Mean Hyperfine Magnetic Field Research Articles

Microstructure Evolution and Mossbauer Spectroscopy Research of Nanostructured Ni3 Fe Intermetallic

Nanocrystalline Ni75Fe25 (Ni3Fe) powders were prepared by mechanical alloying process using a vario-planetary high-energy ball mill. The intermetallic Ni3Fe formation and different physical properties were investigated, as a function of milling time, t, (in the range 6 to 96 h range), using X-Ray Diffraction (XRD) and Mössbauer Spectroscopy techniques. X-ray diffraction were performed on the samples to understand the structural characteristics and get information about elements and phases present in the powder after different time of milling. The refinement of XRD spectra revealed the complete formation of fcc Ni (Fe) disordered solid solution after 24 h of milling time, the Fe and Ni elemental distributions are closely correlated. With increasing the milling time, the lattice parameter increases and the grains size decreases. The Mössbauer experiments were performed on the powders in order to follow the formation of Ni3Fe compound as a function of milling time. From the adjustment of Mössbauer spectra, we extracted the hyperfine parameters. The evolution of hyperfine magnetic field shows that the magnetic disordered Ni3Fe phase starts to form from 6 h of milling time and grow in intensity with milling time. For the milling time more than 24 h, only the Ni3Fe disordered phase is present with a mean hyperfine magnetic field of about 29.5 T. The interpretation of the Mossbauer spectra confirmed the results obtained by XRD.

Nickel-doped nanostructured Fe70Al30 alloys: The role of Ni on the microstructure and the evolution of hyperfine and magnetic properties

We have investigated the effect of the Nickel concentration on the crystal structure and microstructure, as well as on the hyperfine and magnetic properties of nanostructured (Fe0.7Al0.3)100-xNix powders (x = 0, 5, 10 and 15 at.%) fabricated by mechanical alloying. After 72 h of milling, all the Fe(Al, Ni) samples are single-phase disordered solid solutions with body centred cubic crystal structure. A progressive reduction of the lattice parameter value from 2.9084 Å for the Ni-free FeAl binary alloy down to 2.8897 Å for the x = 15 ternary compound is observed. The mean grain size of the nanocrystals also diminishes down to c.a. 20 nm as the Ni concentration is increased, whereas the mechanically-induced microstrain remains almost constant at around 0.5%. The magnetic measurements show a ferromagnetic character of all the samples at room temperature with a slight decrease of both saturation magnetization and coercivity as the Ni concentration rises. The fit of Mössbauer spectra collected at room temperature gives an almost constant value (around 26 T) for the mean hyperfine magnetic field, <Bhf>(T). Hence, the addition of Ni to Fe (Ni,Al) solid solution has not a clear influence on the value of <Bhf>, although the hyperfine field distributions suggest somewhat different local environments of Fe atoms.

Systematic study of the dependence of magnetic and structural properties of Nd2Fe14B powders on the average particle size

A systematic study of the magnetic and structural properties dependence on the particle size was realized. For this, commercial NdFeB powder was separated into five different mean particle sizes using sieves. Besides, from the original powder, eleven samples were also produced by mechanical milling assisted by surfactant, using various milling times. A total of sixteen samples were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), vibrating sample magnetometry (VSM), and Mössbauer spectrometry (MS). The particle sizes of the samples vary from the micrometer to the nanometer scale. The crystallite size decreases with decreasing particle size. XRD result indicates that the Nd2Fe14B phase is found in all the samples, and the presence of this phase is also corroborated by MS using six sextets for fitting their spectra, with an additional singlet corresponding to the Nd1.1Fe4B4 phase. The mean hyperfine magnetic field increases with increasing particle size because the magnetic dipolar interaction between the magnetic moment of the particles increases with particle size. From the VSM measurements the magnetic energy density (BH)max values were calculated for different particle sizes, and their maximum value of 34.45 MGOe is obtained for the sample with the particle size of 60 μm.

