Magnetic Hyperfine Field Research Articles

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.

Study of phase transformations, structural, corrosion properties and cytotoxicity of magnetite-based nanoparticles

This paper presents the results of the structural, corrosion, magnetic properties and cytotoxicity of magnetite nanoparticles, phase transformations was studied by thermal annealing. It was established that thermal annealing of Fe3O4 nanoparticles led to three stages of phase transformations from magnetite to maghemite, with the subsequent formation of the hematite structure. Increasing annealing temperature lead to a change in the magnitudes of the hyperfine magnetic field, quadrupole displacement and isomeric shift that indicates a change in the crystal structure and annealing of defects, which eventually leads to the ordering of magnetic nanoparticles. Studying the degradation of nanoparticles in PBS solution shows us that a change in the crystal structure as a result of a decrease in the degree of perfection and the formation of amorphous inclusions leads to magnetic disordering and a subsequent change in the magnitude of the hyperfine magnetic field. Cytotoxicity results indicate that nanoparticles do not show cytotoxic activity against tested L929, PC-3 and HeLa cell lines, because in all experimental series metabolic activity of studies cells was not below 70% of control.

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.

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.

Bandwidth controlled insulator-metal transition in BaFe2S3 : A Mössbauer study under pressure

BaFe$_2$S$_3$ is a quasi one-dimensional Mott insulator that orders antiferromagnetically below 117(5)\,K. The application of pressure induces a transition to a metallic state, and superconductivity emerges. The evolution of the magnetic behavior on increasing pressure has up to now been either studied indirectly by means of transport measurements, or by using local magnetic probes only in the low pressure region. Here, we investigate the magnetic properties of BaFe$_2$S$_3$ up to 9.9\,GPa by means of synchrotron $^{57}$Fe M\"ossbauer spectroscopy experiments, providing the first local magnetic phase diagram. The magnetic ordering temperature increases up to 185(5) K at 7.5\,GPa, and is fully suppressed at 9.9\,GPa. The low-temperature magnetic hyperfine field is continuously reduced from 12.9 to 10.3\,T between 1.4 and 9.1\,GPa, followed by a sudden drop to zero at 9.9\,GPa indicating a first-order phase transition. The pressure dependence of the magnetic order in BaFe$_2$S$_3$ can be qualitatively explained by a combination of a bandwidth-controlled insulator-metal transition as well as a pressure enhanced exchange interaction between Fe-atoms and Fe 3\textit{d}-S 3\textit{p} hybridization.

161Dy Time‐Domain Synchrotron Mössbauer Spectroscopy for Investigating Single‐Molecule Magnets Incorporating Dy Ions

AbstractTime‐domain synchrotron Mössbauer spectroscopy (SMS) based on the Mössbauer effect of 161Dy has been used to investigate the magnetic properties of a DyIII‐based single‐molecule magnet (SMM). The magnetic hyperfine field of [Dy(Cy3PO)2(H2O)5]Br3⋅2 (Cy3PO)⋅2 H2O⋅2 EtOH is with B0=582.3(5) T significantly larger than that of the free‐ion DyIII with a 6H15/2 ground state. This difference is attributed to the influence of the coordinating ligands on the Fermi contact interaction between the s and 4f electrons of the DyIII ion. This study demonstrates that 161Dy SMS is an effective local probe of the influence of the coordinating ligands on the magnetic structure of Dy‐containing compounds.

161 Dy Time-Domain Synchrotron Mössbauer Spectroscopy for Investigating Single-Molecule Magnets Incorporating Dy Ions.

Time-domain synchrotron Mössbauer spectroscopy (SMS) based on the Mössbauer effect of 161 Dy has been used to investigate the magnetic properties of a DyIII -based single-molecule magnet (SMM). The magnetic hyperfine field of [Dy(Cy3 PO)2 (H2 O)5 ]Br3 ⋅2 (Cy3 PO)⋅2 H2 O⋅2 EtOH is with B0 =582.3(5) T significantly larger than that of the free-ion DyIII with a 6 H15/2 ground state. This difference is attributed to the influence of the coordinating ligands on the Fermi contact interaction between the s and 4f electrons of the DyIII ion. This study demonstrates that 161 Dy SMS is an effective local probe of the influence of the coordinating ligands on the magnetic structure of Dy-containing compounds.

