Hyperfine Magnetic Field Distribution Research Articles

Structural and hyperfine evolution of the (Fe 79Mn 21) 1− xCu x system under milling time

The evolution with milling time ( t m) of the structural and hyperfine properties of mechanically alloyed (Fe 79Mn 21) 0.85Cu 0.15 and (Fe 79Mn 21) 0.70Cu 0.30 nominal composition samples are reported. The samples milled during t m = 1, 3, 6, 9, 12, 15 and 18 h are characterized by X-ray diffraction (XRD) and Mössbauer spectroscopy. From the XRD results two phases are observed, a BCC one corresponding to α-Fe(Mn, Cu) and a FCC-phase associated to Fe–Mn–Cu solid solution. Mössbauer spectra show complex structure evidencing several Fe environments. Two hyperfine magnetic field distributions were used to reproduce the spectra, a high magnetic field interaction ascribed to the BCC phase and a low hyperfine magnetic field distribution linked to the FCC solid solution. An increment in the average hyperfine magnetic field ( B hf) and in the isomer shift ( δ) values of the low hyperfine magnetic field distribution is observed when the milling time increases. All the structural and hyperfine parameters remain without changes after 9 h of milling. Once this stationary regime is archived, the B hf of the (Fe 79Mn 21) 0.85Cu 0.15 sample resulted higher than that of the (Fe 79Mn 21) 0.70Cu 0.30 one.

Effect of Ni on the lattice parameter and the magnetic hyperfine field in (Fe70Al30)100 − x Ni x alloys

Samples of the (Fe70Al30)100 − x Ni x system, with x = 5, 10, 15, and 20, were prepared by mechanical alloying using milling times of 12, 24, 36, 48, and 72 h and characterized by X-ray diffraction (XRD) and Mossbauer spectrometry (MS). XRD of all the samples allowed us to identify the BCC structure as the main component. A decreasing lattice parameter, as the milling time and Ni content increase, was obtained. The MS experiments were carried out at room temperature. The spectra were fitted with a hyperfine magnetic field distribution (HMFD). The Mean Hyperfine Fields (MHF) are ranged between 27 and 29 T with a small dependence with the milling time and was not strongly influenced by Ni content. An additional paramagnetic single line in the spectra of samples with x = 20 and that of sample with x = 15 and milled during 72 h must be included. The Mossbauer spectral area of this phase increases when the milling time increases and it was associated to an FCC phase.

Structural and magnetic properties of Fe–Ni mecanosynthesized alloys

Fe100 − xNix samples with x = 22.5, 30.0 and 40.0 at.% Ni were prepared by mechanical alloying (MA) with milling times of 10, 24, 48 and 72 h, a ball mass to powder mass (BM/PM) ratio of 20:1 and rotation velocity of 280 rev/min. Then the samples were sintered at 1,000°C and characterized by X-ray diffraction (XRD) and transmission Mossbauer spectrometry (TMS). From the refinement of the X ray patterns we found in this composition range two crystalline phases, one body centered cubic (BCC), one face centered cubic (FCC) and some samples show FeO and Fe3O4 phases. The obtained grain size of the samples shows their nanostructured character. Mossbauer spectra were fitted using a model with two hyperfine magnetic field distributions (HMFDs), and a narrow singlet. One hyperfine field distribution corresponds to the ferromagnetic BCC grains, the other to the ferromagnetic FCC grains (Taenite), and the narrow singlet to the paramagnetic FCC grains (antitaenite). Some samples shows a paramagnetic doublet which corresponds to FeO and two sextets corresponding to the ferrimagnetic Fe3O4 phase. In this fit model we used a texture correction in order to take into account the interaction between the particles with flake shape and the Mossbauer \(\upgamma\)-rays.

119Sn Mössbauer spectroscopy of the intermetallic compound HoRhSn

The powder X-ray diffraction data revealed that the structure of HoRhSn is isotypic with the hexagonal ZrNiAl type (space group P 6 ¯ 2 m ). Bulk magnetic AC and DC measurements have shown that this compound is ferromagnetic with a Curie temperature of T C = 6.3(2) K. The thermal variation of the hyperfine parameters has been studied in detail by 119Sn Mössbauer spectroscopy. Especially, large distribution of magnetic hyperfine fields observed at the tin sites points to a rather complicated magnetic structure of probably non-collinear character but with the magnetic holmium moments arranged in directions close to the c-axis.