Structural, magnetic, and mechanical hardness characterization of the alloy Nd16(Fe76−xNix)B8 with x = 0, 10, 20, and 25

In this work, samples of the alloy Nd16 (Fe76−x Nix) B8 with x = 0, 10, 20, and 25 were produced by arc melting under an Ar atmosphere and heat treated at 1073 K during 30 min, and then quenched in ice–water mixture. X-ray diffraction (XRD), Mossbauer spectroscopy (MS), and vibrating sample magnetometry (VSM) were used to characterize the properties of the obtained samples. Microhardness tests were performed too. XRD results found Nd2Fe14B and Nd1.1Fe4B4 as main phases. It is found for x = 0, 10, 20, and 25, lattice parameters a and c, and the volume of Nd2Fe14B and Nd1.1Fe4B4 phases, which decrease with the increase of nickel content. The parameter a of the Nd1.1Fe4B4 phase has a tendency to increase in value compared to the parameter c which has a tendency to decrease with the concentration of nickel; this behavior causes the lattice to dilate in a and it is compressed in c, indicating that Ni atoms are preferably entering along c. The two phases parallel to crystallite sizes are greater than the perpendicular ones, indicating that the crystallite shape is not spherical but elongated in that direction. XRD results for all samples doped with Ni indicate that the crystallite sizes are of the nanometer order and range between 5 and 90 nm. It is evident the addition of this element does not damage the structural formation of Nd2Fe14B phase. MS shows seven magnetic sites (16k1, 16k2, 8j1, 8j2, 4c, 4e, and sb d) and a paramagnetic phase (doublet) corresponding to the phases found by XRD. The mean hyperfine magnetic field of the samples decreases with the increase in the concentration of Ni. According to the decrease of the percentage of the area and the hyperfine magnetic field of 16k2, 8j2, and 4c sites’ phase Nd2Fe14B in Ni-doped samples, preference of nickel atoms to replace iron atoms at these sites was established. It can see also the relative area of the site d (Nd1.1Fe4B4) which decreases with Ni concentration. VSM results showed that the major phase Nd2Fe14B is the hard magnetic phase, while the paramagnetic phase Nd1.1Fe4B4 is the minority phase. There is a general trend of microhardness increase with nickel content, attributable to nickel doping which reduces the lattice parameters and porosities in the sample improving its hardness.

Theoretical and experimental comparative study about magnetic behavior of Fe-Al alloys in the high Fe concentration region

In this research, annealing samples of Fe100-qAlq (with q ≤ 600/32; Δq = 100/32) were obtained by arc-melting. These were heat treated at 1000 °C during a week followed by quenching in ice water. The ferromagnetic iron matrix was modified with the non-magnetic Al atom. These samples were analyzed by X-ray diffraction and Mössbauer spectroscopy at room temperature. All alloys present disordered body centered cubic (BCC) structure or A2 with mean crystallite sizes of about 34 nm. It was observed that when q = 3.125% the iron's hardness falls over 80%. Furthermore, Mössbauer spectroscopy shows that all alloys are disordered and ferromagnetic. The spectra were fitted using a hyperfine magnetic field distribution with ΔH = 1T. Statistical and hyperfine parameters of the distributions were obtained as a function of q. After fixing the Mössbauer spectra, it was found that the mean hyperfine magnetic field (MHMF) presents a linear decrease with the Al concentration. This behavior is strongly related with the diluted character of the impurity. Through Mössbauer spectroscopy and/or X-ray diffraction, an anomalous behavior was observed around q = 12.500. Moreover, by using the Monte Carlo method and the local environment model, the long-range order parameter of the samples was possible to obtain. Additionally, only 2 samples reached the perfect disorder, which indicated that the method of preparation does not guarantee the state of perfect disorder. The local environment model allowed finding the variations in the hyperfine field of the Fe when one atom of Fe is replaced by one Al atom in the first or second coordination shell of the 57Fe. Finally, the Monte Carlo method with Metropolis dynamics and the ½ Ising model were used to simulate the magnetic behavior of the alloys, used in this study. The results were compared with experimental phase diagrams of these alloys, allowing us to find the functionality of the exchange energy in the system as a function of Al concentration. For this system, the phase diagram was fitted using a cubic function of the JFeFe exchange energy with the aluminum concentration.

