CEMS interface study of Fe(100)/Pd film structures

The magnetic hyperfine fieldsB _hf near the interface in epitaxial Fe(100)/Pd thin film structures were analyzed using in-situ⁵⁷Fe conversion electron Mössbauer spectroscopy.B _hf is enhanced by about 12% in the 2nd Fe monolayer and approaches the Fe bulk value after a few oscillations within 8–10 Fe monolayers. This oscillating behavior can be described by a superposition of an exponential short-range and an RKKY-like long-range exchange interaction.     

The interaction of Fe on MgO(1 0 0) surfaces

The atomic interaction and magnetic properties of ultrathin Fe films grown on cleaved and polished MgO(1 0 0) surfaces were studied by conversion electron Mössbauer spectroscopy (CEMS). ⁵⁷Fe layers were deposited as probe atoms in different layer positions in 10 ML thick Fe films. Fe layers of different thicknesses were formed on polished and cleaved substrate surfaces at RT deposition. The analysis of the spectra showed no Fe-O^2- interaction in MgO/Fe interface. FeO phase formation was excluded. The Mössbauer spectrum of 5 ML ⁵⁷Fe sample showed enhanced internal magnetic field at 80 K. No interdiffusion of ⁵⁷Fe and ⁵⁶Fe atoms was observed between the layers at room temperature.     

Mössbauer spectroscopy investigation of body centered cubic Co in Co/Fe superlattices prepared with MBE

A new spectrum component is observed in Mössbauer spectra of thin body centered cubic Co layers prepared in Fe/Co superlattices doped with⁵⁷Co. It is characterized by a large magnetic hyperfine field (31.2 T) and an isomer shift nearly equal to that of -Fe. The decrease of the isomer shift in bcc Co with respect to hcp Co is consistent with smaller s to d charge transfer in bcc Co as compared to hcp Co. The cubic structure of the CoFe superlattices is evidenced with X-ray diffraction and ion-channeling measurements. The Fe/Co interface is investigated with conversion electron Mössbauer spectroscopy. It is shown that the interface alloy thickness is about six monolayers for growth temperatures up to 450 K and that increasing alloying occurs for higher growth temperatures.     

The effect of radiofrequency modulation of 57Fe hyperfine interaction by rotating magnetic field

The effect of ⁵⁷Fe hyperfine interaction radiofrequency (rf) modulation by external rotating magnetic field was studied in thin Permalloy foil by means of Mössbauer spectroscopy. The rf effect was investigated as a function of intensity for several rf field frequencies. The experiments show that the external rotating rf field causes considerable changes in the hyperfine pattern. The obtained spectra are in disagreement with those obtained by Perlow [Phys. Rev. 172 (1968) 319]. They also are inconsistent with magnetostriction hypothesis. Proceeding from the Mössbauer spectrum analysis one may conclude that the magnetization of investigated foil changes its direction in a complex manner. However, the undertaken experiments show that the essential number of Mössbauer nuclei experience the rotating magnetic field influence.     

Glass forming tendency in the FeBSn system

The glass forming tendency in the Fe-B-Sn system is studied. Samples were prepared by melt quenching and analyzed by X-ray diffraction. The glasses obtained were also analyzed by⁵⁷ Fe Mössbauer spectroscopy. Mössbauer spectra were fitted using hyperfine field distributions.     

High field Mössbauer investigations of FexN (x=3,4)

⁵⁷Fe transmission Mössbauer measurements were carried out on Fe₃N and Fe₄N in applied fields up to 13.5 T to study the influence of an external field (B _a) on the hyperfine field of Fe atoms with localized and itinerant moments. These results are compared with augmented spherical wave band structure calculations.     

