Temperature anomaly of the Cd hyperfine field in a trivacancy complex in Ni

The temperature dependence of the Cd hyperfine field in a trivacancy complex in Ni between 25 and300 K is reported. It was found that, unlike the Cd substitutional field in Ni which follows the temperature dependence of the magnetization, the Cd hyperfine field in a trivacancy complex is essentially temperature independent. This temperature anomaly is compared with other temperature anomaly of impurity hyperfine fields in ferromagnetic hosts.     

Temperature dependence of the iron hyperfine field distribution in amorphous Fe-rich Fe-Zr alloys

The temperature dependence of the iron hyperfine field distribution is reported in melt-quenched amorphous Fe-Zr alloys. The most remarkable feature is the compositinal change in the shape of the average hyperfine field versus temperature curves. The unusual increase in the average hyperfine field below about 85 K is a characteristic feature of the RSG systems; however, no anomaly is observed in the width of the hyperfine field distribution as a function of temperature. The results cannot be properly explained in the framework of the existing spin glass models.     

Temperature dependence of the magnetic hyperfine splitting of metastable iron-amalgam

The temperature dependence of the magnetic hyperfine field of a metastable iron-mercury alloy has been measured. The Mössbauer spectrum obtained at 12 K can be fitted with two magnetically split components with hyperfine fields of 39.7 and 36.0 T. With increasing temperature the hyperfine fields decrease much more rapidly than that of α-Fe. The temperature dependence is in accordance with the Bloch law up to 220 K.     

Temperature-independent hyperfine field on μ+ in nickel in the temperature range of 0.12–300 K

The hyperfine field on a positive muon at interstitial site in a nickel single crystal has been measured by the muon spin rotation method in the temperature range from 0.12 K to 300 K. The hyperfine field in the low temperature limit was found to be ?640.7±2.2 Gauss. While the saturation magnetization decreases by 7% as the temperature increases from 0.1 K to 300 K, the hyperfine field seen by the muon remains nearly constant. Possible mechanisms for explaining this result are considered.     

Hyperfine Fields of 181Ta in UFe4Al8

The γ–γ Perturbed Angular Correlation technique was used to study the hyperfine interaction of ¹⁸¹Ta at the Hf site(s) in UFe₄Al₈ at room temperature and 12 K. The data at room temperature are well described by two electric field gradients, while at low temperature two combined hyperfine interactions have to be considered, one with the magnetic hyperfine field collinear with the c-axis and another with the magnetic hyperfine field in the basal plane. The results are compared with previous Mössbauer and neutron diffraction experiments and the lattice site of Hf is discussed.

     

Search for spin canting in gadolinium iron garnet using the Mössbauer technique

We have studied the hyperfine interactions in GdIG in zero external magnetic field using⁵⁷Fe Mössbauer spectroscopy. Measurements were made at temperatures between 80 K and 310 K, whereby the region around the compensation point at 286 K was emphasized. The easy axis of magnetization was determined to be [111] at all the chosen temperatures. No indications of spin canting were found. The hyperfine parameters vary smoothly with temperature. The temperature dependences of the magnetization of the sublattices are deduced from the magnetic hyperfine fields.     

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.     

The spin density waves in chromium detected by hyperfine field measurements

The magnetic hyperfine field of tantalum nuclei in a high purity chromium matrix has been measured using the Time Differential Perturbed Angular Correlation technique. The spectra show that the hyperfine field is proportional to the amplitude of the spin density wave of chromium and that the tantalum probe nuclei do not clamp the phase of the spin density wave. The incommensurate antiferromagnetic first order phase transition as well as the spin flip transition have been observed. The temperature dependence of the hyperfine field is shown to deviate from the temperature dependence of the maximum magnetization of the spin density wave.     

The temperature dependence of the magnetic hyperfine field of tantalum in dysprosium

The temperature dependence of the magnetic and electric hyperfine interactions at the site of ¹⁸¹Ta impurities in polycrystalline Dy has been measured between 4.2 and 178 K using the time differential perturbed angular correlation technique. The value of the magnetic hyperfine field at 4.2 K is: |H_hf(TaDy)| = 212(9) kG The temperature dependence of the magnetic hyperfine field follows closely the prediction of the molecular field model.     

Hyperfine interaction of 181Ta in nickel

Nuclear gamma resonance spectroscopy was used to study the hyperfine interaction of ¹⁸¹Ta impurities in nickel at room temperature and above the Curie point. Both the hyperfine field for ¹⁸¹Ta in nickel at room temperature and the isomer shift relative to Ta metal have been derived.     

Resolved magnetic hyperfine spectra of Au-Fe alloys as a function of temperature

We have analyzed the Mössbauer hyperfine magnetic spectra of six compositions of Au-Fe from 10.5 to 33 at.% Fe at temperatures ranging from 4.2 K to the magnetic ordering temperature of each alloy. Only two elementary magnetic hyperfine spectra are required to fit the data, each of which has its own value of the magnetic hyperfine field, quadrupole coupling, isomer shift, and relative intensities. The intensity ratios of the two spectra for a given Fe concentration are essentially invariant with temperature. These results point to the existence of two chemically different Fe sites with all the Fe atoms magnetically coupled over the entire temperature regime below the upper magnetic ordering temperature. A relatively sharp increase in the local moment commences at both Fe sites, at ∼ 17 at.% Fe and continues to increase with Fe concentration.     