Comparative Magnetic and Structural Properties Study of Micro- and Nanopowders of Nd2Fe14B Doped with Ni

Micropowders of melted and heat-treated Nd16(Fe76−xNix)B8 alloys system, with x = 0, 10, 20, and 25 (size distribution under 20 μm), were studied and compared with the study of nanopowders obtained, from the previous ones, by surfactant-assisted ball-milling process during 2 h. By XRD, a majority of Nd2Fe14B hard phase and a minority of α-Fe, Nd1.1Fe4B4 and NdNi2 phases were detected. The last one increases with Ni content. The crystallite size of the hard phase, in both types of samples, is not affected by the Ni content; however, the grains in micropowders are oblate, with a mean size of 37 nm, while those of the nanopowders are symmetric, with a mean size of 35 nm. Mossbauer spectra were fitted with seven sextets, which correspond to the six ferromagnetic sites of the hard phase and that of the α-Fe, and a doublet corresponding to the paramagnetic Nd1.1Fe4B4 phase. The mean hyperfine magnetic field, for both types of samples, decreases with Ni content. The hysteresis loops of both types of samples show a hard magnetic character, however, the coercive field and the Mr/Ms values for nanopowders are greater than those obtained for micropowders for all the Ni contents. Values of Hc = 2 kOe and Mr/ Ms = 0.54 were obtained for nanopowders with 10 at.% Ni. From the hysteresis loops, which include the initial magnetization curve, Henkel plots for all the samples were obtained. These plots show that for micropowders, the predominant magnetic interaction is of dipolar type, while for nanopowders, the ferromagnetic exchange is the predominant one, which favored the magnetization.

Elaboration, Structure and Mössbauer Spectroscopy of Nanostructured Fe100−xSix Powders Elaborated by Mechanical Alloying

We have studied the effect of the silicon concentration on the structural and hyperfine properties of nanostructured Fe[Formula: see text]Six powders ([Formula: see text], 20, 25 and 30[Formula: see text]at.%) prepared by mechanical alloying. The X-ray diffraction (XRD) studies indicated that after 72[Formula: see text]h of milling, the solid solution bcc-[Formula: see text]-Fe(Si) is formed. The grain sizes, [Formula: see text]D[Formula: see text] (nm), decreases with increasing Si concentration and reaches a minimum value of 11[Formula: see text]nm. We have found that the lattice parameter decreases with increasing Si concentration. The changes in values are attributed to the substitutional dissolution of Si in Fe matrix. From the adjustment of Mössbauer spectra, we have shown that the mean hyperfine magnetic field, [Formula: see text]H[Formula: see text] (T), decreases with increasing Si concentration. The substitutional dependence of [Formula: see text]H[Formula: see text] (T) can be attributed to the effect of p electrons Si influencing electrons d of Fe.

Structural and magnetic properties of FeCoC system obtained by mechanical alloying

Fe96−XCoXC4 (x = 0, 10, 20, 30, 40 at. %) alloys were obtained by mechanical alloying of Fe, C and Co powders using high-energy milling. The structural and magnetic properties of the alloy system were analyzed by X-ray diffraction, Scanning Electron Microscopy (SEM), Vibrating Sample Magnetometer (VSM) and Mossbauer Spectrometry at room temperature. The X-ray diffraction patterns showed a BCC-FeCoC structure phase for all samples, as well as a lattice parameter that slightly decreases with Co content. The saturation magnetization and coercive field were analyzed as a function of Co content. The Mossbauer spectra were fitted with a hyperfine magnetic field distribution showing the ferromagnetic behavior and the disordered character of the samples. The mean hyperfine magnetic field remained nearly constant (358 T) with Co content.

Evidence of Dipolar Magnetic Interaction in Melted Fe50Al50 Samples

Powders of the Fe50Al50 melted and heat treated samples were separated at different mean particle sizes as well as characterized based on their structural and magnetic properties. All the samples, except that with biggest particle size, showed Fe-Al BCC and α-Fe phases as well as the same nanostructure. The powder with the biggest particles, with particle size bigger than 105 μm, presents the additional minority presence of FeO and Al2O phases. The powders were found to be ferromagnetic at room temperature with a mean hyperfine magnetic field (MHMF) that increases with increasing particle size. The origin of the increase of the MHMF is attributed to the increment of the magnetic dipolar interactions between the magnetic moment of each particle and the field produced by other magnetic moments of their surrounded particles. This field also increases as the particle size increases. Besides the dipolar magnetic interaction between particles, the Fe-Al and α-Fe grains present a ferromagnetic coupling between them.

