Hyperfine Magnetic Field Values Research Articles

Vickers Microhardness and Hyperfine Magnetic Field Variations of Heat Treated Amorphous Fe78Si9B13 Alloy Ribbons

Amorphous Fe78Si9B13 alloy ribbons were heat treated between 296 and 763 K, using heating rates between 1 and 4.5 K/min. Whereas one ribbon partially crystallized at T x = 722 K, the other one partially crystallized at T x = 763 K. The partially crystallized ribbon at 722 K, heat treated using a triangular form for the heating and cooling rates, was substantially less fragile than the partially crystallized at 763 K where a tooth saw form for the heating and cooling rates was used. Vickers microhardness and hyperfine magnetic field values behaved almost concomitantly between 296 and 673 K. The Mossbauer spectral line widths of the heat-treated ribbons decreased continuously from 296 to 500 K, suggesting stress relief in this temperature range where the Vickers microhardness did not increase. At 523 K the line width decreased further but the microhardness increased substantially. After 523 K the line width behave in an oscillating form as well as the microhardness, indicating other structural changes in addition to the stress relief. Finally, positron lifetime data showed that both inner part and surface of Fe78Si9B13 alloy ribbons were affected distinctly. Variations on the surface may be the cause of some of the high Vickers microhardness values measured in the amorphous state.

Magnetism of amorphous Fe 2 O 3 nanopowders synthesized by solid‐state reactions

Monodispersed amorphous Fe2O3 nanoparticles with the size ranging from 1 to 4 nm have been prepared by thermally induced oxidative decomposition of Prussian Blue, Fe4[Fe(CN)6]3, in air. Amorphous nanopowders exhibit specific magnetic behaviour strongly affected by interparticle interactions and extremely low particle size with a high contribution of the surface anisotropy as illustrated by temperature dependent and external field Mossbauer spectroscopy and magnetization measurements (4–300 K). Some of the properties are in close similarity to those of spin glasses including the fast thermal variation of superparamagnetic fraction in the Mossbauer spectra, or the particle size independence of the blocking temperature, and non-saturation of magnetization even at 5 K and magnetic field of 10 T. The reduced value of internal magnetic hyperfine field (∼49 T at 5 K) and no indications of the tetrahedral Fe3+ sites in the 5T/5K external field Mossbauer spectra are the principal found differences in comparison with the magnetic behaviour of nanocrystalline γ-Fe2O3. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Crystal structure and magnetic properties of the UFe 7Al 5 uranium–iron aluminide

The ternary compound UFe 7Al 5 was synthesized by arc melting, followed by annealing at 850°C. The crystal structure was determined by single-crystal X-ray diffraction and refined to a residual value of R=0.039 ( S=1.030), with lattice parameters a=8.581(2) Å and c=4.946(1) Å. This compound is a new extreme composition in the family of intermetallics with general formula UFe x Al 12− x crystallizing in the tetragonal ThMn 12-type structure, space group I4 /mmm. In contrast to UFe x Al 12− x within the composition range 4⩽ x⩽6, in UFe 7Al 5 the additional iron atom is found in the 8 i equipositions. Magnetization measurements versus temperature show two magnetic transitions at 363 and 275 K, respectively, with a ferromagnetic behavior below the highest temperature transition. 57Fe Mössbauer data indicate that the high-temperature transition is related to the ordering of the iron atoms. The dependence of the isomer shifts and magnetic hyperfine fields on the crystallographic site and on the number of the iron nearest neighbors is similar to that observed in the other UFe x Al 12− x and rare-earth analogues. The magnetic hyperfine field values of iron atoms on 8 i sites is larger than in the other sites, in agreement with previous data obtained for other ThMn 12-type compounds.

Hyperfine interactions in the iron cores from various pharmaceutically important iron–dextran complexes and human ferritin: a comparative study by Mössbauer spectroscopy

Mössbauer spectroscopy has been used to study the hyperfine interactions in the iron cores of pharmaceutically important industrial and elaborated iron–dextran complexes (ferritin models) and human ferritin. Mössbauer spectra of frozen solutions and lyophilized samples of iron–dextran complexes at 87 K demonstrated magnetic, superparamagnetic and paramagnetic states of iron in various complexes. Mössbauer spectra of human ferritin in frozen solution and lyophilized form showed paramagnetic state of iron at 87 K. Small variations of Mössbauer hyperfine parameters were observed for different samples at 87 and 295 K, respectively, supposing the homogenous iron cores. The values of quadrupole splitting for iron–dextran complexes and ferritin in frozen solutions at 87 K varied from 0.639 to 0.744 mm/s while those of lyophilized samples at 87 K varied from 0.714 to 0.788 mm/s. The values of quadrupole splitting for iron–dextran complexes and ferritin in lyophilized form at 295 K varied from 0.687 to 0.741 mm/s. The values of hyperfine magnetic fields on the 57Fe nuclei in several iron–dextran complexes at 87 K varied from ∼231 to ∼485 kOe. These small variations of the hyperfine parameters were related to several types of the hydrous iron oxide microstructural modifications in the core and variations of the iron core size. The influence of lyophilization on the iron core structure was also assumed. In addition, Mössbauer spectra were evaluated in supposition of heterogeneous iron core in all samples.

