Average Hyperfine Magnetic Field Research Articles

Structural ordering and magnetic properties of arc-melted FeGa alloys

X-ray diffraction, Mössbauer spectrometry and magnetic properties have been performed on FeGa arc-melted binary alloys in order to study the compositional dependence of the structural ordering and magnetic properties of these alloys. The average magnetic hyperfine field at 300 K decreases with increasing Ga content as does the average magnetic moment per Fe atom, and a linear dependence between both quantities is found for Ga content up to 20 at%. The substitution of Fe by Ga atoms increases the lattice parameter and causes a change in the order of the crystal structure that has been modelled using a binomial distribution method. The effect of Ga atoms as near neighbours of Fe on the average magnetic hyperfine field is evaluated.

Mössbauer spectrometry of near equiatomic Fe–Cr alloys: Influence of preparation method

Mössbauer spectra reflect the strong sensitivity of the distribution of hyperfine magnetic field distributions (HMFDs) of near equiatomic Fe–Cr alloys to the method of preparation of samples. Whatever the way a bcc Fe 0.51Cr 0.49 alloy is prepared, powders produced from it by ball milling or by filing exhibit a unique HMFD at room temperature. The associated average hyperfine magnetic field, 16 T, is significantly smaller than those of alloys, which are cold-rolled and (/or) annealed at some stage of their preparation process (∼17–19 T).

Structure of the Fe100−x Alx alloys (25 < x < 35 at. %) annealed in a temperature range of 400–800°C and the effect of the ordering type on the magnetic properties

X-ray diffraction was used to determine temperature ranges of annealings that allow the stabilization of the D03 and B2 superstructures in Fe-Al alloys at room temperature upon cooling them at a given rate. A substantial effect of the long-range-order type on the magnetic properties, such as the magnetic-ordering temperature, average magnetic moment per Fe atom, average hyperfine magnetic field at 57Fe nucleus, and coercive force, is demonstrated using the Fe70Al30 alloy as an example.

Mössbauer investigation of Fe 1−x Cr x films grown by ion-beam sputter deposition

Fe 1− x Cr x ( 0 < x < 0.70 ) films, 220 nm thick, on Si and fused-SiO 2 substrates were prepared using ion-beam sputter deposition, and their structural properties were determined by 57Fe conversion electron Mössbauer spectroscopy (CEMS) and X-ray diffraction experiments (XRD) at room temperature. CEM spectra show magnetic ordering for 0< x⩽0.28, and the BCC α-phase is evidenced through XRD diagrams in all cases. The general trend for the films is that the average hyperfine magnetic field (HMF) values are lower compared to bulk counterparts. Moreover, a parabolic change in average HMF with Cr content x could be established. For 0.32⩽ x<0.70, the CEM spectra exhibit a pseudo-single line, which denotes paramagnetic state. Between x = 0.32 and x = 0.38 , there exists a multiphase region where the alloys mainly consist of α and δ (A15-type) phases. Then, in the concentration range x=0.38–0.58, the films only display the metastable δ-phase. For 0.58⩽ x⩽0.66, there appears a new transition region where α- and δ-phases coexist. Finally, the domain of the paramagnetic α-phase alone stretches from x = 0.66 to at least x = 0.70 . Emphasis is placed on the metastable δ-phase which appears over a wide monophase region. Particularly, the site occupancy could be determined through the CEM spectrum for x = 0.49 .

Hyperfine interactions, structure and magnetic properties of nanocrystalline Co–Fe–Ni alloys prepared by mechanical alloying

Mechanical alloying method was used to prepare nanocrystalline Co50Fe40Ni10, Co52Fe26Ni22 and Co65Fe23Nil2 alloys. X-ray diffraction proved that during milling Co-Fe-based solid solution with b.c.c. lattice was formed in the case of Co50Fe40Ni10, while for Co52Fe26Ni22 and Co65Fe23Nil2 compositions Co-Ni-based solid solutions with f.c.c. lattice were obtained. Mossbauer spectroscopy revealed similar values of the average hyperfine magnetic fields for all alloys, e.g. 32.17, 32.24 and 31.21 T for Co50Fe40Ni10, Co52Fe26Ni22 and Co65Fe23Nil2 alloys, respectively. Magnetization measurements allowed to determine the effective magnetic moment, Curie temperature, saturation magnetization and coercive field for the obtained alloys.