Correlation of57Fe hyperfine interactions with Fe-Fe distance in Laves phase compounds RFe2 (R=rare earth)

The⁵⁷Fe Mössbauer isomer shifts and magnetic hyperfine fields in Laves phase compounds RFe₂ (R=Pr, Nd and Sm) are studied with particular reference to the effect of the Fe–Fe interatomic distance on the hyperfine interactions. It is shown that the charge density at the Fe nuclei scales linearly with fractional volume change up to 20%. The⁵⁷Fe hyperfine field corrected for the influence of rare-earth moment shows a systematic variation with the distance, which can be understood in terms of the Bethe-Slater curve arguments. The similarity of the atomic volume dependence of the⁵⁷Fe hyperfine interactions in Lves phase compounds to those in iron with close-packed structure is emphasized.This paper is based on a paper presented at the 5th Int. Conf. on hyperfine interactions, Berlin, July 21–25, 1980.     

The early iron age of the Mössbauer era

The demonstration that the 14.4 keV level of⁵⁷Fe was an ideal Mössbauer example produced a veritable explosion in the discoveries of new physical phenomena. Among the important features of⁵⁷Fe are its ready availability and ease of preparation, its magnetic properties in many environments, the high intensity of its Mössbauer spectrum even at elevated temperatures, the relative sharpness of the Mössbauer lines, and the possibility of obtaining the resolution provided by this sharpness by relatively simple techniques. This paper hopes to capture some of the excitement and enthusiasm generated by the discoveries and demonstrations of the nuclear Zeeman effect, together with its polarization properties, the nuclear isomer shift, the quadrupole splitting, the temperature effect, temporal effects, nuclear hyperfine fields, transferred magnetism, the gravitational red shift, and many other new or newly elucidated phenomena.     

A Mössbauer study on the surface hyperfine field of uniform hematite particles

A Mössbauer spectroscopic study was performed on uniform spherical hematite particles (99±9 nm, Sample I) and those enriched with⁵⁷Fe on the surface (Sample II). A striking difference was found between the spectra of these two samples, in that Sample I showed a spectrum with nearly symmetrical resonant absorption lines, while Sample II showed a spectrum with the lines broadened toward the central peaks asymmetrically. But after the⁵⁷Fe-enriched sample was heated to 623 K, the spectral lines became narrower due to the diffusion of the surface⁵⁷Fe-ions into the bulk. The above results showed that the centripetal broadening of the spectral lines for small uniform hematite particles resulted from a surface effect. The surface exhibited a hyperfine field about 5.2% lower than that for the bulk. The wider distribution of the surface hyperfine field was explained by structural inhomogeneity of the surface.     

57Fe Mössbauer studies of U(Fe1−x Co x )2

In the pseudo-binary alloy system U(Fe_1–x Co_x)₂, the ordering transition temperature and the magnetic moment decrease rapidly with x.⁵⁷Fe Mössbauer measurements on the alloys (x=0.08 and 0.20) have been performed as a function of temperature. The observed hyperfine field at the⁵⁷Fe nucleus is much reduced with respect to that in UFe₂.     

Magnetic coupling in Gd(Fe6−x Cr x )Al6: A57Fe Mössbauer study

⁵⁷Fe Mössbauer measurements have been made on the ternary ThMn₁₂-type intermetallic compounds Gd(Fe_6–x Cr _x )Al₆ withx=0, 0.5, 1.0, 1.5 and 2.0, at temperatures of 4.2 and 77 K. The principal effect of the Cr substitution is to reduce the⁵⁷Fe magnetic hyperfine field at 4.2 K in this series. The analysis of the⁵⁷Fe Mössbauer spectra is consistent with a ferromagnetic coupling between the Gd and Cr magnetic moments. These results are in agreement with previous studies by Felner et al. on GdCr₆Al₆, in which a ferromagnetic ordering withT _C=170 K was observed.On leave from Applied Acoustics Institute, Shaanxi Teachers University, Xian, PR China.     

