The magnetic hyperfine interaction of iron atoms isolated in a xenon matrix in the presence of an external magnetic field

The Mössbauer effect has been used to measure the magnetic hyperfine interaction of isolated ⁵⁷Fe atoms in solid xenon with an applied external magnetic field. A field dependent Mössbauer absorption spectrum is observed. The ground state of these iron atoms is a triplet, which is split in the external field. The Mössbauer spectrum was analyzed taking into consideration relaxation effects. For an applied external field of 28 kOe an internal magnetic field at the ⁵⁷Fe nucleus of 700± 15 kOe was observed (external field included).     

Magnetic hyperfine fields at Fe,Cd and Sn sites in an FeCo alloy

The magnetic hyperfine field at an Fe site in the ferromagnetic alloy Fe_0.475Co_0.525 was measured using the Mössbauer effect. The value obtained at room temperature was 343 kOe. The hyperfine field at a substituted Cd impurity was measured by the method of time differential perturbed angular correlations. A single frequency was observed at room temperature, corresponding to a field of -177 kOe. Using the Mössbauer effect, the Sn site hyperfine field was measured in a sample in which 0.3 atomic percent of ¹¹⁹Sn had been substituted. The room temperature spectrum consisted of the superposition of a single line, together with a six-line hyperfine spectrum, corresponding to a field of 231 kOe. A phenomenological interpretation is proposed for Fe, Cd and Sn fields in the binary alloys of iron.     

Magnetic properties of the garnets Bi0·8Ca2χT2·2-2.χFe5-χVχ]O12

The behaviour of the magnetization, Curie temperature, Mössbauer spectra, and lattice parameter is studied in the garnet series Bi_0·8Ca_2.χT_2·2-2.χFe_5-χV_χ]O₁₂. The shape of magnetization vs temperature curves shows only a minor dependence on x. The hyperfine field at the octahedral ⁵⁷Fe nuclei at 5°K decreases linearly with x (12·5kOe per substituted V neighbour), while that at the tetrahedral ⁵⁷Fe nuclei is not affected. The dependence of the Curie temperatures and hyperfine fields on x is discussed in relation to the Fe-O-V-O-Fe exchange. The influence of Bi substitution is consistent with the idea of a geometric effect.     

Mössbauer experiments on57Fe in the giant moment system Ni75-x Fe x Ga25

Mössbauer experiments on⁵⁷Fe on the giant moment system Ni_75-x Fe _x Ga₂₅ were performed. For various Fe concentrationsx the hyperfine fields, the isomeric shift, and the quadrupole splitting were measured. A saturation hyperfine field of 223 (2) kOe at the Fe atom substituting a Ga site and of 200 (2) kOe at the Fe atom substituting a Ni site were found.     

Hyperfine field of Lu in Fe and Ni and annealing properties of the FeYb implanted alloy

Integral perturbed angular correlation measurements of the hyperfine field at ¹⁷⁵Lu isotope-separator implanted in Fe and Ni yield fields of −(575 ± 41) kOe and −(130 ± 27) kOe, respectively. A clear annealing stage is found around 450°C.     

High magnetic field behavior of iron impurities in chromium

Mössbauer measurements in ⁵⁷Fe in dilute FeCr alloys in external magnetic fields up to 140 kOe are presented. The magnetic hyperfine interactions are compared with results obtained by Herbert, Clark and Wilson and are discussed in terms of a model due to Housley and Dash.     