Mössbauer and X-ray Diffraction Studies of Zr1-xTixFe2Laves Phase Compounds

Mossbauer spectroscopy of 5 7 Fe and X-ray diffraction measurements in the Zr 1 - x Ti x Fe 2 phase have been made. Our X-ray diffraction spectra revealed that the samples have the cubic C15 crystal structure for low Ti concentration and the hexagonal C14 structure for high Ti concentration. In the range of 0.2 0.80 and magnetic for x ≤ 0.8. In the magnetic samples we found four different values of hyperfine magnetic fields. The presence of two hyperfine magnetic fields in the C14 phase suggests magnetic moments on Fe atoms at 2a sites. The obtained e Q vs. the x dependence indicates the spin canted antiferromagnetic structure in the hexagonal phase in the range of 0.2 < x < 0.8.

MAGNETIC PROPERTIES OF NANOCRYSTALLINE NiFe2O4 POWDERS PREPARED BY AN AQUEOUS OXIDATIVE PRECIPITATION PROCESS

Nanocrystalline NiFe 2 O 4 powder has been prepared by an oxidative precipitation process at room-temperature and the crystallite size dependent magnetic properties have been studied. The NiFe 2 O 4 powders prepared at room-temperature had an average crystallite size of 6 nm and showed a reduced saturation magnetisation (M s ) of 3 emu · g -1. The crystallite size was increased by heating the samples to increasingly higher temperatures. The M s value increased from 3 to 40 emu·g -1 as the crystallite size was increased from 6 to 120 nm. The samples having crystallite sizes from 6 to 20 nm were superparamagnetic at room-temperature. The Mössbauer spectrum of the 6 nm sized sample showed a broad quadruple doublet, whereas, the 40 nm sized sample showed a clear sextet pattern, with a hyperfine field values of 466 and 504 kOe for A(tetraheral) and B(octahedral) sublattices, respectively. It is shown that the saturation magnetisation and magnetic hyperfine field values are significantly reduced in nanocrystalline NiFe 2 O 4 as a function of crystallite size.

Symmetry and hyperfine magnetic fields in Nd-based intermetallics

Intermetallics of the type NdCo 9− x Fe x Si 2C y ( x=3; 5; 6; 7 and y=0; 1) and Nd 2Co 15− x Fe x Si 2C y ( x=7; 9; 12 and y=0; 1) were prepared by arc melting in order to study the competing effects of Fe and Co substitutions on the magnetic hyperfine fields as well as the effects of interstitial carbon additions on the symmetry and local magnetic properties in these systems. The investigations were performed by X-ray diffraction, Mössbauer spectroscopy and hysteresis loop measurements. Both site and average hyperfine magnetic field values were analyzed in order to discriminate between the Fe and Co contributions to the local atomic environments in these systems. While a higher Fe content as well as a higher Co content can both lead to an increase in the site magnetic fields, it was found that the model based on hyperfine field distributions provides a better description of the trends observed in hyperfine magnetic fields in these compounds.

Distributions of the hyperfine interaction parameters in (Er 1− xSm x) 2Fe 14B as seen by Mössbauer spectroscopy

The distributions of the hyperfine interaction parameters, caused by substitution of Sm for Er in the (Er 1− x Sm x ) 2Fe 14B system, were studied by Mössbauer spectroscopy both at room and liquid nitrogen temperatures. It was proved that the random distribution of the rare earth atoms over their crystal sites and the additive contribution of the Sm atoms to the values of the hyperfine interaction parameters at the iron crystal sites lead to a linear dependence of the average values of the 57Fe hyperfine magnetic field, isomer shift and quadrupole interaction on the Sm concentration in the present compounds. From these linear relations, the contributions Δ H , Δ IS and Δ QS to the values of the hyperfine magnetic field, isomer shift and quadrupole interaction, caused by the presence of the Sm atom in the nearest neighbour shell of the Fe crystal sites, were derived. No distinct correlations were found between the Δ H , Δ IS and Δ QS values and those of the nearest neighbours and/or their distances from the Fe crystal sites.