Detailed Mössbauer study of the cation distribution in CoFe2O4 ferrites

Partially inverted (Co0.185Fe0.815)[Co0.815Fe1.185]O4 spinel submicron particles with spherical shape are studied at low temperature by Mossbauer spectroscopy. Canted magnetic structures are evidenced. The hyperfine magnetic field distributions P(H hf ) have been simulated by model with two polynomial cation distributions for A- and B-sites. The influence of the second nearest-neighbours and perturbation effect of the third nearest-neighbours are taken into account. The synthesized magnetic field distributions cannot fit with high precision the experimentally observed one. Better explanation is possible if clustering, predominantly occupation of some crystallographic planes with Co2 + ions, formation of cobalt super lattice and submicron surface layer with spin pinning effects are taken into account.

Structural and thermal changes induced by mechanical alloying in a Fe–Ni based amorphous melt-spun alloy

In this work, a Fe–Ni rich (80 at%) melt-spun amorphous alloy is obtained and mechanically alloyed under two milling conditions to obtain a powdered alloy. The morphology, structure and thermal behavior were analyzed as a function of milling time and conditions. The milling process is able to separate the amorphous phase in two Fe–Ni phases, one Fe–Ni richer than the other. From Mössbauer analysis, the Fe–Ni rich zone corresponds to a ferromagnetic phase with a hyperfine magnetic field distribution similar to an amorphous structure but with a higher (about 22%) average magnetic field. The increase on the magnetic field during the milling process provokes the shift of the main peak to higher fields, but the secondary peak remains in the same position and, in consequence, the distribution of magnetic fields becomes broader. A paramagnetic phase was found near 2 T. The thermal stability was followed by differential scanning calorimetry. Activation energies of the main crystallization transition were determined using the Kissinger analysis for the as quenched and the powdered-like materials. Slight diminution (about 10%) was found after mechanical alloying. Nevertheless, the crystallization processes has higher thermal stability than alloys directly developed by mechanical alloying.

Structure and hyperfine interactions of mechanically synthesized Co–Fe–Ni alloys

Mechanical alloying method was applied to prepare Co 50Fe 40Ni 10, Co 40Fe 40Ni 20, Co 50Fe 35Ni 15 and Co 60Fe 30Ni 10 alloys. X-ray diffraction and Mössbauer spectroscopy were used as complementary methods to obtain structural and hyperfine interactions data of the as-milled samples. X-ray diffraction proved that during mechanical alloying process the solid solutions with b.c.c. lattice were obtained in the case of Co 50Fe 40Ni 10, Co 50Fe 35Ni 15 and Co 60Fe 30Ni 10 alloys, while for Co 40Fe 40Ni 20 composition the solid solution with f.c.c. lattice was formed. Result obtained for Co 50Fe 40Ni 10 alloy is consistent with the phase diagram for the Co–Fe–Ni bulk alloys prepared by melting. On the other hand, the milling process of Co 40Fe 40Ni 20, Co 50Fe 35Ni 15 and Co 60Fe 30Ni 10 alloys resulted in the formation of the single solid solution, while for these chemical concentrations the melted alloys are a mixture of b.c.c + f.c.c. phases. Mössbauer spectroscopy revealed hyperfine magnetic field distributions, which reflected the different surroundings of 57Fe isotopes by Co, Fe and Ni atoms, depending on the chemical composition of the alloy. The most probable atomic configurations were determined on the basis of the local environment model.

Mössbauer and x-ray study of mechanically alloyed Fe–Ni alloys around the Invarcomposition

Fe100−xNix powders(22.5≤x≤40 at.%)mechanically alloyed (MA) for 10 h were characterized by x-ray diffraction (XRD) and transmission57Fe Mössbauer spectrometry (TMS). In all of this composition range, the nanostructured alloysconsist of two crystalline phases, body-centred cubic (BCC) and face-centred cubic (FCC).The Mössbauer spectra were fitted by means of a new fitting model involving two hyperfinemagnetic field distributions (HMFDs), and a narrow singlet. One HMFD corresponds tothe ferromagnetic BCC grains (tetrataenite), and the other to the ferromagnetic FCCgrains (taenite), and the narrow singlet to paramagnetic FCC grains (antitaenite orsuperparamagnetic FCC grains). The Ni content dependence of the hyperfine field at57Fe nuclei of the FCC phase gives evidence for some jump at about 32.5 at.% Ni, attributed toInvar anomaly.

