Hyperfine magnetic fields in substituted Finemet alloys

Transmission Mössbauer spectroscopy was used to determine the hyperfine fields of Finemet-type alloys in form of ribbons, substituted alternatively by Mn, Ni, Co, Al, Zn, V or Ge of various concentration. The comparative analysis of magnetic hyperfine fields was carried out which enabled to understand the role of added elements in as-quenched as well as annealed samples. Moreover, the influence of the substitution on the mean direction of the local hyperfine magnetic field was examined.     

Static and dynamic hyperfine interactions of Mn and Co impurities in the weak ferromagnet ZrZn2

We report the nuclear orientation of near-stoichiometric samples of ZrZn₂ containing trace impurities of radioactive⁵⁴Mn and⁶⁰Co in the temperature range 6.5–60 mK and in applied fields between 0.2 and 5.7 T. Analysis of the resullts indicates that in both cases, the transition-element impurities occupy two sites (the Zr and Zn sites) with about equal probablities. In one site, most probably that of Zr, both impurities have positive hyperfine fields of +12.0 T and +3.8 T for Mn and Co, respectively; in the other site, the corresponding hyperfine fields are negative, with the values −6.0 T and −6.9 T. The dynamic hyperfine interaction of Mn in ZrZn₂ has also been studied using the thermal cyclic method with a weak thermal link, and was analyzed for the two relaxation times corresponding to the different lattice sites.     

Conversion electron Mössbauer spectroscopic study of YIG substituted with Bi,Ti, Ga and La

YIG films, substituted with Bi, Ti, Ga and La, were grown on a (111) plane of Gd₃Ga₅O₁₂ or (Gd, Ca)₃(Ga, Mg, Zr)₅O₁₂ by a liquid phase epitaxial method. With the increase of the concentration of Bi atoms, which are substituted at 24c sites of YIG, the magnetic hyperfine fields at 16a and 24d Fe sites increased and the direction of magnetic moments changed from parallel to 45° to the (111) plane. With the increase of Ga concentration, the hyperfine fields at 16a and 24d Fe sites decreased. The hyperfine interaction and the substitution effect of YIG films are discussed.     

Changes in structure and magnetic hyperfine fields of Finemet alloys, induced by transition elements substitution

Amorphous as well as two-phase nanocrystalline Finemet-type soft magnetic alloys substituted by transition elements (Ni, Co, V) have been studied by means of Mössbauer spectroscopy. The main subject of interest was the distribution of magnetic hyperfine field (MHF) in Ni substituted alloys. The increase of mean MHF was stated as a result of crystallization. It was found that changes of transition metal concentration cause different kind of hyperfine field evolution, attributed both to the alteration in grain structure and other effects related to crystallization processes.     

Crystallinity and magnetic properties of electrodeposited Co nanowires in porous alumina

Crystalline Co nanowires were pulse electrodeposited into nanoporous aluminum oxide template having an ultra-thinned barrier layer. The effects of off-time between pulses and electrolyte acidity on the microstructure and magnetic properties of the nanowires were investigated. Increasing the off time between pulses increased the crystallinity and the alignment of easy axis with the wire axis. The rate of these increments was seen to depend on the electrolyte acidity and reached its maximum at pH=5.25 electrolyte acidity. Optimizing the crystallinity and crystal orientation, a coercivity value of 3320 Oe and a squareness of>90% were obtained for pure Co nanowires. A 10% increase in coercivity was found after annealing the samples.     

Doping effects of transition metals on the superconductivity of (Li,Fe)OHFeSe films

The doping effects of transition metals(TMs = Mn, Co, Ni, and Cu) on the superconducting critical parameters are investigated in the films of iron selenide(Li,Fe)OHFe Se. The samples are grown via a matrix-assisted hydrothermal epitaxy method. Among the TMs, the elements of Mn and Co adjacent to Fe are observed to be incorporated into the crystal lattice more easily. It is suggested that the doped TMs mainly occupy the iron sites of the intercalated(Li,Fe)OH layers rather than those of the superconducting Fe Se layers. We find that the critical current density J_c can be enhanced much more strongly by the Mn dopant than the other TMs, while the critical temperature T_c is weakly affected by the TM doping.     

