Hyperfine Field Research Articles

Epitaxial Co1-xMox thin film alloys studied by 59Co NMR

59Co NMR (Nuclear Magnetic Resonance) has been used to investigate the distribution of 59Co hyperfine fields in the Co1-xMox thin film alloys (0.01 < x < 0.1) co-deposited on V buffer. At x = 0 the films consisted of a mixture of fcc and hcp Co, and Mo was found to enter randomly the two Co fractions in the investigated concentration range. However, alloying with Mo was found to increase the amount of stacking faults, in agreement with the previously published results of theoretical calculations for binary alloys. A certain deviation from a random distribution of Mo, most probably due to the presence of magnetically induced miscibility gap for Co:Mo, has been identified for the alloys with Mo content larger than 1%. It was found that in the limit of a very small Mo concentration x ≈ 0, each Mo nearest neighbor lowers the 59Co NMR resonance frequency by 43.8 MHz, i.e. the corresponding hyperfine field is reduced by 4.34 T, implying that Co atoms would become nonmagnetic when 5 Mo atoms enter as the nearest neighbors. However, the effect increases with concentration, due to the contribution from Mo in the more distant shells. The extrapolation to Mo concentration higher than the one used in the experiment predicts that Co becomes nonmagnetic when surrounded by 3 Mo nearest neighbors for the concentration as low as x = 0.2–0.25.

Study of hyperthermia temperature of manganese-substituted cobalt nano ferrites prepared by chemical co-precipitation method for biomedical application

Abstract The initiation of ferrite nanoparticles has changed the perception of nanotechnology in the biomedical field especially magnetic hyperthermia based application. Wet chemical co-precipitation method has been used to synthesize chitosan-coated Co1−xMnxFe2O4 (0.0 ≤ x ≤ 1.0, in the steps of 0.2) nano ferrites. From the XRD data, the lattice constant, ionic radii and bond lengths at tetrahedral sites and octahedral sites were estimated. The analysis revealed that the hoping lengths at tetrahedral and octahedral sites are increased with the addition of manganese content. The FESEM has shown that the ferrite nanoparticles are agglomerated in the powder sample. The magnetic characterization has been done by VSM. Heating of the nanoparticles is dependent on hysteresis loss that is related to the larger area of the hysteresis loop. In agreement with magnetization data, there shows a transition from ferromagnetic to paramagnetic behaviour revealed by Mossbauer spectra. From Mossbauer spectra, values of isomer shift, quadrupole splitting, and hyperfine field have been measured. Hydrodynamic diameter and polydispersity index (PDI) of all coated samples have been found in the limits that the samples can be used for biomedical applications. Hyperthermia temperatures of all coated ferrite samples have been measured. From the steep slope of time dependence temperature graph, the value of specific loss power (SLP) has been calculated and found that the SLP value is highest for Co0.8Mn0.2Fe2O4.

Estimation of structural composition of the inverse spinel ferrites using 57Fe-Zero Field Nuclear Magnetic Resonance

We have demonstrated 57Fe Zero Field Nuclear Magnetic Resonance (ZFNMR) as a powerful tool in determining the structural composition of nickel-cadmium spinel ferrites of various compositions of Ni1-x Cdx Fe2O4 from x = 0 to1, which are synthesized via one-step auto combustion technique. The XRD measurements confirm the phase purity of all the samples. Vibrating Sample Magnetometry (VSM) measurements show that saturation magnetization (MS) increases initially (up to x = 0.3) and then decreases for higher concentrations of cadmium. The Fe3+ ions in the inverted spinel ferrite distribute equally among two possible sites (tetrahedral A and octahedral B) with different hyperfine fields. Therefore for x = 0 under the assumption that Ni enters B sites, 57Fe NMR of Fe3+ ions yield two signals of equal integral intensities in spectral lines corresponding to these sites. Thus, for the sample series Ni1-x Cdx Fe2O4, the contribution of Fe3+ nuclei varies for A and B sub-spectra with the substitution of a non-magnetic Cd2+ ion. By measuring the Fe3+ distribution on A and B sites which is determined from relative spectral areas of A and B NMR sub-spectra the cation distribution is estimated and has been verified by the binomial distribution. Further, XRD Rietveld refinement results are also in good agreement with the composition estimated by NMR technique and the ideal composition. We have demonstrated the usefulness of NMR technique to quantify the accurate composition of the mixed spinel ferrite systems using Ni-Cd ferrite as a test case. Further, the estimated inversion parameter (at around x = 0.4), for the studied system, obtained from ZFNMR, XRD, and VSM techniques are in excellent agreement with each other.