Structure and Mössbauer studies of Cu-doped Ni–Zn ferrite

Ni 0.65Zn 0.35Cu x Fe 2− x O 4 ( x=0.0–0.3) was studied with X-ray diffraction, Mössbauer spectroscopy and vibrating sample magnetometer (VSM). The crystal structure was found to be a cubic spinel, and the lattice constants increased linearly with increasing quantity of Cu ions with the lattice constant a 0 =8.384±0.005 A ̊ at x=0.0. Mössbauer spectra of Ni 0.65Zn 0.35Cu x Fe 2− x O 4 ( x=0.0–0.3) were taken at various temperatures ranging from 12 to 725 K. As the temperature increased toward T N , a systematic line broadening effect in the Mössbauer spectra was observed and was interpreted as originating from different temperature dependencies of the magnetic hyperfine fields at various iron sites. The isomer shifts indicated that the iron ions were ferric at the tetrahedral [A] and the octahedral sites [B]. The quadrupole shifts showed that the orientation of the magnetic hyperfine field with respect to the principal axes of the electric field gradient was random. The magnetic hyperfine field values indicated that A sites had more A–O–B superexchange interactions than the B sites. The Néel temperature decreased with increasing quantity of Cu ions with T N =725±2 K at x=0.0. Also, the Debye temperatures of the A and B sites of Ni 0.65Zn 0.35Cu 0.1Fe 1.9O 4 were found to be Θ A =228±5 K and Θ B =328±5 K . The VSM data showed that the magnetic moment decreased with increasing quantity of Cu ions with magnetic moment and coercivity values of M s =66 emu/g and H c=36 Oe at x=0.3.

Structure and Magnetic Properties of Nd-Co-Fe-Si-C Intermetallics

ABSTRACTIntermetallics of the type Nd2Co15−xFexSi2Cy (x=7; 9; 12 and y=0; 1) were prepared by arc melting in order to study the competing effects of Fe and Co substitutions on the magnetic hyperfine fields as well as the effects of interstitial carbon additions on the symmetry and local magnetic properties in these systems. The investigations were performed by x-ray diffraction, Mössbauer spectroscopy and hysteresis loop measurements. Both site and average hyperfine magnetic field values were analyzed in order to discriminate between the Fe and Co contributions to the local atomic environments in these systems. While a higher Fe content as well as a higher Co content can both lead to an increase in the site magnetic fields, it was found that the model based on hyperfine field distributions provides a better description of the trends observed in hyperfine magnetic fields in these compounds.

Magnetic transitions in La1-xYxMn2Si2 - Mössbauer investigation (4.2-520 K)

A set of eight tetragonal La1-xYxMn2Si2 compounds doped with 57Fe and covering the entire range 0 x1 have been investigated by Mössbauer effect spectroscopy over the temperature range 4.2-520 K. Distinct changes in the quadrupole splitting (QS) and magnetic hyperfine field (µ0Hhf) values were observed around critical concentrations of xc~0.15 (4.2 K) and xc~0.2 (room temperature; RT) as the antiferromagnetism of the Y-rich compounds gives way to the predominant ferromagnetism of the La-rich compounds. The temperature dependences of QS and µ0Hhf for the La-rich compounds (x0.25) also show distinct changes in the range ~285-470 K which we relate to the reported magnetic phase transitions occurring in these critical regions. The magnetic phase diagram which we have derived for the La1-xYxMn2Si2 series from our Mössbauer measurements is in excellent agreement with the recent findings of neutron diffraction investigations. We show that analyses of both the Mössbauer and neutron data on LaMn2Si2 give a fully consistent account of the temperature dependent canting of the magnetic structure. Finally, consistent with earlier magnetization measurements, we suggest that a magnetically frustrated state, possibly a spin glass, may exist within the boundary regions of these magnetic phase transitions.

Magnetic properties of amorphous Fe 78P 22 alloy obtained by mechanical grinding

The amorphous Fe 78P 22 alloy obtained by mechanical grinding was studied by X-ray analysis, Mössbauer spectroscopy and magnetic measurements. The measured values of the average hyperfine magnetic field H , mean magnetic moment per Fe atom m Fe and Curie temperature T c agree with those obtained earlier for electrodeposited and then ground samples and are in good qualitative agreement with the model describing macroscopic characteristics through the parameters of local environment but essentially disagree with the literature data for the samples obtained by rapidly quenching and only by electrochemical deposition.