Study of hyperfine interactions in pure and Co-doped CeO2 nanoparticles by PAC spectroscopy using 111Cd

In this work we have used the Perturbed Angular Correlation (PAC) technique to measure the hyperfine interactions in pure nanostructured (crystallite size around 70 nm) as well as doped with 3d transition metal Co (3 at. %) CeO₂ samples. The PAC measurements were performed at different temperatures between 23 and 527°C. The results did not reveal any evidence of hyperfine magnetic interactions. Spectra obtained presented three major frequencies related to substitutional sites in CeO₂, grain boundary sites and intrinsic defect related sites.     

M?ssbauer investigations of crystalline and quasicrystalline Al3(Mn, Fe) compounds

(57)Fe M?ssbauer and magnetic measurements are reported on Taylor phase compounds T-Al(3)(Mn,Fe), which can be seen as complex metallic alloys. The orthorhombic unit cell contains 156 atoms. These investigations are further extended to Al(71)Mn(19)Fe(10) crystallizing as a decagonal quasicrystal. Common to both structures are layers, which are oriented perpendicular to the b axis in the crystalline or to the periodic axis in the quasicrystalline compound, allowing the formation of characteristic building blocks. At low temperatures for all samples spin glass behavior is observed with freezing temperatures T(f) increasing with Fe content. Above T(f) the (57)Fe M?ssbauer spectra were analyzed by a superposition of two subspectra with intensity ratio around 75:25, which can be allocated to Fe substituted on Mn sites surrounded either by Al and Mn or solely by Al with Mn only at the edge of the nearest neighbor shell. For both subspectra quadrupole splitting and center shift do not change significantly with Fe content and with structure. Below T(f) broad hyperfine field distributions with non-vanishing contributions at zero hyperfine field are present. Magnetic and electrostatic hyperfine interactions are governed by length scales which are determined by the very similar interatomic configurations forming the T-Al(3)Mn phase as well as the decagonal compound. The presence of long range atomic order is of less importance.     

Mössbauer study of the modified pyrochlores CsMFeF6 (M = Mn,Ni)

⁵⁷Fe Mössbauer spectra of the modified pyrochlores CsMFeF₆ (M = Mn, Ni) were obtained between 1.5 K and room temperature. The spectra for single crystal and powder absorbers are very similar, and demonstrate the randomness associated with the iron sites. Nevertheless, the presence of two distinct iron sites, recently reported by Varret and Courbion for powder samples, is confirmed. Both CsMnFeF₆ and CsNiFeF₆ are antiferromagnets with Néel temperatures, T_N, of 25 and 5.2 K, respectively. The hyperfine fields lie on the Brillouin function with $\text{S =}\text{5}\text{2}$. The hyperfine parameters show that the iron ions are ferric in the high-spin state.     

Transferred hyperfine fields at 119Sn in Fe1−xMxSn [M≡Mn, Co and Ni]

The transferred hyperfine fields at ¹¹⁹Sn, using Mössbauer spectroscopy are reported for the hexagonal B-35 compounds with a general formula Fe_1?xM_xSn, where MMn, Co and Ni. In these compounds, Sn atoms occupy two crystallographically inequivalent sites. For FeSn the observed spectrum consists of a quadrupole doublet and a magnetic pattern corresponding to 2(d) and 2(a) sites respectively. The data have been analysed to resolve the controversy regarding hyperfine parameters. On replacing Fe by Mn atoms, additional lines appear in the higher velocity region of the Mössbauer spectrum and the intensity of the nuclear Zeeman pattern increases at the expense of quadrupole doublet. The resulting Mössbauer spectra have been analysed by taking only the nearest neighbour interactions into account. This analysis shows that on replacing each Fe atom by a Mn atom, the hyperfine field at 1(a) Sn site increases by about 40 kOe and a field of about 35 kOe is produced at the 2(d) Sn sites. Further, from the nuclear Zeeman pattern for 2(d) sites, the sign of quadropole splitting for these sites could also be determined and was found to be positive. However, the substitution of Co and Ni in place of Fe atoms results in a broad unresolved pattern suggesting that the hyperfine field at the 1(a) sites decreases and a finite field develops at the 2(d) site. The origin of transferred hyperfine fields at the two inequivalent Sn sites is discussed, the magnetic transition temperatures of these compounds have been estimated and the magnetic moments of M-atoms have been inferred.     