Ferromagnetic Nanoregions in Cubic Sr0.98La0.02MnO3 Manganite According to 139La NMR Data

It is shown that 139La nuclear magnetic resonance data indicate that ferromagnetic regions are formed near La ions in cubic Sr0.98La0.02MnO3 manganite. Part of the La ions remain in the antiferromagnetic matrix having a canted structure. The orbital and spin contributions to the shift of the 139La nuclear magnetic resonance line, as well as the induced hyperfine fields, are determined.

DFT and Mössbauer Spectroscopy Study of a FeTe0.5Se0.5 Single Crystal

The iron based superconductor FeSe0.5Te0.5 has been studied applying Mossbauer spectroscopy and ab initio density functional theory calculations of hyperfine parameters of iron nuclei. It has been shown that the presence of interstitial iron atoms leads to dividing of iron atoms in the compound into three groups with different hyperfine parameters. The experimental room-temperature Mossbauer spectrum has been well described within a three-group model, based on the results of ab initio calculations. The low-temperature Mossbauer spectrum has been described by a set of magnetic sextets, characterized by a distribution of hyperfine fields on 57Fe nuclei. The latter is compatible with an incommensurate spin-density wave phase, which coexists with superconductivity as it was observed also in other iron-based superconductors.

Detailed physical property characterization of FeTe1−xSex (0.00 ≤ x ≤ 0.50) single crystals

Here, we report self flux single crystal growth of FeTe1−xSex (0.00 ≤ x ≤ 0.50) series via solid state reaction route; the resulted crystals as seen are shiny. X-Ray diffraction (XRD) performed on the surface of crystals elucidated the growth in (00l) plane, i.e. orientation in c-direction only. Scanning electron microscopy (SEM) images showed slab like morphology and EDX (Energy dispersive x-ray analyzer) confirmed that the crystals are closed to their designed compositions. Rietveld analysis of the XRD patterns of crushed crystal powders showed that the cell parameters decrease with Se content increase. Coupled magnetic/structural phase transition temperature, seen as a step in resistivity for the lower Se concentration i.e. 0.00 ≤ x ≤ 0.07, decreases from around 65 K for x = 0.0 to 50 K for x = 0.07 and it is not detected for higher x values. Superconductivity is observed by resistivity measurement for higher Se concentration i.e. 0.07 ≤ x ≤ 0.50, up to a maximum temperature of 14 K at x = 0.50. Thermally Activated Flux Flow (TAFF) analysis based on high field transport measurements in superconducting region done for x = 0.20 crystal exhibited activated flux energy to be decreasing from 12 meV (0.5Tesla) to 4.6 meV (14Tesla). Raman spectroscopy at room temperature of synthesized samples exhibits all the allowed phonon modes with slight shift to higher frequency with Se content. Mossbauer spectra of FeTe1−xSex crystals series were recorded at 300 and 5 K. At 5 K, the average hyperfine field decreases systematically with Se content increase from 10.6 to 6.1Tesla for x = 0.0 to x = 0.20 samples. This indicates a possibility of co-existing magnetism and superconductivity in 0.07 ≤ x ≤ 0.20 crystals. For x = 0.50 sample, no hyperfine field related to magnetic ordering is seen. Based on above results, detailed phase diagram of the FeTe1−xSex (0.00 ≤ x ≤ 0.50) compounds is defined in the present study.

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.