Direct synthesis of nanocomposite of γ-Fe 2O 3 in the copolymer matrix of aniline-formaldehyde in presence of zinc ions

A novel approach for in-situ room temperature synthesis of magnetic nanocomposite of γ-Fe 2O 3 is described. 57Fe Mössbauer spectroscopy has been used to study its magnetic behavior. Observation of a relaxed six line spectrum at room temperature and increase in hyperfine field values at 77 K are typical characteristics of magnetic microcrystalline particles. Interestingly, the studies at high temperature also show an increase in hyperfine magnetic field values, though it is quite unusual for small magnetic particles. This unusual behavior may, however, be attributed to some new kind of interaction between magnetic particles and the polymer matrix, or between magnetic particles themselves caused by conformational changes in the copolymer matrix at higher temperatures. Moreover, these studies clearly indicate that both the polymer matrix and zinc ions play definite roles in the clustering of γ-Fe 2O 3 particles, resulting in the phenomenon of relaxation over a wide range of temperatures.

Neutron irradiation effect on amorphous and nanocrystalline FeZrB(Cu) at low temperature

The microstructure and magnetic properties of the amorphous and nanocrystalline Fe 87.5 −xZr 6.5sB 6Cu x ( x = 0, 1) were studied using Mossbauer spectroscopy at liquid nitrogen temperature. Low temperature measurement of Mossbauer spectra enables a good resolution of the components the sample consist of. Under these conditions effect of neutron irradiation is easily studied through changes of average value of hyperfine magnetic field, hyperfine field distribution and orientation of net magnetic moment. As-cast samples reveal the existence of inequivalent sites of Fe corresponding to broad six line spectra at 77 K. Changes in the orientation of net magnetic moment were observed after neutron irradiation. Considerable changes were observed in the amorphous rest of the nanocrystalline samples. After the neutron irradiation low and high field components are well separated. Field resolution increases towards the higher stage of crystallization. Deviations in a magnetic structure are supposed to be a consequence of changes in a short range order due to neutron irradiation.

Magnetic Hyperfine Fields at Se Adatoms on Ni Surfaces.

Magnetic hyperfine fields for Se on Ni(111) and Ni(001) surfaces were measured with the perturbed angular correlation technique. The results are $|{B}_{\mathrm{hf}}|\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.7(3)$ T for Se on Ni(111) and $|{B}_{\mathrm{hf}}|\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.8(3)$ T for Se on Ni(001) at 90 K. These values of magnetic hyperfine fields of an adatom deviate drastically from the known bulk value of ${B}_{\mathrm{hf}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}15\mathrm{T}$. The surface site positions of the probe atoms are discussed with the aid of the results for the electric hyperfine interactions measured simultaneously.

Physical Properties of Partially Crystallized Fe80B20 Amorphous Alloys

AbstractThe magnetic properties and hyperfine fields were investigated at low temperatures on amorphous Fe80B20 ribbons crystallized at the end of the nucleation-and-growth process without involving coarsening process. The results obtained by SQUID magnetometer and Mössbauer spectrometer show that saturation magnetization and mean magnetic hyperfine field values are greater than those in both the parent amorphous phase and in the fully crystallized structure where coarsening and grain growth processes are involved. Below 200 K irreversibility is observed in low field magnetization measurements. Transmission electron microscopy measurements reveal that spherulites of Fe3B include a radial structure made of small bcc-Fe acicular crystals about 200 nm long and 10 nm wide. In our opinion, magnetic properties and hyperfine fields are ruled by both high magnetic anisotropy of small monodomain acicular bcc-Fe crystallites and the structure of Fe atoms located at their surfaces.

Magnetoresistance and hyperfine fields in Sm xFe 80−xB 20 amorphous alloys

The influence of samarium on the magnetic and electron transport properties of amorphous Sm xFe 80−xB 20, 0 ⩽ × ⩽ 6, was investigated by Mössbauer spectroscopy and by electrical resistivity and magnetoresistance measurements. The resistivity of the alloys increases by about 5% in the temperature range from 78 to 290 K. For Sm 6Fe 74B 20 ribbons a positive contribution to the magnetoresistance was found. The averaged value of the 57Fe hyperfine magnetic field decreases slightly with increasing samarium content. Variations in the line intensities of Mössbauer spectra recorded for ribbons at 78 K indicate a rotation of magnetization towards the normal to the ribbon via positive magnetostriction.