Nuclear resonant time spectra for Sn in Co2TiSn Heusler alloy films

Co₂TiSn Heusler alloy films were grown on MgO substrates at the substrate temperature between 200 and 600 °C using atomically controlled alternate deposition and magnetic hyperfine field at the Sn nuclei was measured by the Mössbauer spectroscopy and the nuclear resonant scattering method. The relation between the hyperfine field and the structural disorder estimated by X-ray diffraction measurements was also examined. The results showed that the sample prepared at higher substrate temperature has higher degree of L2₁ order and larger hyperfine field. For the Co₂TiSn film grown at 600 °C, the hyperfine field estimated from the oscillatory pattern of the nuclear resonant time spectra was 6.1 T at room temperature and increased with a decrease of temperature to 7.5, 8.1, and 8.3 T at 200, 100, and 5 K, respectively, which shows that the film prepared by this method and condition has almost the same magnetization value and Curie temperature as bulk samples.     

Mössbauer spectra of superparamagnetic Fe3O4

The Mössbauer effect is used to study the superparamagnetic behaviour of ultrafine Fe₃O₄ particles as a function of temperature and applied magnetic field. In zero field the disappearance of the hyperfine splitting with increasing temperature is observed. With the application of an external field the hyperfine spectrum is redeveloped.     

Hyperfine field of positive muon in ferromagnetic nickel

The electronic structure around a positive muon μ⁺ at an octahedral interstitial site of a ferromagnetic nickel is calculated from first principles. The hyperfine field experienced by μ⁺ at absolute zero is calculated to be ?0.72 kG in satisfactory agreement with the experimental value of ?0.64 kG. The calculation also explains the temperature dependence of the hyperfine field. It is shown that the temperature dependence of the hyperfine field coupling constant A(T) is predominantly determined by single particle excitations.     

Hyperfine magnetic fields in Fe−Co alloys and their tempera ture dependences

We obtained⁵⁷Fe hyperfine field parameters from Fe₁−x-Co _x alloys (0≤x≤0.6) from 77 K to 900 K. We first discuss the origin of the low temperature hyperfine fields in terms of the 3d and 4s electrons at⁵⁷Fe atoms. The⁵⁷Fe hyperfine magnetic field (hmf) of Fe-Co alloys depends more weakly on temperature than the hmf of pure Fe. This temperature dependence occurs because the alignment of the magnetic moments at both the Fe atoms and at the Co atoms depend on temperature in the same way as the bulk magnetization of Fe-Co alloys.     

The hyperfine interaction of As in Gd metal

The temperature dependence of the internal magnetic hyperfine field at As in Gd metal has been measured by IPAC technique at 90, 140, 193, 230 and 300 K. The reduced hyperfine magnetic field shows slight deviation from the Brillouin function for J=7/2.     

Mössbauer study of very dilute Pd(Fe) alloys at very low temperatures

The magnetic behaviour of very dilute (7 ppm and 0.6 ppm) Pd(Fe) alloys has been studied by Mössbauer spectroscopy in external fields up to 6 T in the temperature range between 0.018 and 300 K. No magnetic ordering was observed even at the lowest temperature. Above 0.067 K the magnetization exhibits free-spin behaviour. The saturation moment was found to be independent of temperature. Magnetic hyperfine patterns observed below 0.067 K were interpreted in terms of paramagnetic hyperfine interactions in the regime of slow electronic relaxation.     

Mössbauer studies of hyperfine fields in disordered Fe2CrAl

Heusler-like alloy Fe₂CrAl was prepared and studied. Structure determination was done by X-ray. The structure was found to conform to the B₂ type. Magnetic hyperfine fields in this sample were studied by the Mössbauer effect. The Mössbauer spectra were recorded over a range of temperature from 40 to 296 K. The Mössbauer spectra showed the co-existence of a paramagnetic part with a magnetic hyperfine portion at all recorded temperatures. Even with the distribution in the magnetic hyperfine field, the average hyperfine field follows the (T/T _c)^3/2 law. The paramagnetic part of the hyperfine field is explained in terms of the clustering of Cr atoms.     

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.     

Effect of atomic environment on the Fe hyperfine structure and the thermal stability of magnetic order in L10 ordered Fe-Pt alloys

The ⁵⁷Fe Mössbauer effect measurements were made for the L1₀ ordered Fe-Pt alloys with 39-62 at% Pt and the effect of local atomic environment on the hyperfine structure was investigated. Furthermore, the thermal stability of magnetic order was investigated for the alloys with high Pt concentration. From the analyses of the observed Mössbauer spectra, we found that dipole-field-like anisotropic transferred hyperfine fields are mainly responsible for the large difference in hyperfine field between Fe-site and Pt-site in the Fe-rich alloys. In the Pt-rich region far from stoichiometry, the existence of many Fe-sites occupied by excess Pt atoms causes a distribution of exchange fields. Therefore, the iron atoms in different local environments may have their several hyperfine fields with different temperature dependence. The anomalous temperature dependence of the averaged hyperfine field and line broadening observed for the 61, 62 at% Pt alloys can be understood from the co-existence of various sub-spectra with different temperature dependence. As a result, the thermal stability of magnetic order is largely reduced as the Pt concentration exceeds 60 at%.