Structure and Magnetic Properties of Bulk Synthesized Mn2−xFexP1−ySiy Compounds from Magnetization, 57Fe Mössbauer Spectroscopy, and Electronic Structure Calculations

The series of Mn2−xFexP1−ySiy types of compounds form one of the most promising families of magnetocaloric materials in term of performances and availability of the elemental components. Potential for large scale application needs to optimize the synthesis process, and an easy and rather fast process here described is based on the use of two main type of precursors, providing the Fe-P and Mn-Si proportions. The series of Mn2−xFexP1−ySiy compounds were synthesized and carefully investigated for their crystal structure versus temperature and compared interestingly with earlier results. A strong magnetoelastic effect accompanying the 1st order magnetic transition—as well as the parent phosphide–arsenides—was related to the relative stability of both the Fe magnetic polarization and the Fe–Fe exchange couplings. In order to better understand this effect, we propose a local distortion index of the non-metal tetrahedron hosting Fe atoms. Besides, from Mn-rich (Si-rich) to Fe-rich (P-rich) compositions, it is shown that the magnetocaloric phenomenon can be established on demand below and above room temperature. Excellent performance compounds were realized in terms of magnetic entropy ΔSm and adiabatic temperature ΔTad variations. Since from literature it was seen that the magnetic performances are very sensitive to the synthesis process, correspondingly here a new effective process is proposed. Mössbauer spectroscopy analysis was performed on Mn-rich, equi-atomic Mn-Fe, and Fe-rich compounds, allowing determination of the distribution of hyperfine fields setting on Fe in the tetrahedral and pyramidal sites, respectively. Electronic structure calculations confirmed the scheme of metal and non-metal preferential ordering, respectively. Moreover, the local magnetic moments were derived, in fair agreement with both the experimental magnetization and the Fe contributions, as determined by Mössbauer spectroscopy.

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.

Thermal annealing effects on the structural, magnetic and hyperfine properties of the Fe/SnO2/Fe thin film deposited by RF sputtering method

In the present work, the effect of the post-deposition annealing process in an air atmosphere on the structural and magnetic properties of the ternary Fe/SnO2/Fe thin film, deposited by the sputtering technique was reported. X-ray diffraction (XRD) pattern confirms the formation of alpha-iron, magnetite and tin dioxide phases in the as-deposited film. Meanwhile, after the thermal annealing, the formation of hematite and tin dioxide phases was determined. Magnetization (M) measurements reveal some features after the annealing: i) a reduction of the coercive field (HC), which has been assigned to the presence of hematite, and ii) the transformation of alpha-iron/magnetite phases into the hematite phase in accordance with results obtained from XRD data analysis. Those results were also confirmed by room temperature Conversion electron Mössbauer spectroscopy (CEMS) measurements carried out using a 57Co(Rh) source. Furthermore, the doublets of the CEMS spectrum of the as-deposited film (21%) has been assigned to the signal of Fe3+ and Fe2.5+ (mixture of Fe3+ and Fe2+) ions, which diffuse into the SnO2 matrix. The spectral area of those doublets is clearly reduced to 3% after the thermal annealing. It suggests the migration of the Fe ions from the non-magnetic phase to the magnetic phase. On the other hand, CEMS spectrum of the as-deposited film carried out with using a 119 mSn source is well modeled with a doublet and a sextet. The doublet was assigned to Sn4+ ions of the SnO2 phase; meanwhile, the sextet was assigned to Sn4+ ions located at interstitial and/or substitutional sites of the alpha-iron/magnetite phases. Those tin ions sense the supertransferred hyperfine field from Fe neighbor. After the thermal annealing, the CEMS spectrum was well modeled with only a doublet related to SnO2 phase, suggesting that the tin ions have been out diffused from the magnetic phase (alpha-iron and magnetite) and incorporate into the no magnetic o-SnO2.

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.

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

Magnetically tunable organic semiconductors with superparamagnetic nanoparticles

Effects of hyperfine fields, BN, and induced fields, BI, from superparamagnetic nanoparticles on the spin mixing in organic semiconductors.

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.