Mössbauer spectroscopy with high velocity resolution in the study of ordinary chondrites

Mössbauer spectroscopy with high velocity resolution was used to study of 11 ordinary chondrites from L and H chemical groups. Mössbauer spectra were recorded in 4,096 channels and then presented in 1,024 channels. An increase of velocity resolution allowed us to carry out more detailed analysis of ordinary chondrites and to decrease experimental error for evaluation of hyperfine parameters in comparison with previous chondrite Mössbauer spectra measured in 512 channels or less. Variations of hyperfine parameters were observed for corresponding iron bearing phases in chondrites. Two crystallographically non-equivalent octahedral sites M1 and M2 in olivine and pyroxene were revealed in Mössbauer spectra of bulk chondrite samples.     

Magnetism of (Fe0.93Ni0.07)2P studied using 57Fe Mössbauer spectroscopy

⁵⁷Fe Mössbauer spectroscopic measurements have been carried out on (Fe_0.93Ni_0.07)₂P in the temperature range 85–405 K. Obtained values of hyperfine field at the two metallic sites are slightly smaller than in Fe₂P. But the reduction is much less than as reported in Cr or Mn or Co substituted analogues of Fe₂P.     

Influence of substrate temperature and Cobalt concentration on structural and optical properties of ZnO thin films prepared by Ultrasonic spray technique

Pure and Cobalt doped zinc oxide were deposited on glass substrate by Ultrasonic spray method. Zinc acetate dehydrate, Cobalt chloride, 4-methoxyethanol and monoethanolamine were used as a starting materials, dopant source, solvent and stabilizer, respectively. The ZnO samples and ZnO:Co with Cobalt concentration of 2 wt.% were deposited at 300, 350 and 400 °C. The effects of substrate temperature and presence of Co as doping element on the structural, electrical and optical properties were examined. Both pure and Co doped ZnO samples are (0 0 2) preferentially oriented. The X-ray diffraction results indicate that the samples have polycrystalline nature and hexagonal wurtzite structure with the maximum average crystallite size of ZnO and ZnO:Co were 33.28 and 55.46 nm. An increase in the substrate temperature and presence doping the crystallinity of the thin films increased. The optical transmittance spectra showed transmittance higher than 80% within the visible wavelength region. The band gap energy of the thin films increased after doping from 3.25 to 3.36 eV at 350 °C.     

XRD,magnetic and Mössbauer spectral studies of nano size aluminum substituted cobalt ferrites (CoAlxFe2−xO4)

Aluminum substituted cobalt ferrites having particle size ∼10 nm were prepared using aerosol route, which increases with annealing temperature. The unit cell parameter ‘a’ and saturation magnetization decreases linearly with the increase of aluminum concentration. This is due to the smaller ionic radius and the diamagnetic nature of the Al³⁺, respectively. Room temperature Mössbauer spectra of the samples annealed at 1200 °C show broad sextets, which were fitted with different sextets, indicating different local environment of both tetrahedrally and octahedrally coordinated iron cation. Further, hyperfine field of the samples decreases with the increase of Al³⁺ concentration due to the fact that the Al³⁺ diamagnetic species reduce the magnetic interactions. Cations distribution indicated a increase in Fe³⁺(oct.)/Fe³⁺(tet.) ratio on increasing the Al³⁺ concentration.     

Formation of Mn-doped iron silicides by ball milling

Using X-ray diffraction (XRD) and Mössbauer spectroscopy, we have studied the sequence of phase formations in the solid Mn-doped iron silicide series Fe_1?x Mn _x Si₂, with 0.00? ≤ ?x? ≤? 0.12, in samples prepared by mechanical alloying from the pure elements. The milling was carried out at room temperature in Ar atmosphere in a horizontal mill for 15 h. The XRD patterns display broad lines, which can be ascribed to stable and metastable iron silicides like β-FeSi₂, ?-FeSi, α-FeSi₂, MnSi, and Si. The set of hyperfine parameters obtained support the coexistence of β-FeSi₂, α-FeSi₂ and ?-FeSi, in agreement with the XRD results. No replacement of Fe by Mn atoms in the regular sites of β-FeSi₂ has been observed.     