Study on velocity mode of 57Fe Mӧssbauer spectroscopy and determination of lattice dynamics in Fe3S4

Abstract 57Fe Mӧssbauer spectroscopy studies on chemically synthesized greigite Fe3S4 have been conducted with a unique velocity mode, known as constant velocity with slope, which allows detection of subtle changes and in-depth details of sextets in the spectra. Accurate determination of the overlapped sub-spectra corresponding to tetrahedral Fe3+ (A) and octahedral Fe2.5+ (B) sub-lattices has been made based on the special velocity mode. Estimation of Debye temperature θD from the temperature dependent central shift (CS) values gives the values: 805 ± 10 K and 760 ± 10 K for A- and B-sites, respectively. The discrepancy of two θD values reveals different lattice vibration between A- and B-sites. The Lamb-Mӧssbauer factor ratio fB/fA is found to be 0.98 at room temperature. The different low-temperature behaviors of hyperfine magnetic field for tetrahedral A- and octahedral B-sites are observed.

Influence of structure effects and orbital ordering on the magnetic hyperfine field in pyrochlore oxides R2V2O7 (R = Lu, Yb, Tm, Er, Ho): ab initio calculations

Influence of structure effects and orbital ordering on the magnetic hyperfine field in pyrochlore oxides R2V2O7 (R = Lu, Yb, Tm, Er, Ho): ab initio calculations

Impact of La3+ and Y3+ ion substitutions on structural, magnetic and microwave properties of Ni0.3Cu0.3Zn0.4Fe2O4 nanospinel ferrites synthesized via sonochemical route.

In the current study, Ni0.4Cu0.2Zn0.4LaxYxFe2−xO4 (x = 0.00 − 0.10) nanospinel ferrites (NSFs) were fabricated via an ultrasonic irradiation route. The creation of single phase of spinel nanoferrites (NSFs) was investigated by X-ray powder diffractometry (XRD) and selected area diffraction pattern (SAED). The cubic morphology of all samples was confirmed by scanning and transmission electron microscopies (SEM and TEM) respectively. The UV-Vis investigations provided the direct optical energy band gap values in a narrow photon energy interval of 1.87–1.92 eV. The 57Fe Mössbauer spectroscopy analysis explained that the hyperfine magnetic fields of Octahedral (Oh) and Tetrahedral (Td) sites decreased with substitution. The paramagnetic properties of NPs decrease with increase of content of doped ions. Investigations of magnetic properties reveal a superparamagnetic nature at 300 K and soft ferromagnetic trait at 10 K. The Ms (saturation magnetization) and Mr (remanence) decrease and the Hc (coercivity) increases slightly with La3+ and Y3+ substitution. The observed magnetic traits are deeply discussed in relation with the morphology, structure, magnetic moments and cation distributions. The microwave characterization of the prepared NSFs showed that, dissipation (i.e., absorption) of incoming microwave energy occurs at a single frequency, for each sample, lying between 7 and 10.5 GHz. The reflection losses (RL) at these frequencies range from −30 to −40 dB and the mechanism of which is explained in the framework of dipolar relaxation and spin rotation. The best microwave properties were obtained with a LaY concentration of x = 0.08 having an RL of −40 dB @ 10.5 GHz and an absorption bandwidth of 8.4 GHz @ −10 dB. With these high values of RL and absorbing bandwidth, LaY doped NiCuZn NSF products would be promising candidates for radar absorbing materials in the X-band.

Mössbauer Studies of BaCoZnFe&lt;SUB&gt;16&lt;/SUB&gt;O&lt;SUB&gt;27&lt;/SUB&gt; W-type Hexaferrite

A polycrystalline BaCoZnFeSUB16/SUBOSUB27/SUB sample was prepared by the solid-state reaction method and wet ball-milling. The refined X-ray diffraction patterns revealed that the prepared sample was hexagonal with the space group P63/mm. To determine the spin transition temperature (TSUBS/SUB), the temperature dependence of the zero-field-cooled magnetization curves were measured under applied fields of 100 to 1000 Oe at various temperatures ranging from 4.2 to 295 K. TSUBS/SUB is the temperature at which the spin changes from the planar to the conical direction at the 135 K. From the hysteresis curves at various temperatures ranging from 4.2 to 295 K, the coercivity showed a change in slope at TSUBS/SUB. Mössbauer spectra were obtained at various temperatures ranging from 4.2 to 295 K, and the magnetic hyperfine field and electric quadrupole splitting of the sample showed abrupt changes around TSUBS/SUB.

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.