Hyperfine interactions and band structures of LaFe 13−xSi x intermetallic compounds with large magnetic entropy changes

Magnetic properties and hyperfine interactions of LaFe 13− x Si x intermetallic compounds with large magnetic entropy changes were investigated by means of Mössbauer spectroscopy, band structure calculation and magnetization measurements. It was found that the 57Fe magnetic hyperfine field at Fe I (8b) site is larger than that at the Fe II (96i) site, whereas the magnetic moment of Fe atoms at the Fe I site is smaller than that of Fe atoms at the Fe II site. The temperature dependence of the average 57Fe magnetic hyperfine field was found to deviate from the mean field model close to T C, implying that the first-order magnetic phase transition is predominant in the sample of LaFe 11.7Si 1.3, and consequently results in a large magnetic entropy change. Furthermore, the effect of Si substitution for Fe on hyperfine parameters was investigated.

Mössbauer effect studies of RFe 11Ti and RFe 11TiH ( R=Y, Gd, Er)

The Mössbauer spectra of ferromagnetic RFe 11Ti and RFe 11TiH x ( R = Y , Gd, Er, x = 0 , 1) have been investigated in the temperature range 20–300 K and analysed in terms of a new model which allows a better fit of the spectra using less constraints than previously reported analyses. In addition to the dependence of magnetic hyperfine field and isomer shift on the number of Ti nearest-neighbours (NN) of the Fe atoms, this new model also considers the effect of the average interatomic distances between Fe atoms on the 8i, 8f and 8j crystallographic sites. Magnetic hyperfine fields were found to decrease with the average interatomic distances for Fe atoms on the same sites and with the same number of iron NN. This decrease was however lower than that due to the presence of one additional titanium NN. Furthermore the present model distinguishes the 8f from the 8j sites on the basis of the relative areas of the corresponding sextets. It leads to higher average magnetic hyperfine fields and isomer shifts for the 8f site as compared to the 8j sites which may be understood on the basis of electronic charge transfer between the rare-earth and Fe atoms. The dependence of hyperfine parameters on the number of titanium NN and on hydrogenation is similar to those previously reported.

Structural and magnetic phase formation in nanophase brass—iron electron compounds

Starting with Cu0.65Zn0.35 with an e/a ratio of 1.35 we studied the phase formation in nanophase (Cu0.65Zn0.35)1−xFex alloys in the concentration range 0.1 ≤x ≤0.7 to see the effect of altering the electron concentration. The evolution of bcc phase from the fcc phase as a function of Fe concentration was investigated by Mossbauer spectroscopy and X-ray diffraction. The grain size, lattice parameters, and average hyperfine magnetic field distributions were estimated for the nanophase alloys. The fcc phase was observed to persist up to 40 atomic per cent Fe substitutions, a mixed (fcc + bcc) phase region up to 70 atomic per cent Fe and bcc phase beyond 70 atomic per cent Fe. The magnetic state of the alloys changed from nonmagnetic forx ≤0.3 to magnetically ordered state at room temperature forx ≤0.33, which lies in the fcc phase region. The fcc phase alloys of Fe with non-magnetic metals have very low magnetic transition temperatures. However, in this system the room temperature state is unusually magnetic

Structure, phase composition and magnetic properties of mechanically alloyed and annealed quasibinary Fe(70)Si( x)C(30 − x) alloys

