Mössbauer and Nuclear orientation study of magnetic atom behaviour in AuFe below the percolation threshold

An⁵⁷Fe Mössbauer study and⁶⁰Co and⁵⁴Mn nuclear orientation (NO) studies of the Au₈₆Fe₁₄ alloy have been performed. A transition to the spin glass state was observed below approximately 50 K. NO of the⁶⁰Co impurity showed absence of the polarization of the⁶⁰Co nuclei. For⁵⁴Mn impurities the dependence of the Mn effective magnetic field on external field andtemperature was found.     

Giant magnetic moments in dilute magnetic semiconductors

The concentration dependence of the specific magnetic moment value at room temperature in dilute semiconductor titanium oxides doped with either Co or Fe has been investigated. This value was found to increase sharply at small concentrations of magnetic impurity. The magnetic moment of 22.9 μ_B per impurity atom has been revealed for TiO₂ doped with 0.15 at% Co, not yet reported in any semiconductor oxide systems. We conclude the observed giant magnetic moments are caused by the crystal lattice polarization at small impurity concentrations. The comparison with published data point to different types of the magnetization concentration dependence for various semiconductor matrixes that is probably related to the dielectric permittivity of the environment.     

Superferromagnetic state of α-Fe in Fe implanted Co6Ag94 studied by Mössbauer spectroscopy

After having introduced by ion implantation ⁵⁷Fe to a local concentration of 7 at% into Co₆Ag₉₄, we observed it by conversion electron Mössbauer spectroscopy in the as-prepared state and after isochronal annealing. A superferromagnetic state is inferred, which is correlated with the ordering of the magnetic moments on the Fe clusters through chain-like or dendritic Co/Fe linear structures. The magnetic moment disordering temperature lies above 473 K.     

Mössbauer and XRD study of novel quaternary Sn-Fe-Co-Ni electroplated alloy

Constant current electrochemical deposition technique was used to obtain quaternary alloys of Sn-Fe-Co-Ni from a gluconate electrolyte, which to date have not been reported in the literature. For the characterization of electroplated alloys, ⁵⁷Fe and ¹¹⁹Sn Conversion Electron Mössbauer Spectroscopy (CEMS), XRD and SEM/EDAX were used. XRD revealed the amorphous character of the novel Sn-Fe-Co-Ni electrodeposited alloys. ⁵⁷Fe Mössbauer spectrum of quaternary deposit with composition of 37.0 at% Sn, 38.8 at% Fe, 16.8 at% Co and 7.4 at% Ni displayed a magnetically split sextet (B = 28.9T) with broad lines typical of iron bearing ferromagnetic amorphous alloys. Magnetically split ¹¹⁹Sn spectra reflecting a transferred hyperfine field (B = 2.3T) were also observed. New quaternary Sn-Fe-Co-Ni alloys were successfully prepared.     

Spin- and charge density perturbations and short-range order in Fe–Cu and Fe–Zn BCC alloys: A Mössbauer study

A model used to describe the ⁵⁷Fe Mössbauer spectra for the binary BCC iron alloys rich in iron has been extended to account for the alloy crystallographic ordering. The ordering is accounted for by introducing single order parameter. Extension of the model is described in detail. The model has been tested applying it to the Fe–Cu alloys obtained by the arc melting and to the Fe–Zn alloys prepared by the solid state reaction. Random alloys are obtained up to ∼2 at% of Cu, and up to ∼8 at% of Zn. For higher impurity (minor alloy component) concentration it has been found that Cu atoms try to avoid Fe atoms in the iron matrix as nearest neighbors, while the opposite happens to the Zn atoms, albeit at much lesser scale, i.e., Zn–Zn interactions are much weaker than Fe–Zn interactions at the nearest neighbor distance. Perturbations to the iron magnetic hyperfine field (spin density) and electron (charge) density on the iron nucleus have been obtained for both series of alloys versus impurity concentration.     

Recent experiments with transient NMRON

High resolution magnetic and electric hyperfine interaction distributions are determined for single crystal⁵⁴MnNi with diffused impurity concentrations of 0.14 and 0.40 at%, and for a 0.1 µm layer of⁶⁰CoFe co-plated onto single crystal Fe. High quality gamma detected nuclear spin echoes recorded for the⁶⁰CoFe specimen demonstrate that a reduced influence of the RF skin effect far outweighs any magnetic hyperfine field interaction broadening associated with the co-plating process.     