Low temperature study of mechanically alloyed Fe67.5Ni32.5 Invar sample

The study at low temperatures of powder of the Invar alloy, Fe67.5Ni32.5, produced by mechanical alloying, shows that the sample presents two structural phases, the Fe–Ni BCC and the Fe–Ni FCC. The 57Fe Mössbauer spectra obtained in this sample at different temperatures were fitted considering two hyperfine magnetic field distributions. The first one having the larger mean field and only one peak (at ca. 35T, varying with T), is associated with the BCC phase, and the second one, presenting several broad peaks (distributed between 10 and 35T), is associated to the FCC phase. A singlet, which is associated to low spin Fe sites of the FCC phase, was also considered. The mean hyperfine magnetic field of the BCC phase increases monotonically as temperature decreases, while that of the FCC phase presents an anomaly near 75K. The real part of the ac magnetic susceptibility temperature scans presents a peak whose position increases from 31 to 39K, when the ac field frequency increases from 100 to 5000Hz. These results permit to associate the detected anomaly to the occurrence of a reentrant spin glass transition.

Mean hyperfine fields at 57Fe in dilute iron-based alloys studied by Mössbauer spectroscopy

Abstract The room temperature Mössbauer spectra of 57Fe were measured for numerous dilute iron-based alloys Fe1− x D x (D = Al, Co, Cr, Mn, Mo, Ni, Os, Pt, Re, Ru, Ta, Ti, V, W, Zn), annealed at 1270 K for 2 h before the measurements. The spectra were analyzed using the Hesse–Rübartsch method in order to determine the mean hyperfine magnetic field &lt;B&gt; at the 57Fe nuclei as a function of concentration x of the minority component of the alloy. As the binary alloys are one-faze solid solutions of an element D in iron, a linear relationship between &lt;B&gt; and x is observed. The result supports the suggestion that Mössbauer spectroscopy is a useful tool for the study of dissolution of different elements in iron.

Hyperfine interactions in R x Gd1− x Fe3 intermetallics R = Tb, Y

The structural and magnetic properties of rare earth iron intermetallic compounds TbxGd1−xFe3 and YxGd1−xFe3 (x = 0. 0, 0. 1, 0. 2, 0. 4, 0. 5, 0. 6, 0. 8, 1. 0) was studied by X-ray diffraction, the 57Fe Mossbauer effect and SQUID measurements. All investigated compounds crystallize in the rhombohedral PuNi3-type of crystal structure. The investigation of magnetic properties of RxGd1−xFe3 proved their ferrimagnetic behavior. The Curie temperature of the investigated compounds decreases with the increase of R concentration from 721K (GdFe3) to 655K (TbFe3) and 533K (YFe3). The saturation magnetic moment MS in the RxGd 1−xFe3 system increase with x parameter. The Mossbauer spectra are analyzed using four sextets, corresponding to three crystallographically (b, c, h) and four magnetically (b, c, h1, h2) inequivalent sites for iron. The mean hyperfine magnetic field increases with increase of the Gd concentration

Magnetism influenced by structural disorder in melt-spun DyMn6 − x Ge6 − x Fe x Al x (x = 2.5, 3)

Different chemical and/or geometrical orders were found in melt-spun DyMn6 − xGe6 − xFexAlx with x = 2.5 and 3 having fully amorphous and mixed (crystalline and amorphous) structure, respectively. Thermal variations in magnetization M from liquid helium up to room temperature for both samples are similar. Magnetization value at zero field cooled curve reaches about 0.1 μB per formula unit at 2 K and then increases. Two maxima are visible, the first at 50 K (a sharp effect) and the second very broad ranging from 150 to 200 K. 57Fe Mossbauer spectrometry investigation revealed a remaining magnetic component in addition to a prevailing quadrupolar feature. Application of a weak external magnetic field causes an increase in the mean hyperfine magnetic field Bhyp and the volume fraction of magnetic component. This observation was confirmed by results of M(T), M(H) and AC magnetic susceptibility measurements. In short-range ordered crystallographic zones characteristic of melt-spun DyMn6 − xGe6 − xFexAlx (x = 2.5, 3) alloys, the related magnetic ordering, called the mictomagnetism or the cluster spin glass appears.

Evidence of dipolar magnetic field in mechanically alloyed Fe50Al50 samples

Powders of mechanically alloyed Fe50Al50 were milled during 72h and separated at different mean particle sizes as well as characterized based on their structure and magnetic properties. All the samples showed Fe–Al BCC and α-Fe phases as well as the same nanostructure. Fe50Al50 powders were found to be ferromagnetic at room temperature with a mean hyperfine magnetic field that increases with increasing particle size. The origin of these magnetic behaviors is attributed to the increment of magnetic dipolar interactions between the magnetic moment of each particle and the field produced by other magnetic moments of their surrounded particles. This field also increases as the particle size increases.