Mössbauer effect study of charge and spin transfer in Fe-Cr

The influence of temperature and time of annealing on hyperfine fields and isomer shifts has been studied for a range of Fe–Cr alloys containing 1–45 at% Cr. It has been revealed that up to 15at% Cr neither time nor temperature of annealing practically does affect the hyperfine parameters. For more concentrated samples, however, both temperature and time of annealing are important. In particular, the Mössbauer spectrum of Fe–45.5 at% Cr annealed at 700°C for 5 h was a single-line indicating that the sample was paramagnetic. The observed changes of the hyperfine fields and the isomer shifts have been interpreted in terms of a spin and charge trasfer, respectively.Strong linear correlations between the following quantities have been revealed: the hyperfine field H(0,0) and the isomer shift IS(0,0); the average hyperfine field $\text{H}$ and the average isomer shift $\text{IS}$; the average hyperfine field $\text{H}$ and the average number of Cr atoms in the first two coordination spheres, $\text{N}$. It has been calculated from the first two correlations that a) a change of polarization of itinerant s-like electrons of one electron is equivalent to a change of the hyperfine field of 1602 kOe, and b) on average, a unit change of s-like electron polarization is equivalent to 3277 kOe. The two constant are very close to theoretical estimations, which can be found in literature. Correlation between the hyperfine field and the isomer shift led to a conclusion that the substitution of Fe atoms by Cr ones decreases the density of spin-up electrons on average by 0.026 electrons per one Cr atom in a unit cell. These electrons are most likely trapped by Cr atoms, because the hyperfine field at neighbouring Fe nuclei decreases and the density of charge at those nuclei increases at the rate of 0.029 electrons per one Cr atom in a unit cell.Based on the results obtained, a formula describing the dependence of the average hyperfine field on Cr contents and on the heat treatment has been postulated for Fe–Cr alloys.     

57Fe and 166Er Mössbauer and magnetic studies of RFe4B (R = Er,Tm, Lu) compounds

Magnetic and Mössbauer studies have been carried out on a series of ternary borides RFe₄B (R = Er, Tm, Lu) which have the hexagonal CeCo₄B type structure. These compounds are found to be magnetically ordered at room temperature. Magnetization studies in the temperature range from 5 to 300 K reveal the presence of compensation temperatures in Er and Tm compounds and indicate antiferromagnetic coupling between the rare earth and Fe moments. Room temperature ⁵⁷Fe Mössbauer studies yield values of hyperfine fields at the two Fe sites as 246 and 185 kOe in ErFe₄B and TmFe₄B, and 204 and 145 kOe in LuFe₄B. The ¹⁶⁶Er Mössbauer studies give nearly free-ion hyperfine field at the Er sites which indicates that the exchange interaction in ErFe₄B is much stronger than crystal field interaction.     

Influence of Si on spin and charge density changes in bcc-iron

The influence of Si on the ⁵⁷Fe and ¹¹⁹Sn site hyperfine (hf) fields and isomer shifts has been studied for a series of Fe-Si alloys containing up to ca. 13 at% Si and ca. 0.9 at% ¹¹⁹Sn. The observed changes of the hf fields and the isomer shifts have been interpreted as reflecting spin and charge density changes, respectively. The following correlations could be established: hf field H(0,0) vs. isomer shift IS(0,0) of undisturbed atomic neighbour configurations (0,0), average hf field, H? vs. average isomer shift, $\text{IS}$; average hf field, H? vs. average number of Si atoms within the first two neighbour shells, N?. Based on the f correlations the following hf coupling constants have been determined: a) the hf coupling constant for s-like itinerant electrons are 690 kOe/s-el for Fe and 2100 kOe/s-el for Sn, b) the average hf coupling constants are 660 kOe/s-el and 2100 kOe/s-el for Fe and Sn, respectively. From the correlation between H? and N? the changes in the spin or charge densities caused be one Si atom per unit cell, η, have been deduced as follows: η(Fe)=0.17 and η(Sn)=0.03. Comparison is made with previously reported equivalent results for the Fe-Al system.     

NMR study of some heusler alloys containing Co and Mn

The⁵⁹Co and⁵⁵Mn NMR were measured at 4.2 K by spin echo technique. The hyperfine fields in Co₂ MnAl and Co₂MnSb were determined, and it was suggested that in the Co₂MnZ compounds the Co hyperfine field depends on Z. The magnitude of the hyperfine field at Mn dilutely dissolved in Co₂TZ by replacing T (T=Ti, V, Cr, Fe) was found to be larger by 30–80 kOe than that in Co₂MnZ with the same Z. The hyperfine field at Co dilutely dissolved in X₂ MnZ (X=Ni, Cu) by replacing X had a value quite near to that in Co₂MnZ.     