Magnetic properties of the magnetoelectricAl2−xFexO3 (x = 0.8,0.9 and 1)

By using x-ray diffraction, magnetization and Mössbauer spectroscopy techniques we have studied themagnetoelectric Al2−xFexO3 (x = 0.8,0.9 and1.0) compound. Ac-susceptibility and magnetization measurements revealed magnetic transitions atTN = 180,210 and260 K for x = 0.8, 0.9 and 1.0 respectively, that can be attributed to the Néel temperatures of ferrimagneticto paramagnetic phase transition for all samples. Mössbauer spectra for the three sampleswere recorded between 4.2 and 295 K. Above the Néel temperature the paramagnetic spectracan be analyzed by three quadrupole doublets associated with the octahedral Fe1, Fe2 andFe4 sites. The values of the hyperfine parameters show that iron ions are in the high spinFe3+ state. The spectrum area of the doublet with larger quadrupole splitting increases withx, andin combination with x-ray diffraction results it can be attributed to the iron which occupies the Fe4 site.Below TN(x) the Mössbauer spectra are magnetically split and atT = 4.2 K consist of six broad lines, indicating either a hyperfine magnetic field distribution(P(Hhyp)) or that the three octahedral sites give three unresolved sextets. The most probable value ofHhyp (the maximumvalue of P(Hhyp)) follows a power law indicative of a second order transition, in agreementwith ac-susceptibility and magnetization measurements. The width ofP(Hhyp) increases drastically toward low hyperfine magnetic fields as temperature increases. In addition,an appreciable percentage of the iron nuclei sense a hyperfine field with values in the interval[0,Hmax]. This behavior can be explained by assuming that several magnetic sites with differentsuperexchange parameters exist.

Mössbauer study of nanocrystalline Co60Fe30Ni10 and Co50Fe35Ni15 alloys obtained during mechanical synthesis

The mechanical alloying method was used to prepare Co60Fe30Ni10 and Co50Fe35Ni15 alloys from the elemental powders. As X-ray diffraction studies proved the final products of milling were the solid solutions with b.c.c. lattice and the average grain size of about 60 nm. After heating of the alloys up to 993K, the mixtures of two solid solutions with a b.c.c. and f.c.c. lattices were formed. Annealing of the alloys at 1173 K for 1 h resulted in the formation of solid solutions with an f.c.c. lattice. Mössbauer spectroscopy revealed hyperfine magnetic field distributions which reflected the different surroundings of 57Fe isotopes by Co, Fe and Ni atoms, depending on the chemical composition of the alloy. The most probable atomic configurations were determined on the basis of a local environment model. The results of the macroscopic magnetic measurements testified that Co60Fe30Ni10 and Co50Fe35Ni15 alloys exhibited relatively good soft magnetic properties.

Magnetic properties of HoFe2Hx

The magnetic hyperfine field distribution that is associated with the number of hydrogen nearest neighbors of iron atoms in HoFe2Hx has been determined. From an analysis of the isomer shift values the 4s electron transfer from iron to hydrogen and the intra-atomic 3d-4s electron transfer has been calculated.

Mössbauer study of ferromagnetic metallic glasses irradiated by swift heavy ions at temperatures 100 and 300 K

The effect of swift heavy ion irradiation on ferromagnetic metallic glasses Fe40Ni38Mo4B18 and Fe78Si9B13 has been studied. The ion beams used are 100 MeV 127I and 180 MeV 197Au. The specimens were irradiated at fluences ranging from 3 × 1012 to 1.5 × 1014 ions/cm2. The irradiations have been carried out at temperatures 100 and 300 K. The magnetic moments are sensitive towards the irradiation conditions such as irradiation temperature and stopping power of incident ion beam. The irradiation-induced effects have been monitored, by using Mossbauer spectroscopy. The modifications in magnetic anisotropy and hyperfine magnetic field distributions, as an effect of different irradiation temperature as well as different stopping power have been discussed. After irradiation, all the samples remain amorphous and magnetic anisotropy considerably changes from its original in-plane direction. The results show enhancement in magnetic anisotropy in the specimen irradiated at 100 K, as compared to that of irradiated at 300 K. It is expected that at low temperature, the stresses produced in the material would remain un-annealed, compared to the samples irradiated at room temperature and therefore, the modification in magnetic anisotropy would be enhanced. A distribution of hyperfine magnetic field, of the samples irradiated at low temperature, show a small but distinct peak at ∼ 11 Tesla, indicating Fe-B pairing.