Comparative study between melted and mechanically alloyed samples of the Fe50Mn10Al40 nanostructured system

Nanostructured powders of melted and 48 h-mechanically alloyed (MA) samples of the Fe50Mn10Al40 system were studied by XRD, SEM and Mossbauer spectroscopy (MS), and their properties were compared. The samples present BCC structure with similar mean lattice parameter (near 2.92 A) and grain size (around 22 nm). The MA sample presents additionally the α-Fe phase. Mossbauer spectra of the samples present a hyperfine field distribution (HFD), a broad paramagnetic (P) site and a sextet showing that the BCC ternary phase is disordered with Fe sites in environments rich in Fe (HFD) and rich in Al and Mn (P), respectively. The mean hyperfine magnetic field vs. temperature curve of melted sample presents two kinks, one at 28 K and other at 210 K and a Curie temperature at 340 K. A similar curve is observed for the milled sample but the kinks occur at 65 and 265K. Mossbauer spectra at different temperatures with and without applied field permit to conclude that the low temperature anomaly corresponds to the freezing temperature of a re-entrant spin-glass phase (RSG) and that of the second one corresponds to a blocking temperature of a superparamagnetic (SP) phase. These phases are possible in the samples due to their disordered character induced by the preparation conditions and the competitive interactions of the Fe and Mn atoms. The enhancement of the magnetic behaviour of the MA sample is due its larger disorder induced by the preparation method that can also explain the increase of the RSG and SP transition temperatures.

Epitaxial growth, magnetic properties, and lattice dynamics of Fe nanoclusters on GaAs(001)

Epitaxial bcc-Fe(001) ultrathin films have been grown at $\ensuremath{\sim}50\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ on reconstructed $\mathrm{Ga}\mathrm{As}(001)\text{\ensuremath{-}}(4\ifmmode\times\else\texttimes\fi{}6)$ surfaces and investigated in situ in ultrahigh vacuum (UHV) by reflection high-energy electron diffraction, scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and $^{57}\mathrm{Fe}$ conversion electron M\ossbauer spectroscopy (CEMS). For ${t}_{\mathrm{Fe}}=1$ ML (monolayer) Fe coverage, isolated Fe nanoclusters are arranged in rows along the [110] direction. With increasing ${t}_{\mathrm{Fe}}$ the Fe clusters first connect along the $[\ensuremath{-}110]$, but not along the [110] direction at 2.5 ML, then consist of percolated Fe clusters without a preferential orientation at 3 ML, and finally form a nearly smooth film at 4 ML coverage. Segregation of Ga atoms within the film and on the Fe surface appears to occur at ${t}_{\mathrm{Fe}}=4$ ML, as evidenced by XPS. For coverages below the magnetic percolation, temperature-dependent in situ CEMS measurements in zero external field provided superparamagnetic blocking temperatures ${T}_{B}$ of $62\ifmmode\pm\else\textpm\fi{}5$, $80\ifmmode\pm\else\textpm\fi{}10$, and $165\ifmmode\pm\else\textpm\fi{}5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for ${t}_{\mathrm{Fe}}=1.9$, 2.2, and 2.5 ML, respectively. At $Tl{T}_{B}$, freezing of superparamagnetic clusters is inferred from the observed quasilinear $T$ dependence of the mean hyperfine magnetic field $⟨{B}_{hf}⟩$. By combining the STM and CEMS results, we have determined a large magnetic anisotropy constant of $\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ and $\ensuremath{\sim}8\ifmmode\times\else\texttimes\fi{}{10}^{5}\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕{\mathrm{m}}^{3}$ at ${t}_{\mathrm{Fe}}=1.9--2.2$ and 2.5 ML, respectively. For ${t}_{\mathrm{Fe}}\ensuremath{\leqslant}2.5$ ML, our uncoated ``free'' Fe clusters exhibit intrinsic magnetic ordering below ${T}_{B}$, contrary to literature reports on metal-coated Fe clusters on GaAs. Our present results demonstrate that the nature of the percolation transition for free Fe nanoclusters on GaAs(001) in UHV is from superparamagnetism to ferromagnetism. From the M\ossbauer spectral area, a very low Debye temperature ${\ensuremath{\Theta}}_{D}$ of $196\ifmmode\pm\else\textpm\fi{}4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is deduced for these uncoated Fe nanoclusters in UHV, indicating a strong phonon softening in the clusters.