A Mössbauer spectral study of the Jilin meteorite

The iron57 Mössbauer spectra of three different samples of the Jilin meteorite have been measured at 78 and 295 K. Five iron containing major components are identified, two magnetic components, kamacite and troilite, and three nonmagnetic components, olivine, pyroxene, and an iron(III) component. The relative absorption areas of these five components show that sample A contains a larger fraction of magnetic components, ca. 50 percent, than samples B and C, which contain ca. 30 percent. This difference indicates a significant compositional inhomogeneity in the Jilin meteorite. The fit of the troilite component sextet is extensively discussed in the paper and requires the adjustment of not only the isomer shift and hyperfine field, but also of the quadrupole interaction, the asymmetry parameter of the electric field gradient tensor, and the orientation of the hyperfine field in the principal axes of the electric field gradient tensor. The smaller isomer shift and hyperfine field of the kamacite mineral in sample B indicate that this sample contains less nickel than the kamacite in samples A and C, in which the amount of nickel is estimated to be ca. 9 percent. On the basis of its hyperfine parameters, the iron(III) component is assigned to iron(III) substituted on the M1 site of pyroxene.     

Influence of Mn-for-Fe substitution on structural properties of synthetic goethite

In order to study the effect of alloying elements, such as manganese, on the properties of the rust on weathering steels, a series of Mn-goethite samples containing different amounts of Mn were synthesized from ferrihydrite in alkaline media. The samples were characterized by X-ray diffraction (XRD) and Mössbauer spectroscopy. The cell parameters calculated from the XRD patterns showed clearly that the a- and c-parameters decrease while the b-parameter increases with increasing Mn concentration, indicating that the octahedra of the goethite structure become distorted by an incorporation of Mn (Jahn–Teller-effect). Mössbauer spectra of the samples were recorded at room temperature (RT) and at 80 K. The quadrupole shift values gradually decrease with increasing Mn substitution in the goethite structure. It has been observed that the magnetic hyperfine field values of maximum probability are reduced with increasing Mn in the samples. No doublet component was observed in the RT MS spectra suggesting that no effects of superparamagnetim resulting from smaller particles are present.     

ESR在ACEL ZnS:Mn,Cu和ZnS:Cu材料研究中的应用

ZnS:Mn,Cu粉末发光材料的ESR谱随Mn2+浓度和制备条件的不同有着明显的变化。根据耦合Mn2+的ESR谱理论分析,计算ESR谱参数及其饱和现象表明,当Mn2+浓度>0.2%,Mn2+开始形成离子团,Mn2+团的形成和Mn2+离子与晶格间耦合随Mn2+浓度的增大而增强是发光浓度猝灭的主要原因,Mn2+浓度约为0.7%具有最高发光亮度。本文还讨论了退火条件对ZnS:Mn,Cu ESR谱的影响以及老化的ZnS:Cu中Cu2+的ESR谱。     

Magnetic hyperfine fields at Ta in Co and Fe hosts measured by the e−-γ time-differential perturbedangular-correlation method

The radioactivity¹⁸¹Hf was implanted into pure Co and Fe hosts with the help of an isotope separator. The ferromagnetic hosts produce very strong magnetic hyperfine interactions at the nuclear site of Ta atoms. These hyperfine interactions were studied by time-differential measurements of the 133 keV conversion electron — 482 keV γ angular correlation. It is found that in both hosts an appreciable fraction of Hf atoms occupies regular lattice sites after the implantation. Using the knowng-factor of the 482 keV state of¹⁸¹Ta the magnetic hyperfine fieldsH _hf=±362.4(5.0) and ±596(18) kG for the Co and Fe hosts, respectively, were deduced These fields fit nicely into the systematics of the hyperfine fields for the 5d transition elements but are not well accounted by the existing theoretical models.     

57Fe Mössbauer study of Li x Fe1-y Co y PO4 (y = 0, 0.1, 0.2) as cathode material for Li-ion batteries

Lithium iron phosphates LiFe_1-y Co _y PO₄ (y = 0, 0.1, 0.2) exposed to a charging process were studied by ⁵⁷Fe Mössbauer spectroscopy taking into account XRD and SEM data. Hyperfine parameters of the spectra were determined above and below the magnetic ordering temperature for all the samples. It was shown that the presence of Co impurity atoms in lithium phosphates gives no effect on the hyperfine interaction of ⁵⁷Fe²⁺ cations. However, Co atoms in the nearest cation environment of Fe atoms lead to a significant change of the hyperfine interactions of ⁵⁷Fe³⁺ cations. The Co impurity atoms distribution over the positions of the iron atoms in the structure is found not to be statistical,but correlated.