Effect of vanadium neighbors on the hyperfine properties of iron–vanadium alloys

The electronic and magnetic structures of Fe–V alloys are calculated using the discrete-variational and full-potential linearized-augmented-plane wave methods. The derived hyperfine properties at Fe sites are studied against the number of Fe atoms in the neighbouring shells. As expected the magnetic hyperfine field depends strongly on the number of Fe atoms in the first and second shells of neighbours while its dependence on the variation of atoms in the third shell is weak. The calculated distribution of the magnetic hyperfine fields at the Fe sites, are compared to the experimental data of Krause et al. (Phys Rev B 61:6196–6204, 2000). The contact charge densities and the magnetic moments are also calculated. It was found that the contact charge density increases with increasing V contents and this leads to negative isomer shift on addition of V.

The Effect of Mn and B on the Magnetic and Structural Properties of Nanostructured Fe60Al40 Alloys Produced by Mechanical Alloying

The effect of Mn and B on the magnetic and structural properties of nanostructured samples of the Fe60Al40 system, prepared by mechanical alloying, was studied by 57Fe Mössbauer spectrometry, X-ray diffraction and magnetic measurements. In the case of the Fe(60-x)Mn(x)Al40 system, 24 h milling time is required to achieve the BCC ternary phase. Different magnetic structures are observed according to the temperature and the Mn content for alloys milled during 48 h: ferromagnetic, antiferromagnetic, spin-glass, reentrant spin-glass and superparamagnetic behavior. They result from the bond randomness behaviour induced by the atomic disorder introduced by the MA process and from the competitive interactions of the Fe-Fe ferromagnetic interactions and the Mn-Mn and Fe-Mn antiferromagnetic interactions and finally the presence of Al atoms acting as dilutors. When B is added in the Fe60Al40 alloy and milled for 12 and 24 hours, two crystalline phases were found: a prevailing FeAl BCC phase and a Fe2B phase type. In addition, one observes an additional contribution attributed to grain boundaries which increases when both milling time and boron composition increase. Finally Mn and B were added to samples of the Fe60Al40 system prepared by mechanical alloying during 12 and 24 hours. Mn content was fixed to 10 at.% and B content varied between 0 and 20 at.%, substituting Al. X-ray patterns show two crystalline phases, the ternary FeMnAl BCC phase, and a (Fe,Mn)2B phase type. The relative proportion of the last phase increases when the B content increases, in addition to changes of the grain size and the lattice parameter. Such behavior was observed for both milling periods. On the other hand, the magnetic hyperfine field distributions show that both phases exhibit chemical disorder, and that the contribution attributed to the grain boundaries is less important when the B content increases. Coercive field values of about 10(2) Oe slightly increase with boron content. Comparison with previous results on FeAIB alloys shows that Mn promotes the structural stability of the nanostructured powders.

Iron oxide colloids and their heterogenization by silica sol–gel entrapment: Catalytic and magnetic properties

Abstract Fe3O4 colloids modified by the chiral ligand cinchonidine were prepared with the goal of obtaining a magnetic and catalytic nano-material and were subsequently embedded in silica to form a heterogeneous catalyst. The systems were characterized by TEM and XRD measurements, while the Mossbauer technique was applied for measuring the magnetic properties of the Fe3O4 colloids. The hyperfine magnetic field distribution was consistent with one type of Fe oxide, namely, the magnetite (Fe3O4). These colloids, both as ‘quasi-homogenous catalysts’ (or soluble heterogeneous catalysts) and embedded in silica (heterogeneous catalysts) were employed in the selective hydrogenolysis of complex bicyclo[2.2.2]oct-7-enes (bicyclo[2.2.2]oct-2-enes when unsubstituted).

Influence of Cobalt Substitution on Hyperfine Interactions in (Fe1-xCox)76Mo8Cu1B15Alloys

The effect of cobalt substitution on structure, magnetic behaviour, magnetic arrangement, and hyperfine interactions in (Fe1−xCox)76Mo8Cu1B15 (x = 0, 0.1, 0.2, 0.25, 0.5) is studied by the Mossbauer spectrometry for both as-quenched and annealed alloys. Partial substitution of Fe by Co resulted in an enhancement of the average value of hyperfine magnetic field distributions as a function of x probably due to higher magnetic moment of Co. After annealing, a two-phase nanocrystalline structure composed of amorphous matrix and bcc-FeCo nanocrystallites was observed. Mossbauer spectra were fitted with up to four six-line patterns of narrow lines assigned to different number of Co nearest neighbours inside a bcc-FeCo lattice.