It has been demonstrated that mechanical alloying of the powder mixtures Fe(70)Si( x)C(30 − x) with 5 ≤ x ≤ 20 at.% results in the formation of an amorphous single phase, whose magnetic properties do not depend on x: an average hyperfine magnetic field H ¯ = 225 kOe (77 K), an average magnetic moment per Fe atom m ¯ Fe = 1.7 μ B (77 K), Curie temperature T c = 590–620 K, coercivity H c = 25 Oe (300 K). Only the ternary chemical compound, Fe 5SiC iron silicon carbide, has formed within the Fe–Si–C system after mechanical alloying followed by annealing (500 °C, 1 h), with its greatest quantity (95 wt.%) being in the Fe(70)Si(14)C(16) sample. The Fe 5SiC silicon carbide has an orthorhombic lattice ( Cmc2.1 space group symmetry ) with the parameters of a = 1.0043 nm, b = 0.7944 nm, c = 0.7469 nm. The lattice includes six nonequivalent local configurations of Fe-atoms. Fe 5SiC is a ferromagnet with T c = 780 K, m ¯ Fe = 1.77 μ B (77 K), H ¯ = 240 kOe (77 K), H c ≈ 450 Oe (300 K).

Structure, hyperfine interactions and magnetization studies of mechanically alloyed Fe 50Ge 50 and Fe 62Ge 38

X-ray diffraction, Mössbauer spectroscopy and magnetization measurements were used to study the structure and some magnetic properties of Fe 50Ge 50 and Fe 62Ge 38 prepared by mechanical alloying from the elemental powders. In both cases in the early stages of milling the intermediate paramagnetic FeGe 2 phase was formed. The mechanical alloying process of Fe 50Ge 50 resulted in the formation of the paramagnetic FeGe (B20) phase with an average crystallite size of about 15 nm. In the case of the Fe 62Ge 38, the ferromagnetic Fe 5Ge 3 (β) phase with a Curie temperature of about 430 K was obtained. The average crystallite size was about 9 nm. The average hyperfine magnetic field of about 16 T allowed it to determine that more than four germanium atoms exist in the nearest environment of the 57Fe isotopes in the Fe 5Ge 3 phase.

Phase changes in Fe72−x Al28Cr x (x = 0,2,4,6) alloys due to mechanical strain

Fe72−x Al28Cr x (x = 0,2,4,6) are made by arc melting a mixture of constituent elements in stoichiometric proportion, in argon atmosphere. The ingots so obtained are filed to make powder samples thereby giving them substantial mechanical deformation. It is observed that as-powdered samples show hyperfine field distribution typical of α-phase, where the atoms are randomly distributed on the available sites. Annealing at 900°C for 60 h leads to preferential occupation of lattice sites by the atoms and this results in better defined groups of hyperfine magnetic field (HMF) which can be associated with specific configuration in the neighbourhood of probe iron atoms. The average HMF is found to decrease sharply with increasing Cr concentration even though the net chromium concentration remains low (≤6 at%). The results show that cold working on samples is very important in changing the atomic ordering and must be taken into account if properties of equilibrium phases are probed.

Synthesis and characterisation of nanostructured FeCo alloys

Nanocrystalline Fe(1−x)Co x (x = 0.12, 0.5, 0.6) mixtures have been prepared by mechanical alloying using a planetary ball mill under several milling conditions. The alloying process between the elemental powders and the microstructure changes of the prepared samples have been investigated using X-ray diffraction (XRD) and 57Fe Mossbauer spectrometry. The XRD patterns refinement on the mechanical alloying products according to the Rietveld method (Maud software) reveals the allotropic transformation of Co from fcc to hcp form and the progressive dissolution of Co into the α-Fe lattice as a function of both Co concentration and milling conditions. The grain size values of the obtained powders reaches a nanometer scale of about 10 nm. Mossbauer results show that the beginning of the solid state reaction between Fe and Co elemental powders depends on the milling conditions. After 24 h of milling, the average hyperfine magnetic fields values of Fe88Co12, Fe50Co50 and Fe40Co60 mixtures are consistent with a disordered and an ordered FeCo solid solution, respectively.

