray powder diffraction (XRD) analyses confirmed the purity of all samples. The XRD data shows that the average crystallite size lies between 60.95 nm and 50.10 nm and same was confirmed by Transmission electron microscopy. Transmission electron and scanning electron microscopy analyses presented the hexagonal morphology of all products. The characteristic hysteresis (σ-H) curves proved the ferromagnetic feature of as grown nanoparticle samples. Specific saturation magnetization (σs) drops from 46.59 to 34.89 emu/g with increasing Cr content while the coercive field values lie between 770 and 1652 Oe. The large magnitude of the magnetocrystalline (intrinsic) anisotropy field, (Ha) between 11.0 and 12.6 kOe proves that all products are magnetically hard. The energy band gap values decrease from 2.0 eV to 1.84 eV with increasing Cr content. From 57Fe Mössbauer spectroscopy, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values were determined and discussed.

Mössbauer spectroscopy of MgxCu0.5−xZn0.5Fe2O4 (x = 0.0, 0.2 and 0.5) ferrites system irradiated by γ-rays

The effect of the Mg-content on the cation distribution of cubic MgxCu0.5−xZn0.5Fe2O4(x = 0.0, 0.2, 0.3, 0.5) prepared by conventional ceramic method was investigated using Mössbauer spectroscopy at room temperature. We aimed to estimate the enhanced changes in the inversion parameter of MgxCu0.5−xZn0.5Fe2O4 system due to γ-ray irradiation as a function of the Mg-content in the range 0.5 ≥ x ≥ 0.0. The samples were irradiated by 1173 keV + 1332.5 keV γ-rays emitted from 60Co radioactive source. The total absorbed dose was 1.9 MGy with dose rate 5 kGy/h. The observed superposition of more than one sextet that belong to either octahedral [B] or tetrahedral (A) sites in the Mössbauer spectra before and after γ-irradiation was interpreted by the effect of spin canting. Moreover, there is an evidence on the presence of the Fe2+ charge state at A-sites in the irradiated samples. The quadrupole splittings showed that the orientation of the magnetic hyperfine field with respect to the principle axes of the electric field gradient was random. The magnetic hyperfine field values indicated also that the A sites had more A-O-B super exchange interactions than the B sites. New antistructure modeling for the pristine and irradiated MgxCu0.5−xZn0.5Fe2O4 samples at different γ-doses was used for describing of the lattice defects and surface centers.

Synthesis and Structural and Magnetic Characterization of BaZn x Fe12−x O19 Hexaferrite: Hyperfine Interactions

To study the effect of Zn substitution on structural magnetic properties and hyperfine interactions of barium hexaferrite, BaFe12−xZnxO19 (0.0≤x≤0.3) hexaferrites were synthesized via sol-gel auto-combustion technique. Rietveld analysis of XRD powder patterns confirmed the formation of single-phase hexaferrites for all products. Due to the larger ionic size of Zn2+ as compared with Fe3+, while x increases, the lattice constant parameters increase to a small degree. Nanoplate morphology of the products is presented by SEM analyses. It was observed that both saturation magnetization and coercivity decrease in almost the same manner with zinc concentration for all substitutions. Cation distribution calculations showed that Zn2+ occupies 12k, 4 f2, 4 f1, and 2b sites and at the same time pushes Fe3+ ions towards 2a and 12 k1 sites. From57Fe Mossbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting, and hyperfine magnetic field values on Zn2+ substitution have been determined.

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.

Microwave, dielectric and magnetic properties of Mg-Ti substituted Ni-Zn ferrite nanoparticles

Mg-Ti substituted Ni-Zn spinel ferrites (Ni0.5Zn0.5MgxTixFe2−2xO4, where 0.05≤x≤0.25) have been prepared by conventional solid state reaction method. 1wt% B2O3 was added to increase the crystal growth at low temperatures. The structural characterization of samples was performed by X-ray powder diffractometry, scanning electron microscopy and Mössbauer spectroscopy. Magnetic parameters of samples were measured by vibrating sample magnetometer at room temperature. Microwave characteristics were determined by near field measurements using a network analyzer in reflection/transmission mode. Mössbauer spectra of all the samples consist of 3 sextets and one doublet. Variation of the line width, isomer shift, quadrupole splitting and hyperfine magnetic field values have been obtained from the 57Fe Mössbauer spectroscopy data for Ni-Zn spinels having different Mg2+ and Ti4+ concentrations. The saturation magnetization of the samples decreases as the concentration of Mg-Ti ions increases, which can be explained by site preferences of the substituted cations. The electrical properties of Mg-Ti substituted Ni-Zn spinel ferrites were examined extensively as a function of temperature, frequency and Mg-Ti amount. It was found that Mg-Ti substitution has a strong effect on the ac conductivity, dielectric constant and dielectric loss mechanisms. The activation energy levels can be regulated by varying Mg-Ti concentration. There is one reflection minimum observed in the microwave characterization of the samples in the 2–18GHz range located around 10GHz in X-band, the mechanism of which is the quarter wave cancellation due to the matching thickness. The Ni0.5Zn0.5Mg0.2Ti0.2Fe1.6O4 sample has the best microwave properties with the reflection loss of −29dB at 10.4GHz for a thickness of 3mm and better than −35dB at 16GHz when thickness is decreased to 2mm. As a result, it was concluded that this material can be used as microwave absorber both in X and Ku-bands.

Synthesis and characterization of oleylamine capped MnxFe1-xFe2O4 nanocomposite: Magneto-optical properties, cation distribution and hyperfine interactions

Pure Fe3O4 NPs and Oleylamin (OAm) capped MnxFe1-xFe2O4 (MnxFe1-xFe2O4@OAm) (0.2 ≤ x ≤ 1.0) nanocomposites (NCs) were synthesized by the polyol route. Lattice parameter increases with increasing Mn2+ concentration, due to the respective larger ionic radius of Mn2+ ion compared with the Fe2+ ion. The VSM analyses revealed superparamagnetic characteristics of all samples. The extrapolated specific saturation magnetization (σs) values decreased from maximum 50.74 emu/g to minimum 15.34 emu/g by increasing Mn content. The particle size dependent Langevin function was applied to determine the magnetic particle dimensions (Dmag) between 9.10 nm and 21.50 nm. The observed magnetic moments of NPs and NCs are in range of (0.64–2.10) μB and significantly less than 4 μB of bulk Fe3O4. Magnetic anisotropy was determined as uniaxial and calculated effective anisotropy constants (Keff) are between 32.14 × 104 Erg/g and 8.71 × 104 Erg/g. The size dependent saturation magnetization suggests the existence of a magnetically dead layers around the magnetic cores for NCs between 0.72 nm and 1.29 nm. From 57Fe Mössbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values on Mn2+ substitution have been determined. Although, the Mössbauer spectra for the sample x = 0.2 is composed of ferromagnetic sextets, paramagnetic doublet is also formed for other samples. The percent diffuse reflectance spectroscopy (DR %) and Kubelka-Munk theory were used to specify the optical properties. The estimated optical band gap (Eg) values from Tauc plots are between 1.50 eV and 2.05 eV. Increasing Mn content in NCs increased the band gap at different magnitudes.