Modeling of Magnetic Hyperfine Field Distribution for Spherical Nanoparticles of bcc Structure

Modeling of Magnetic Hyperfine Field Distribution for Spherical Nanoparticles of bcc Structure

Influence of aging in an alkaline medium on the microstructural properties of α-FeOOH

The influence of the aging in a highly alkaline medium at 160 °C on the microstructural properties of α-FeOOH was monitored by XRD, 57Fe Mössbauer and FT-IR spectroscopies and FE-SEM. In the synthesis of acicular and monodisperse α-FeOOH particles, tetramethylammonium hydroxide was used as a precipitating agent. The crystal growth of α-FeOOH by the mechanism of lateral arraying was observed with prolonged aging time. Smaller α-FeOOH particles were dissolving with time, thus providing Fe ( OH ) 4 - ions for the additional growth of α-FeOOH particles and improvement of their crystal shape. The XRD analysis confirmed that the growth of α-FeOOH crystallites perpendicularly to the crystallographic c-axis was favoured. The Mössbauer spectrum of α-FeOOH showed a distribution of the hyperfine magnetic field (HMF) which gradually narrowed with a longer aging time. The average value of the HMF distribution was shifted from 35.3 to 37.1 T between 2 and 168 h of aging. Characteristic IR bands of α-FeOOH were sensitive to the microstructural changes of α-FeOOH particles during their aging in the suspension in a highly alkaline medium at 160 °C.

A novel shape transformation of Fe–MgO nanocomposites: microstructural, magnetic and hyperfine investigations

Fe–MgO nanocomposites synthesized by the mechanical high-energy transfer technique were characterized by x-ray diffraction (XRD), transmission electron microscopy, Mössbauer spectroscopy and dc magnetization studies. By varying the duration of milling, powder with different grain sizes in the range 17–40 nm was produced. XRD and Mössbauer measurements could not detect the presence of any form of iron oxide in the nanocomposites. Transmission electron micrographs showed a shape transformation from spherical to acicular-like geometry in the samples ball milled for more than 36 h. Dc magnetization measurements show an increase in the coercive field with decrease in average grain size, with a sharp increase at the point of shape transformation. A marked decrease from the expected values of saturation magnetization and magnetic moment per formula unit was observed. This decrease was ascribed to the magnetic dead layer formed at the surface of the nanoparticles, which increased with the increase in milling time. The nanocomposites ball milled for more than 36 h exhibit a two-component Mössbauer spectra due to the presence of two phases: a crystalline phase and an additional phase corresponding to the atoms residing at the grain boundaries between the crystallites. The grain boundaries give rise to a distribution of hyperfine magnetic fields, typical of an amorphous-like compound.

Structure and some magnetic properties of mechanically synthesized and thermally treated Co–Fe–Ni alloys

Mechanical alloying method was applied to prepare nanocrystalline Co 40Fe 40Ni 20, Co 50Fe 40Ni 10, Co 52Fe 26Ni 22 and Co 65Fe 23Ni 12 alloys. X-ray diffraction, Mössbauer spectroscopy and magnetization measurements were used as complementary methods to obtain structural data and to determine magnetic properties of the as-milled as well as the thermally treated samples. X-ray diffraction proved that during mechanical alloying process the Co–Fe–based solid solution with BCC lattice was formed in the case of Co 40Fe 40Ni 20 and Co 50Fe 40Ni 10, while for Co 52Fe 26Ni 22 and Co 65Fe 23Ni 12 systems the Co–Ni–based solid solutions with FCC lattice were obtained. Mössbauer spectroscopy revealed hyperfine magnetic field distributions, which reflect the different surroundings of 57Fe isotopes by Co, Fe and Ni atoms, depending on the chemical composition of the alloy. The most probable atomic configurations were determined on the basis of the local environment model. Thermal treatment of the mechanosynthesized alloys led in some cases to decomposition of the suitable solid solution into the mixture of two solid solutions. In other cases, the phase composition of the alloys was stable or the type of the crystalline lattice was changed during annealing. Moreover, thermal treatment led to an increase in the grain size and a decrease in the level of internal strains that influenced the magnitudes of the effective magnetic moments and Curie temperatures of the investigated alloys.