Forced hydrolysis of FeCl3 solutions in the presence of sodium dextran sulphate

The effect of sodium dextran sulphate (Mw = 500,000) on the forced hydrolysis of FeCl3 solutions was investigated using a microwave-assisted method. Reference samples obtained upon 10 to 120 min of forced hydrolysis of the FeCl3 solution showed the presence of an α-Fe2O3 phase alone. After 10 min of the forced hydrolysis of FeCl3 in the solution containing sodium dextran sulphate, α-Fe2O3 and additionally β-FeOOH precipitated. The Mossbauer spectra of α-Fe2O3 precipitated in the presence of sodium dextran sulphate showed a significant broadening of spectral lines accompanied by decreased values of the hyperfine magnetic field. This was explained by lower α-Fe2O3 crystallinity. The FESEM of reference α-Fe2O3 samples showed cube-like particles of good uniformity in the submicrometer range. In the presence of dextran sulphate polymer, the α-Fe2O3 particles of varying sizes and close to egg-like shape were obtained as a result of the specific adsorption of sulphates on the oxide surface and steric conditions created by dextran branches.

Microscopic phase diagram of LaFeAsO single crystals under pressure

We investigated LaFeAsO single crystals by means of synchrotron M\"ossbauer spectroscopy under pressures up to 7.5 GPa and down to 13 K and provide a microscopic phase diagram. We found a continuous suppression of the magnetic hyperfine field with increasing pressure and it completely vanishes at $\sim$ 7.5 GPa which is in contrast to the behavior in polycrystalline samples where the magnetic order vanishes at $\sim$ 20 GPa. The different behavior of the polycrystalline samples might be due to As-vacancies. Our results are in qualitative agreement with density functional theory calculations where a reduction of the magnetic moment with increasing pressure was found. We found that among different samples at ambient pressure the magnetic phase transition temperature as well as the low-temperature magnetic hyperfine field decrease with increasing unit cell volume.

Determination of the electric field gradient and the magnetic field in M\xf6ssbauer spectroscopy

Problem of unambiguous determination of all components of the electric field gradient and hyperfine magnetic field in case of mixed hyperfine interaction was solved for the first time. Concept of a new method to determine orientation of hyperfine fields in the absorber Cartesian frame for Mössbauer spectroscopy for nuclear transitions between levels with spin 3/2 and 1/2 is presented. The method can be applied for single-crystal absorbers with well separated absorption lines in their spectra. Explicit formulas derived from velocity moments are presented. The new method allows full separation of the electric quadrupolar and magnetic dipolar hyperfine interactions by using unpolarized radiation.

Coexistence of superconductivity and magnetism in CaK(Fe1−xNix)4As4 as probed by 57Fe Mössbauer spectroscopy

Temperature dependent $^{57}$Fe M\"ossbauer spectroscopy and specific heat measurements for CaK(Fe$_{1-x}$Ni$_x$)$_4$As$_4$ with $x$ = 0, 0.017, 0.033, and 0.049 are presented. No magnetic hyperfine field (e.g. no static magnetic order) down to 5.5 K was detected for $x$ = 0 and 0.017 in agreement with the absence of any additional feature below superconducting transition temperature, $T_c$, in the specific heat data. The evolution of magnetic hyperfine field with temperature was studied for $x$ = 0.033 and 0.049. The long-range magnetic order in these two compounds coexists with superconductivity. The magnetic hyperfine field, $B_{hf}$, (ordered magnetic moment) below $T_c$ in CaK(Fe$_{0.967}$Ni$_{0.033}$)$_4$As$_4$ is continuously suppressed with the developing superconducting order parameter. The $B_{hf}(T)$ data for CaK(Fe$_{0.967}$Ni$_{0.033}$)$_4$As$_4$, and CaK(Fe$_{0.951}$Ni$_{0.049}$)$_4$As$_4$ can be described reasonably well by Machida's model for coexistence of itinerant spin density wave magnetism and superconductivity [K. Machida, J. Phys. Soc. Jpn. {\bf 50}, 2195 (1981)]. We demonstrate directly that superconductivity suppresses the spin density wave order parameter if the conditions are right, in agreement with the theoretical analysis.