Surface analysis of thin stainless steel films and thick-coated steel by simultaneous application of conversion electron and X-ray Mössbauer spectroscopy

A dual He/Ar gas counter for simultaneous measurements of conversion electron and X-ray Mössbauer spectra (CEMS and XMS) has been developed and applied to characterization of thin stainless steel films and thick-coated steel. For thin stainless steel films, three depth-selective CEMS spectra were simultaneously obtained by detecting the electrons with three different energy ranges (1 to 3 keV, 3 to 6.5 keV, and 6.5 to 12 keV). The iron oxide layer (4 nm in thickness) on stainless steel was clearly observed by detecting high-energy electrons (>6.5 keV). Ferromagnetic phase was produced by a magnetron Ar sputtering of austenitic stainless steel, and the average hyperfine magnetic field increased from 25 to 28 T by thermal treatment. The magnetic phase was partially converted into austenite (γ-phase) at 500 °C. In the case of thick-coated steel, where the coating was produced by electrochemical sulfurization, CEMS and XMS spectra were simultaneously obtained by detecting all the resonant electrons above 3 keV as well as X-rays between 3 and 6.5 keV. The area ratios of the subspectra assigned to the austenite and ferrite phases were different in the CEMS and the XMS spectra. This suggests that austenite and ferrite at the surface had selective reactivity with the sulfurizing agent. It was shown that the phase analysis of the surface, interface, and substrate was simply and effectively realized by using a dual He/Ar gas flow counter.

Structural properties of Fe 50Co 50 nanostructured powder prepared by mechanical alloying

Mechanical alloying of high purity elemental powders in a planetary ball mill (Fritsch pulverisette 7) was used to prepare nanocrystalline Fe and equiatomic FeCo powders. Morphology changes, structural properties and local iron environment variations have been investigated by Scanning Electron Microscopy, X-ray diffraction and 57 Fe Mössbauer spectrometry. X-ray diffraction profile fitting, reveals the Co allotropic transformation from fcc to hcp form at the early stage of milling. The milling route implies diffusion of hcp-Co into α (Fe) leading to the formation, after 12 h, of the bcc-FeCo solid solution with a lattice parameter close to a = 0.2861 nm and a grain size of about 12 nm. The analysis of the evolution of the hyperfine magnetic field distribution, indicates that the disordered bcc-FeCo solid solution is formed after 12 h of milling, through the interdiffusion of Fe and Co elemental powders. The average hyperfine magnetic field of the bcc-FeCo solid solution ( B = 35 T) suggests that the disordered Fe 50Co 50 system is formed.

Mössbauer and structural studies of Fe 0.7− x V x Si 0.3 alloy system

X-ray diffraction patterns for Fe0.7−xVxSi0.3 (x = 0, 0.05, 0.1, 0.15, 0.2, and 0.3) yield a single BCC-type phase for small values of x and a minor non-cubic phase starts to develop for large values of x. The lattice parameter is found increase with increasing vanadium concentration. Mossbauer experiments were made at room temperature and 20 K. Room temperature spectra show magnetic order for x = 0, 0.05, and 0.1, a central paramagnetic line of high intensity superimposed to the magnetically ordered component for x = 0.15, and a almost completely paramagnetic state for x = 0.2 and 0.3. A similar behavior prevails at 20 K, except that hyperfine splittings are larger and the magnetic ordering starts to show up for x = 0.2 and 0.3. In data analysis, each room-temperature and 20-K spectrum is fitted with a distribution of hyperfine sextets. The results clearly indicate the expected atomic disorder in the materials. The average magnetic hyperfine field is found to decrease with increasing x, reflecting the replacement of magnetic iron by nonmagnetic vanadium. The average isomer shift shows the same vanadium-concentration dependence. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Mössbauer study of FeCoSiAlGaPCB amorphous alloys