Synthesis of disordered Fe3C alloy by mechanical alloying of iron powder with liquid hydrocarbon (toluene)

Recently a large number of amorphous alloys based on transition metals have been obtained by mechanical alloying [1-5]. Heinike [6] was the first to report the formation of Fe3C by milling iron and carbon powders. Nasu et al. [7] reported about amorphous alloys of Fe3C powders obtained by the mechanical alloying of iron and carbon powders. The aim of this work was to study the possibility of synthesis of amorphous Fe3C alloys by the mechanical treatment of iron powder in liquid hydrocarbon (toluene). The iron powder treatment was performed with a centrifugal planetary mill of Pulverizette type with 25 milling balls (the diameter of the balls, made of tungsten carbide, was 10 ram). 2 g initial powder (the size of the powder particles was ~<300/zm) together with toluene was placed in the closed tungsten carbide container (volume 80 cm 3) of the mill and treated for different times in the range from i to 8 h for each loading. X-ray investigation was carried out with a diffractometer using CoKo~ radiation. The MOssbauer spectra were recorded using a constant-acceleration spectrometer with a 57Co(Cr) source and a resonance scintillation detector. The X-ray and M0ssbauer investigations were carried out at room temperature. Thermomagnetic measurements were performed in the temperature range 77-1100 K with a vibration sample magnetometer and a device for research into magnetic susceptibility. The treatment of powder in toluene leads to essential changes in the MOssbauer spectra and X-ray diffraction patterns in comparison with those of pure 0~-Fe. In the sample spectrum after 4 h grinding the second sextet with a smaller value of hyperfine magnetic field H~ff appears (parameters of H~ff = 20.5 T and isomer shift 6 = 0.1 mms -t in relation to o~-Fe). In the corresponding diffraction pattern of the structural line (110) of the b cc structure of oL-Fe broadening and the appearance of new wide lines of weak intensity at diffraction angles of 20 = 44 and 47 ° were observed. The increase of the treatment time up to 8 h resulted in only a new sextet in the MOssbauer spectrum and a few overlapping broadened lines in the diffraction pattern (Fig. lc). According to the magnetic measurements the specific saturation magnetization at 300 K decreased from 215 A m 2 kg -z for pure oc-Fe to 116 A m e kg -t for powder after 8 h milling. From the analysis of the data obtained, the new state of powders can be concluded to be Fe3C. The formation of Fe3C was confirmed by the diffraction pattern of the powder after 8 h treatment followed by heating for 1 h at 770 K (Fig. ld) [8]. Also, the formation of Fe3C was confirmed by the MOssbauer parameters of the new sextet obtained (as above), which agreed well with the known data for Fe3C [9]. The Curie temperature of this sample was 477 K, which is in accordance with the value known for Fe3C [10]. Thus, after the mechanical treatment of the iron powder in toluene for 8 h, the formation of 100% Fe3C takes place, being confirmed by quantitative analysis of the MOssbauer spectra (Fig. 2). It should be noted that although the lines of the sample spectrum after 8 h milling were broadened,

Characterization of the precipitates formed during the denitration of simulated HRLW

The denitration of several chemical compositions of simulated HRLW (highly radioactive liquid waste) was performed using formic acid as reducing agent. Precipitates formed during the denitration of simulated HRLW were analyzed using X-ray diffraction and57Fe Mossbauer spectroscopy. Goethite and amorphous fraction were the principal phases in these precipitates. It was found that the chemical composition of simulated HRLW and the experimental conditions of denitration have more influence on the crystallinity and the particle size than on the phase composition of the precipitates. Thermal treatment of denitrated precipitates caused the solid state transformation of goethite+amorphous fraction into hematite. The values of hyperfine magnetic field (HMF) of hematite were decreased, thus indicating the substitution of Fe3+ ions with other metal cations.

Mössbauer hyperfine interactions in natural wolframites

Powdered samples of Indian Natural Wolframites, (FexMn1−x) WO4 with x=0.95 to 0.41, obtained from seven different locations of two quartz-wolframite deposits of Degana and Sirohi in Rajasthan, have been investigated by Mossbauer spectroscopy down to 20K and magnetic susceptibility down to 77K. The Mossbauer spectra from 300K to 30K clearly indicate multiple sites which is at variance with the reported work. Below 50K a weak magnetic interaction with Hint∼45Koe is observed. The spectra above transition temperature are resolved in three doublets and explained on the basis of reported crystal structure. The values of isomer shift, quadrupole splitting and magnetic hyperfine field have been attributed to high spin ferrous ions with octahedral symmetry. Relatively small value of Q.S. (∼1.5 mm/sec. at 300K) indicate a strong contribution of the lattice term to the electric field gradient.