Nuclear magnetic resonance of 131I and 132I oriented in Fe

Nuclear magnetic resonance has been applied to radioactive I nuclei oriented in Fe. By field shifting the ¹³¹I resonance the hyperfine field is determined as positive. The ¹³¹I resonance at 683.3 ± 1.0 MHz and the ¹³²I resonance at 674.0 ± 0.5 MHz give H_int = 1144.0 ± 1.5 kOe.     

31P NMR in the ferromagnetic state of amorphous Fe75P15C10

The first observation of a metalloid site hyperfine field (hf) distribution in a ferromagnetic amorphous alloy is reported using a spin-echo NMR technique. The ³¹P nuclei in amorphous Fe₇₅P₁₅C₁₀ show a hf distribution with a maximum at about 27 kOe. The sample was prepared with Fe enriched to 99.93% in ⁵⁶Fe. A comparison of the NMR spectra on samples containing natural Fe and ⁵⁶Fe also provides the ⁵⁷Fe hf distribution whose peak value agrees with Mössbauer results.     

Low-temperature Mössbauer studies of FeNb2O6

Fe⁵⁷ Mössbauer spectra of FeNb₂O₆ were obtained from 15.0K down to 1.9 K. The isomer shift, 1.42±0.01 mm sec^?1 relative to Cr, was found to be temperature independent, whereas the magnitude of the quadrupole splitting was observed to decrease slightly with temperature. The quadrupole splitting and the hyperfine field at 1.9 K are -2.41±0.01 mm sec^?1 and 34.6±0.3 kOe respectively. The directions of the hyperfine fields experienced by the Fe nuclei are in the a-c plane symmetrically displaced with respect to the crystallographic axes.     

Magnetization process of Fe layers in Fe/Nd multilayered films investigated by57Fe Mössbauer spectroscopy

The magnetization process of Fe and Nd layers at 5K in Fe/Nd multilayered films with strong perpendicular magnetic anisotropy is elucidated from a comparison of⁵⁷Fe Mössbauer spectra in the presence of the external field applied parallel to the film plane with total magnetization. At zero external field, the film has a magnetic multi-domain structure. The Nd layer moment is perpendicular to the film plane and the Fe layer moment points in the out-of-plane direction. The Fe layer moment monotonically rotates to the in-plane direction with increasing external field parallel to the film plane, while the Nd layer moment is oriented to the film normal direction up to the external field of 10kOe, above which the Nd layer moment gradually turns to the direction of the external field.     

Mössbauer study of amorphous Nd−Fe−B films and their crystallization processes

Amorphous Nd?Fe?B films prepared by rf sputtering and their crystallization processes have been investigated by Mössbauer spectroscopy. A preferable alignment of the magnetization was observed in the amorphous film with a low hyperfine field of 173 kOe. With crystallization the average hyperfine field increases sharply, and the preferable alignment of the magnetization vanishes rapidly. The spectrum of the sample annealed at 750°C with coercivityH _c=15.7 kOe shows that only Nd₂Fe₁₄B phase exists.     

A Mössbauer effect study of the Sb impurity site hyperfine field in amorphous Fe80B20

Mössbauer effect was used to determine the Sb site hyperfine field in the amorphous ferromagnet Fe₇₉SbB₂₀. The¹²¹Sb Mössbauer spectrum at 77 K showed a distribution of hyperfine fields with a most probable value of 219 kOe. This result is discussed in terms of the systematics of non-magnetic site hyperfine fields in ferromagnets.⁵⁷Fe Mössbauer effect was also used to determine the most probable value of the Fe site field, , and the width of the field distribution, H. Our measurements yield 280 kOe and H=104 kOe. These results are consistent with previous results on the amorphous ferromagnet Fe₈₀B₂₀.     