Mössbauer study of nanocrystalline PrFeB and PrFeCrB alloys

Ribbons of Pr 4.5Fe 77B 18.5 and Pr 5Fe 74Cr 3B 18 alloys were produced by melt spinning and then annealed by flash or conventional annealing to develop enhanced-remanence nanocrystalline magnetic material. These materials were studied by magnetic measurements, X-ray diffraction and Mössbauer spectroscopy in order to understand the relationship between structural and magnetic properties. These analyses showed that the phases present in these materials are Pr 2Fe 14B, Fe 3B and α-Fe. The samples with Cr present a coercive field 50% higher than the Cr-free samples. The Mössbauer spectra were analyzed as a superposition of the well-known spectra of Pr 2Fe 14B, Fe 3B and α-Fe. The mean hyperfine magnetic field of each phase was obtained from the spectral analysis, as well as, the relative amount of each phase present. From Mössbauer results it seems that Cr atoms preferentially dissolves in the Fe 3B phase.

&lt;SUP&gt;57&lt;/SUP&gt;Fe M&amp;ouml;ssbauer Study on Distribution and Interaction of N Interstitials in &amp;gamma;-FeN Austenite and &amp;alpha;&amp;prime;-FeN Martensite

N atoms occupy interstitial sites in α- and γ-Fe and affect the physical and chemical properties of Fe. In order to clarify the distribution of N atoms in α- and y-Fe and the influence upon Fe, 57 Fe Mossbauer measurements have been performed for Fe-N austenite and martensite. In γ-FeN austenite, there are three kinds of Fe atoms with zero, one and two N atoms as near neighbors. An Fe atom and two near neighbor N atoms in γ-Fe constitute a N-Fe-N 180°-linear chain, although such a configuration cannot be observed in Fe-Ni-C austenite. From the amounts of these components, it was confirmed that the distribution of N atoms in γ-Fe is not random and the repulsive force acts between near neighbor N atoms. By comparison with Fe-Ni-C austenite, it became clear that the repulsive force between N atoms is weaker than that between C atoms. It was also confirmed that the martensitic transformation from γ-to a'-phase can be induced by applying the magnetic field. This phenomenon occurs at the critical magnetic field which depends on N content and increases with N content. The 57 Fe Mossbauer spectrum of α'-FeN martensite can be analyzed by four magnetic components which correspond to Fe as the first, second, third and further near neighbors of the interstitial N atom. Among them, the third near neighbor Fe shows a large hyperfine magnetic field, 36 T at room temperature, but the mean hyperfine magnetic field of α'-FeN martensite is nearly equal to that of α-Fe. Although the amounts of the first and second near neighbor Fe atoms can be explained by assuming that N atoms randomly occupy the O 2 sites in the bct lattice, the amounts of the third and the further near neighbors Fe cannot. This may be because of the diffusion of N atoms to form the N-rich region in the matrix at room temperature.

Hyperfine fields, local environment effects and site preference in Fe 3- xCr xAl alloys

The properties of Fe 3− x Cr x Al ( x = 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5) alloys with DO 3-type of ordering have been investigated by Mössbauer spectroscopy at room temperature without and with external magnetic field parallel to the beam direction. The results show that the mean hyperfine magnetic field decreases nonlinearly with chromium concentration and is linearly correlated with the average magnetic moment of the sample under study. The postulated quadratic dependence of h.m.f. on the number of nearest Fe neighbours allows one for unambiguous identification of all the components of the measured spectra. Hyperfine magnetic field, isomer shift and iron magnetic moment are presented as functions of local environments of iron atoms. The analysis of the site occupations showed that chromium atoms occupy preferentially B sites, the effect expected but not found in isostructural Fe 3− x Cr x Si alloys [1].

Local environments effects and site preference in Fe3−xCrxAl alloys

The properties of Fe 3− x Cr x Al alloys for x ≤ 0.5 with DO 3 -type of ordering have been investigated at room temperature by Mössbauer spectroscopy in zero field and in external magnetic field of about 4.3 kOe applied along the beam direction. The results show that the mean hyperfine magnetic field (h.m.f.) decreases nonlinearly with Cr concentration and is linearly correlated with the average atomic magnetic moments of the samples. The postulated quadratic dependence of h.m.f. on the number of nearest neighbour (n.n.) iron atoms allows unambiguous identification of the components of the measured spectra. The analysis of relative intensities of every component leads to the conclusion that Cr preferentially occupies B-sites. The values of iron magnetic moment as a function of n.n. configuration are estimated for both (A,C) and B sites.