Hyperfine interactions in metal extracted from ordinary chondrite Tsarev L5: A study using Mössbauer spectroscopy with high-velocity resolution

For the first time, a study of hyperfine interactions in metal grains extracted from ordinary chondrite Tsarev L5 was done using Mössbauer spectroscopy with high-velocity resolution. Three magnetic (sextets) and one paramagnetic (singlet) components were revealed in the Mössbauer spectrum of extracted metal. The evaluated values of the magnetic hyperfine field were 332.5, 335.4 and 347.2 kOe. On the basis of Mössbauer parameters and metallographic data, the magnetic components were related to the α-Fe(Ni, Co), α′-Fe(Ni, Co) and α₂-Fe(Ni, Co) phases of Fe(Ni, Co) alloy, while the paramagnetic singlet was related to the γ-Fe(Ni, Co) phase.     

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%.     

A Mössbauer effect study of Y(57Fe:Mn)12

The intermetallic compound, YMn₁₂, doped with 0.5at.%⁵⁷Fe has been investigated using the⁵⁷Fe Mössbauer resonance. The data show that the Fe impurities occupy preferentially the f-site at the expense of the i- and j-sites. Whereas the i- and j-sites are expected to carry identical local magnetic moments in the ordered state, low temperature hyperfine fields of 50.08(±0.05)T and 2.90(±0.03)T are measured for the i- and j-sites respectively. It is proposed that large transferred hyperfine fields are responsible for this disparity.     

Mössbauer studies of Dy2Fe17−yAly hydrides

The x-ray and Mössbauer measurements of both⁵⁷Fe and¹⁶¹Dy in Dy₂Fe_17–y Al (y=0, 1,5 and 3) compounds and their hydrides are reported.Hydrogenation slightly increases the lattice parameters. An appreciable increase of the isomer shift and the hyperfine field at⁵⁷Fe nuclei is observed after hydrogenation. The hyperfine field for both the parent compound and its hydride decreases with increasing Al content across the series. Only a small variation of the hyperfine field at¹⁶¹Dy nuclei is noticeable after hydrogenation.     

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.     

Effects of nitrogen and vanadium on the57Fe hyperfine field of RFe12−x V x N y (R=Y,Nd)

Magnetization and⁵⁷Fe Mössbauer measurements were carried out on RFe_12–x V _x N _y compounds (R=Y and Nd,x=1.7 and 2.2) and the effects of nitrogen and vanadium atoms on the⁵⁷Fe hyperfine fields at the different iron crystallographic sites were investigated. The hyperfine field decreases with increasing number of vanadium neighbour atoms at all the iron sites. The hyperfine field is strongly enhanced in the nitrogen composition withy>1 where the compound tends to transform into an amorphous-like solid. The iron moment deduced from the hyperfine field increases more upon nitrogenation for the 8i-site than for the other sites, and exceeds the moment of bcc iron.     

Local magnetic order in57Fe doped Y(Ce)Co4B

In order to monitor the peculiar temperature dependence of the magnetization of the compounds YCo₄B and CeCo₄B from an atomistic point of view, samples doped with 1%⁵⁷Fe were studied by Mössbauer spectroscopy. From the two Co-sites present in this structure (2c, 6i), only the latter were found to be equipped by Fe. In the case of the Y-compound, the change of direction of the easy axis of magnetization could be confirmed. The broad maximum observed for the magnetization of the Ce-compound is not reflected by the⁵⁷Fe hyperfine field.     

In-beam implantation of iron into germanium in an external magnetic field studied by the Mössbauer effect

In order to determine whether the doublet observed in the Mössbauer spectra of⁵⁷Fe after in-beam, recoil implantation into Ge is due to a quadrupole interaction or corresponds to two implantation sites, this implantation experiment was performed in the presence of a 35 kG external magnetic field. The resulting Mössbauer spectrum favors a dominant quadrupole interaction hypothesis.     

Mössbauer effect studies of the Dy12Fe82B6 system

The Mössbauer measurements of both⁵⁷Fe and¹⁶¹Dy in Dy₁₂Fe₈₂B₆ system are reported. The presence of B exceeds the magnetic hyperfine fields at both⁵⁷Fe and¹⁶¹Dy nuclei as compared to corresponding pure metals Fe and Dy respectively. The only small excess of the hyperfine field at⁵⁷Fe nucleus is observed. The excess at¹⁶¹Dy nucleus is about 12% of the free ion Dy³⁺ value.