Features of the hyperfine interaction of tin impurities in metallic holmium

The Mössbauer effect has been used to study the hyperfine fields for the¹¹⁹Sn atom as an impurity in metallic Ho in the 4.5–136 K temperature range. Two values of the field relevant to the features of the Ho magnetic structure have been found in the ferro- and antiferromagnetic regions of ordering. The temperature dependence of the fields differs drastically from the magnetization function and is similar to the case of a Dy host studied earlier. The experiments with a 40 kOe external magnetic field at 25 K have revealed a strong (up to 19%) hysteresis in the hyperfine fields which can be explained by a rearrangement of the magnetic structure. The field sign has been found to be negative, from which fact a peculiar compensation of the local and hyperfine fields is deduced. The experiment is also indicative of a possible new phase transition at 95 K.     

57Fe Mössbauer effect study of well-crystallized goethite (α-FeOOH)

Well-crystallized, natural goethite has been investigated as a function of temperature. The saturation magnetic hyperfine field was found to be 507 kOe and the Néel temperatureT _N=(400±2) K. The antiferromagnetic structure is stable in external fields of up to 6O kOe and the spin direction is at right angles with respect to the EFG's principal axis. AtT/T _N<0.5, the reduced hyperfine field varies asT ² and in the range 0.80<T/T _N<0.97 asT ^1/3. From the temperature dependence of the isomer shift, the Debije temperature was found to be 440 K from which a relative Mössbauer fraction of 0.96 against hematite was evaluated.     

Transferred hyperfine fields at 119Sn in Fe1−xMxSn [M≡Mn, Co and Ni]

The transferred hyperfine fields at ¹¹⁹Sn, using Mössbauer spectroscopy are reported for the hexagonal B-35 compounds with a general formula Fe_1?xM_xSn, where MMn, Co and Ni. In these compounds, Sn atoms occupy two crystallographically inequivalent sites. For FeSn the observed spectrum consists of a quadrupole doublet and a magnetic pattern corresponding to 2(d) and 2(a) sites respectively. The data have been analysed to resolve the controversy regarding hyperfine parameters. On replacing Fe by Mn atoms, additional lines appear in the higher velocity region of the Mössbauer spectrum and the intensity of the nuclear Zeeman pattern increases at the expense of quadrupole doublet. The resulting Mössbauer spectra have been analysed by taking only the nearest neighbour interactions into account. This analysis shows that on replacing each Fe atom by a Mn atom, the hyperfine field at 1(a) Sn site increases by about 40 kOe and a field of about 35 kOe is produced at the 2(d) Sn sites. Further, from the nuclear Zeeman pattern for 2(d) sites, the sign of quadropole splitting for these sites could also be determined and was found to be positive. However, the substitution of Co and Ni in place of Fe atoms results in a broad unresolved pattern suggesting that the hyperfine field at the 1(a) sites decreases and a finite field develops at the 2(d) site. The origin of transferred hyperfine fields at the two inequivalent Sn sites is discussed, the magnetic transition temperatures of these compounds have been estimated and the magnetic moments of M-atoms have been inferred.     

Theg-factor of the 181 keV level of99Tc and hyperfine fields of Tc in Fe,Co, Ni

Theg-factor of the 181 keV-level of⁹⁹Tc has been redetermined by the spin rotation method. Measurements with polycrystalline sources of Tc in Fe, Co, and Ni yielded values of the hyperfine fields at the Tc nucleus. $$\begin{gathered} g = + 1.310(25) \hfill \\ H_{hf} (Tc{\mathbf{ }}in{\mathbf{ }}Fe) = ( - )290(15)kOe \hfill \\ H_{hf} (Tc{\mathbf{ }}in{\mathbf{ }}Co) = ( - )170(5)kOe \hfill \\ H_{hf} (Tc{\mathbf{ }}in{\mathbf{ }}Ni) = - 47.8(1.5)kOe. \hfill \\ \end{gathered} $$