Mössbauer emission study of57Co: YBa2Cu3O7−y HTSC

Mössbauer emission spectroscopy is performed on⁵⁷Co:YBa₂Cu₃O_7–y oxides in a temperature range from 300 K to 77 K. The spectra show, at least two different location for the⁵⁷Co(⁵⁷Fe) impurities. The isomer shift and quadrupole splitting values of the⁵⁷Fe daughter are coincident with those observed in⁵⁷Fe absorption experiments. From the analysis of theIS andQS values as well as from the relative location of Fe impurity levels in the HTSC matrix it is argued that:a) Co impurities enters into the lattice mainly in the Cu1 sites, but some of them have a higher coordination number.b) The daughter⁵⁷Fe exists as localized Fe⁴⁺ state.c) The parent⁵⁷Co enter as a localized Co³⁺ state. These conclusions appear consistent with the observed increase ofN(0) on doping with Fe or Co ions and with the existence of localized magnetic moments as determined from paramagnetic susceptibility measurements.     

γ-Fe precipitation in melt-spunCuFe

The ribbon spinning method has been used to prepare samples containing enhanced fractions (∼ 3–6 at%) of iron precipitates in the fcc γ-phase fromCuFe alloys containing 5, 10 and 16 at% Fe. Details of the procedure, heat treatments and data analysis are presented. The behaviour of the intensity ratio parameter in applied field spectra (0–5.2 T) obtained below the antiferromagnetic ordering temperature of γ-Fe is also examined.     

Hyperfine fields and Mössbauer isomer shifts of 57Fe in PdAgFe alloys

The hyperfine fields B_hf and Mössbauer isomer shifts S of ⁵⁷Fe in two PdAgFe alloy series containing 3 and 7 at% have been measured at 4.2 K and 295 K. With increasing Ag content, a change in the magnetic ordering from ferromagnetism towards a spin-glass behaviour is indicated in the 3 at% Fe series.     

Hyperfine magnetic fields in Fe−Co alloys and their tempera ture dependences

We obtained⁵⁷Fe hyperfine field parameters from Fe₁−x-Co _x alloys (0≤x≤0.6) from 77 K to 900 K. We first discuss the origin of the low temperature hyperfine fields in terms of the 3d and 4s electrons at⁵⁷Fe atoms. The⁵⁷Fe hyperfine magnetic field (hmf) of Fe-Co alloys depends more weakly on temperature than the hmf of pure Fe. This temperature dependence occurs because the alignment of the magnetic moments at both the Fe atoms and at the Co atoms depend on temperature in the same way as the bulk magnetization of Fe-Co alloys.     

Growth behavior and magnetic property of electroless NiCoFeP films

The electroless NiCoFeP films were deposited on a silicon substrate in a bath containing Ni²⁺, Co²⁺, and Fe²⁺ ions with a concentration ratio of 1:1.9:1.2. These films were characterized by using transmission electron microscope, energy dispersive X-ray spectrometer, and alternating gradient magnetometer for their microstructure, crystal structure, and magnetic properties. The result showed that the film deposited at the initial stage (about 10 s) consists of only one phase with a crystal structure of FCC Ni and a composition about Ni (69 at%), Co (19 at%), Fe (4 at%), and P (7 at%); The film deposited at the latter stage (about 30 s) consists of two phase, one is similar to that of initial stage and the other has crystal structure of HCP Co with a composition about Ni (35 at%), Co (44 at%), Fe (19 at%), and P (2 at%). The saturation magnetization and coercivity of electroless NiCoFeP films vary from 525 to 1546 emu/cm³ [0.68–2.01 T] and from 51.44 to 88.5 Oe [4.09–7.04 kA/m], respectively.     

Local magnetization of Co andMn impurities in the reentrant spin glass Au0.82Fe0.18

The low-temperature nuclear orientation technique has been used to study the magnetic behaviour of⁶⁰Co and⁵⁴Mn impurity atoms in the reentrant spin glass Au_0.82Fe_0.18. The results obtained for⁶⁰Co indicate that Co moments follow the distribution of Fe directions. In contrast, Mn moments show a spread directional distribution. These results are the consequence of the different character of Mn-Fe andFe-Fe interactions at short distances.     

Mössbauer and PAC studies of nanocrystalline Fe

High-purity Fe powder was mechanically milled under argon at ambient temperature using an SPEX 8000 mill. The local atomic and magnetic structure was studied using⁵⁷Co/Fe Mössbauer and¹¹¹In/Cd perturbed angular correlations (PAC) spectroscopies. After 32 hours of milling, X-ray diffraction revealed effective grain diameters of 18 nm and energy-dispersive X-ray analysis indicated a Cr impurity concentration of 5%, presumably introduced by mechanical attrition of steel ball bearings used for milling. In addition to a spectral component very similar to bulk iron metal, the Mössbauer spectra exhibited hyperfine field shifts attributed to the Cr impurities. PAC spectra on Fe milled for 5 h, with no contamination, exhibited two components: (1) A slightly broadened magnetic interaction attributed to interior, defect-free sites of In/Cd probes with a mean hyperfine field slightly greater than in macroscopic grains. The defect-free site fraction grew appreciably during milling, even though In is essentially insoluble in Fe. (2) An indistinct signal due to mixed magnetic and quadrupole interactions attributed to probes at surface or other defect sites.     