Ab initio study of the role of defects on the magnetic response and the structural, electronic and hyperfine properties of ZnFe2O4

In this work the effects of defects (oxygen vacancies, cationic inversion) on the structural, electronic and the magnetic response of the spinel ZnFe2O4 (ZFO) are studied by using a density functional theory (DFT) based ab initio method (the Full-Potential Linearized Augmented Plane Waves plus Local Orbitals, LAPW+lo) on the framework of the Generalized Gradient Approximation plus U (GGA+U) level. The changes induced by the defects in the hyperfine interactions at the Fe sites of the structure are also presented. In order to discuss the magnetic ordering and the electronic structure of the system we considered different spin arrangements. We found that, similar to the normal and pristine case, reduced and partially inverted ZFO presents an energy landscape characterized by a large number of metastable states. Our calculations successfully describe the hyperfine properties (isomer shift, magnetic hyperfine field and quadrupole splitting) at the Fe sites that are seen by Mössbauer Spectrocopy (MS) at 4 and 300 K, enabling us to characterize the local structure around Fe atoms. Our LAPW+lo predictions also demonstrate the relevance of both oxygen vacancies and antisites (cationic inversion) in the formation of local ferromagnetic coupling between Fe ions, giving rise to a ferrimagnetic ordering in an otherwise antiferromagnetic compound. This results support conclusions based in experimental results obtained in x-ray magnetic circular dichroism and magnetization measurements performed on zinc ferrites with different cation distributions and oxygen vacancy concentrations reported in the literature.

Structural and Magnetic Studies of Cr3+ Substituted Nickel Ferrite Nanomaterials Prepared by Sol-Gel Auto-Combustion

The present study envisages the preparation of chromium substituted Nickel ferrite NiCrxFe2−xO4 (x = 0~1.0) powders by a sol-gel auto-combustion method. X-ray diffraction analysis (XRD) showed that the specimens with x &gt; 0.2 exhibited a single-phase spinel structure, and that more content of Cr within a specimen is favorable for the synthesis of pure Ni-Cr ferrites. The lattice parameter decreased with an increase in the Cr concentration. The sample without calcining exhibited a good crystallinity. Scanning Electron Microscopy (SEM) showed the formation of ferrite powders nano-particles, and that the substitution of Cr weakened the agglomeration between the particles. Mössbauer spectra of NiCrxFe2−xO4 showed two normal Zeeman-split sextets that displayed a ferrimagnetic behavior. Furthermore, the spectra indicated that iron was in the Fe3+ state, and the magnetic hyperfine field at the tetrahedral tended to decrease with an increase in the Cr substitution. The saturation magnetization decreased by the Cr3+ ions, and reached a minimum value (Ms = 4.46 emu/g). With an increase in the annealing temperature, the coercivity increased initially, which later decreased.

Investigation of spin-orientation in antiferromagnetic ordering for LiFe1-xZnxPO4 with Mössbauer spectroscopy

We have investigated the spin orientation in antiferromagnetic polycrystalline LiFe1-xZnxPO4 using Mössbauer spectroscopy. The temperature-dependent magnetic susceptibility curves show antiferromagnetic behavior with ordering temperature. The experimentally determined effective moment of LiFe1-xZnxPO4 is larger than the theoretical value, which can be explained as incomplete absence of orbital contribution by the crystalline field around distorted octahedra. The value of the Néel temperature (TN) and the spin reorientation temperature (TS) of LiFe1-xZnxPO4 decreased with the increasing Zn concentrations from 48 and 14 K for x = 0.1 to 36 and 8 K for x = 0.5, resulting in weak antiferromagnetic interaction. Below TN, Mössbauer spectra of LiFe1-xZnxPO4 showed asymmetric eight-line shape due to the strong crystalline field in the distorted octahedral structure. A change in both the magnetic hyperfine field and electric quadrupole splitting below TS suggests that magnetic phase transition is related to the spin rotation and the superexchange interaction.

Magnetic properties of mixed sodium-lithium iron fluorophosphate NaLiFePO4F cathode material

Mixed sodium-lithium iron fluorophosphates NaLiFePO4F was synthesized by solid-state route. The crystal and magnetic properties were investigated by X-ray diffraction (XRD) measurement, vibrating sample magnetometer (VSM), and Mössbauer spectroscopy. The crystal structure of NaLiFePO4F was determined to be orthorhombic with space group of Pnma. The cell parameters of NaLiFePO4F are as follows: a0 = 10.9661 Å, b0 = 6.3693 Å, c0 = 11.4342 Å, and V = 798.6377 Å3. The temperature-dependence of the zero-field-cooled (ZFC) and field-cooled (FC) curves was examined by VSM at 100 Oe from 4.2 to 295 K. We determined the Néel temperature (TN = 22 K) and spin reorientation temperature (TS = 13 K). The Mössbauer spectra of NaLiFePO4F were taken at various temperatures ranging from 4.2 to 295 K. At below TS, the electric quadrupole splitting (ΔEQ) decreased and magnetic hyperfine field (Hhf) increased with decrease temperature due to spin-orbit coupling.