A Mössbauer spectrometry and magnetic study have been performed on FeCoSiAlGaPCB amorphous alloys in order to get information about the variations in the atomic short range order with the substitution of Fe by Co. The decrease of the Curie temperature with decreasing Fe content was analyzed in the framework of the molecular field theory. The average hyperfine magnetic field at 77 K decreases linearly with increasing Co content as does the average magnetic moment per transition metal atom and a linear dependence between both quantities is found. The standard deviation of the hyperfine magnetic field distribution at 77 K does not change with Fe substitution and the average isomer shift increases linearly with the Co content of the alloy. The hyperfine magnetic field distributions show a bimodal character that evidences the presence of two types of Fe environments in the as-cast alloys.

Mössbauer Studies of Fe0.7-xSi0.3MnxAlloys

In this work we present Fe57 Mossbauer study for the alloy system Fe0.7− x Si0.3Mn x , where 0 ≤ x ≤ 0.3. Mossbauer spectroscopic results show that all the samples studied are magnetically ordered at 77 K, and at room temperature, except for x = 0.3 at 300 K where it shows paramagnetic behavior. The average magnetic hyperfine field is found to decrease with increasing the manganese concentration at 77 K and 300 K. The average magnetic hyperfine field is found to increase with decreasing the temperature from 300 K to 77 K for all samples under investigation. The average isomer shift is found to decrease with increasing the manganese concentration.

A study of Mssbauer spectroscopy of microcrystallization of amorphous Fe7 3.5Cu1Nb3Si13.5B9 irradiated b y a CO2-Laser

Microcrystalline phases were produced by laser irradiation on the Fe73.5Cu1Nb3Si13.5B9 amorphous ribbon with a power ranging from 40 to 170W,scaning speed 10mm/s,laser beam spot 20mm. Hyperfine structures of the original and crystallized samples were analyzed by transmission Mssbauer spectros copy. We discovered that the basic parameters of the Mssbauer spectra——isome r shift（IS）, quadrupole splitting（QS） and hyperfine magnetic field（Hhf） ch ange with the laser power. Experimental results show that the magnetic moment re organization of Fe73.5Cu1Nb3Si13.5 B9 amorphous phases has take n place and the atom magnetic moment direction maintains a preferred in-plane or ientation, The average hyperfine magnetic field of the amorphous phase is improv ed because of the microcrystalline phase. The crystallized phase was Fe-Si alloy with a DO3 structure, and the area of its spectral lines is about 2% —3.4%. This is caused by the jump of one electron in Fe atom 3d6 shell int o Si atom 3p2 shell, forming a stability electron group.

Influence of nitrogen on the magnetovolume effects in La(FexAl1−x)13 compounds

Nitrogen and hydrogen absorptions have been carried out in order to discuss the influence of interstitial atoms on the magnetovolume effects for the La(FexAl1−x)13 (x=0.83 and 0.86) compounds. The average magnetic hyperfine field and the Curie temperature TC of nitrides are lower than that of hydrides. The volume expansion due to the nitrogen absorption is about twice that due to the hydrogen absorption. Comparing the change in TC of the nitrides with that of hydrides and the pressure effect on TC, the hybridization between the Fe 3d and N 2p orbital should be taken into consideration in the lower TC of nitrides.

On the particle size dependence of the magnetic anisotropy energy constant

Mössbauer spectroscopy is used to study a system of Fe 3O 4 fine particles (12.6 nm) at temperatures from room temperature down to 5 K. The Mössbauer spectra were fitted with field distributions and the average hyperfine magnetic field is found to decrease with increasing temperature. Using the collective magnetic excitation model, the effective magnetic anisotropy energy constant, K, is estimated as 0.78×10 5 J/m 3. This value is lower than that obtained by others for systems with smaller sizes, which is consistent with the dependence of the magnetic anisotropy energy constant on the particle size.