Experimental evidences of clusters with different short range order in amorphous alloys

⁵⁶Fe,⁵⁷Fe,¹⁰B and¹¹B isotopes were used for binary alloys. The signals of B (40,5 MHz) and Fe (43 MHz) from α-Fe in binary Fe−B crystalline and amorphous alloys were found besides the signals of these nuclei in t-and o-phase or clusters like these phases. The NMR on (51)V impurity nuclei in Fe−B alloys was used as well. Only amorphous Fe-(^<15 at.%B) alloys had the clusters with o-, t-Fe₃B and α-Fe short range order.     

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.     

Impurity-concentration dependence of internal magnetic field acting on platinum in ferromagnetic iron metal

It was found by perturbed angular correlation that the internal magnetic fields acting on platinum in iron were kept in a definite value for uniform alloy samples with impurity concentration ranging from 2 at% to 0.1 at%. Theg-factor of 355.7 keV level of¹⁹⁶Pt was revised tog=0.335±0.018 using the refined ωτ.     

Magnetoplastic effect in silicon: A search for new methods of controlling structure-sensitive properties of elemental semiconductors

The effect of static magnetic fields up to 1 T on the state of impurity point defects and the mobility of surface dislocation segments in doped (0.01–1.00 Ω cm) silicon has been considered. Long-lived (∼100 h) changes in the state of point defects have been revealed from the mobility of dislocations introduced after the magnetic-field treatment. The concentration dependence of the magnetoplastic effect in p-type silicon has been studied. A threshold impurity concentration of 10¹⁵ cm⁻³ has been found, below which the magneto-plastic effect has not been observed. The influence of magnetic-field pretreatment on the expectation times and activation barriers for dislocation depinning from stoppers and the effect of thermal preannealing on the magnetoplasticity in Si have been considered.     

Studies of weak electric quadrupole interaction in57,60CoFe using modulated adiabatic passage on oriented nuclei

The electric quadrupole interactions at⁵⁷Co and⁶⁰Co in co-diffused^57,60CoFe single crystal have been measured using Modulated Adiabatic Passage on Oriented Nuclei (MAPON). The quadrupole splittings Δν_Q<100> are + 18(2) kHz for⁵⁷Co and +9(2) kHz for⁶⁰Co, corresponding to a principal electric field gradient (efg) tensorV _zz =2.0(5)×10¹⁹ Vm⁻² and 2.5(6)×10¹⁹ Vm⁻², respectively, in broad agreement with previous MAPON results for CoFe. The distributions of the efg’s are very similar for the two isotopes, verifying that previously reported differences in⁵⁸CoFe and⁶⁰CoFe could be attributed to different host preparations. The measurement of such weak efg’s which are not spectroscopically resolved, allows determination of new nuclear electric quadrupole moments, not accessible by other techniques. Applications to other systems are discussed.     

Effect of Fe substitution on the phase stability and magnetic properties of Mn-rich Ni-Mn-Ga ferromagnetic shape memory alloys

The influence of Fe additions on the martensitic transformation and magnetic properties of Mn-rich Ni-Mn-Ga alloys was investigated by substituting either 1 at% Fe for each atomic species or by substituting Ni with varying amounts of Fe. The magnetic structure of the alloys was studied using ⁵⁷Fe Mössbauer spectroscopy. Mössbauer spectra revealed typical paramagnetic features in Mn-rich Ni-Mn-Ga-Fe alloys owing to the preferential site occupancy of Fe atoms at Ni sites. The evolution of the magnetic properties and phase stability has been correlated with the chemical and atomic ordering in these alloys.     

Variation in the fluorescent background in Raman spectra of distilled water purified by different methods

The contribution of impurity fluorescence was determined in the water Raman spectra excited by the second harmonic (λ = 532 nm) of a pulsed Nd:YAG laser. Water samples prepared by different techniques (tap water (undistilled), distilled water, Milli-Q water, water for injections, and water subjected to cavitation treatment) were investigated. The Raman (bands at ν ₂ ∼ 1550 cm⁻¹ and ν ₃ ∼ 3400 cm⁻¹) and fluorescence (Stokes shift 2500 cm⁻¹) signals were separated spectrally and according to the differences in the emission kinetics. It was established that all investigated samples, including distilled and specially purified water for injections, exhibit afterglow. The highest sensitivity to the presence of impurities was revealed near ∼ 2500 cm⁻¹. The least contribution to the fluorescence signal was found in the water for injections.