Coherence Properties of Shallow Donor Qubits in ZnO

Defects in crystals are leading candidates for photon-based quantum technologies, but progress in developing practical devices critically depends on improving defect optical and spin properties. Motivated by this need, we study a new defect qubit candidate, the shallow donor in ZnO. We demonstrate all-optical control of the electron spin state of the donor qubits and measure the spin coherence properties. We find a longitudinal relaxation time T$_1$ exceeding 100 ms, an inhomogeneous dephasing time T$_2^*$ of $17\pm2$ ns, and a Hahn spin-echo time T$_2$ of $50\pm13$ $\mu$s. The magnitude of T$_2^*$ is consistent with the inhomogeneity of the nuclear hyperfine field in natural ZnO. Possible mechanisms limiting T$_2$ include instantaneous diffusion and nuclear spin diffusion (spectral diffusion). These results are comparable to the phosphorous donor system in natural silicon, suggesting that with isotope and chemical purification long qubit coherence times can be obtained for donor spins in a direct band gap semiconductor. This work motivates further research on high-purity material growth, quantum device fabrication, and high-fidelity control of the donor:ZnO system for quantum technologies.

Influences of element segregation on the magnetic properties in nanocrystalline Nd-Ce-Fe-B alloys

The RE-rich (Ce1−xNdx)16Fe78B6 (x = 0–1) nanocrystalline alloys were prepared by melt-spinning method. The transmission electron microscopy equipped with EDS was employed to investigate the microstructure and rare-earth element segregation. The average Nd/RE ratios in 2:14:1 grains are 22, 52, 67, 74, 78, and 81% for the x = 0.1, 0.4, 0.5, 0.6, 0.7, and 0.8 alloys, respectively, which are larger than the nominal ratios, indicating a Nd segregation in 2:14:1 phase. The Nd/RE ratio changing with x shows a two-stage of increment: the average increment in x = 0.1–0.5 alloys is much higher than that of x = 0.5–0.8 alloys. The corresponding change is also observed in the plotted intrinsic parameters of cell volume V, hyperfine field Bhf, and spin reorientation temperature TSR of the 2:14:1 phase changing with x curves. The high Ce-contained RE-rich Nd-Ce-Fe-B with strong element segregation shows high coercivities and high performance/price ratio. The present results thus contribute to understanding the fundamental mechanism of Ce-contained Nd-Ce-Fe-B permanent magnets and taking advantage of the element segregation.

Tuning effective hyperfine fields in PEDOT:PSS thin films by doping

Using electrically detected magnetic resonance spectroscopy, we demonstrate that doping the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) with ethylene glycol allows for the control of effective local charge carrier hyperfine fields through motional narrowing. These results suggest that doping of organic semiconductors could enable the tuning of macroscopic material properties dependent on hyperfine fields such as magnetoresistance, the magneto-optical responses and spin-diffusion.

Hyperfine interaction in cobalt by high-resolution neutron spectroscopy

We have investigated the ferromagnetic phase transition of elemental Co by high-resolution neutron backscattering spectroscopy. We monitored the splitting of the nuclear levels by the hyperfine field at the Co nucleus. The energy of this hyperfine splitting is identified as the order parameter of the ferromagnetic phase transition. By measuring the temperature dependence of the energy we determined the critical exponent and the ferromagnetic Curie temperature of K. The present result of the critical exponent agrees better with the predicted value (0.367) of the three-dimensional Heisenberg model than that determined previously by nuclear magnetic resonance.

Mössbauer Study and Curie Temperature Configuration on Sintering Nano-Ni-Zn Ferrite Powder

Variations of Curie temperature and strength of magnetic phases with sintering temperature and Ni concentration is investigated in the present work. The AC susceptibility studies show a decrease in Curie temperature (TC) with an increase in Ni concentration in the samples. Comparison of Curie temperatures with the reported results reveals that samples in the present work show higher TC enabling high thermal stability. The Mossbauer spectra of nano- and sintered Ni-Zn ferrite samples were recorded at room temperature to monitor the local environment around Fe cations through Mossbauer hyperfine parameters as a function of composition and sintering temperatures. The increase in sharpness of the Mossbauer sextet with an increase in Ni concentration and sintering temperature corroborate improvement in homogeneity and ferrimagnetic ordering. The results of hyperfine parameters offer the possibility of having close view on configuring Curie temperature through monitoring hyperfine field by altering sintering temperature and/or Ni concentration. As the temperature dependence of magnetic and magnetoelastic properties is strongly influenced by the Curie temperature, the successful possible configuration of Curie temperature in the present work can be further investigated for desired sensor applications.

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.