A 57Fe and 119Sn Mössbauer study of BaFe4Sn2O11

The Mössbauer spectrum of BaFe₄Sn₂O₁₁ has been recorded for both ⁵⁷Fe and ¹¹⁹Sn isotopes at a variety of temperatures. In the paramagnetic state the ⁵⁷Fe spectra are interpreted in terms of three iron environments. Magnetic ordering begins at 77 K and is virtually complete by 4.2 K to give an average magnetic hyperfine field of 504 kG. The ¹¹⁹Sn spectra also reflect the magnetic ordering and a magnetic hyperfine field of 45 kG is transferred to the tin nuclei.     

Zero-field and in-field Mössbauer spectroscopy as a tool for structural and magnetic characterization of maghemite (γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>) nanoparticles

Nowadays, nanoparticles of maghemite (γ-Fe₂O₃) represent one of the most useful materials in modern advanced nanotechnological applications due to their superior magnetic properties. For their characterization,⁵⁷Fe zero-field and in-field Mössbauer spectroscopy have proved themselves to be very powerful and effective tools which are crucial for an investigation of the local surrounding of iron atoms and observation of dynamic effects. The structural and magnetic characteristics of maghemite and its nanoparticles are thus discussed with regard to their zero-field and in-field Mössbauer spectra recorded at various temperatures and applied external magnetic fields. In addition, a special attention is also devoted to remarkable physical phenomena (superparamagnetism, spin canting) occurring largely in maghemite nanosized particles.     

57Fe and119Sn Mössbauer investigations on some substituted barium hexaferrites

⁵⁷Fe and¹¹⁹Sn Mössbauer measurements have been carried out on powder samples of three differently substituted M-type barium hexaferrites. By⁵⁷Fe Mössbauer measurements in an external magnetic field applied parallel to the -ray direction, we found a canted spin structure for all samples. Furthermore, we detected a strong preference of the Sn⁴⁺ ions for the 4f₂ sites. From⁵⁷Fe Mössbauer measurements aboveT _N, we conclude that the substitution does not influence the 2b sites. The analysis of the magnetically split¹¹⁹Sn Mössbauer spectra at room temperature in the case of the Co-Sn and Zn-Sn substituted samples shows a strong difference between the two. The spectra were interpreted due to the different surroundings of the Sn⁴⁺ ions.     

Local magnetic structure and anomalies of magnetic hyperfine interactions of57Fe and119Sn nuclei in lithium aluminium ferrites

The⁵⁷Fe and¹¹⁹Sn Mossbauer spectra of ordered ferrites Li_0.5Fe_2.5−xAl_xO₄∶Sn for 0.8<x<1.0 (the compensation point region) have been studied. The spin glass type magnetic structure with the spin canting angle depending on temperature and aluminium concentration is established. Anomalies in the temperature dependence of the hyperfine magnetic field at tin nuclei have been found near the compensation point of the ferrites     

Tin-doped spinel-related oxides of composition M3O4 (M = Mn, Fe, Co)

Tin-doped compounds of spinel-related M₃O₄ (M = Fe, Mn, Co) have been studied by ¹¹⁹Sn and ⁵⁷Fe Mössbauer spectroscopy in the temperature range of 20–600 K. The ¹¹⁹Sn Mössbauer spectra recorded down to 20 K from the non-iron-containing compounds of Co₃O₄ and Mn₃O₄ contained only doublets showing no transfer of magnetic properties from cobalt or manganese to the dopant tin ions. In contrast, the tin-doped-(FeCo)₃O₄ and (FeMn)₃O₄ gave ¹¹⁹Sn and ⁵⁷Fe Mössbauer spectra, which showed magnetic hyperfine interactions. The Curie temperature has been estimated for the former sample.     

Magnetic hyperfine fields of vacancy-associated119Sn in ion-implanted nickel

Magnetic hyperfine fields of¹¹⁹Sn impurity defects in nickel have been investigated by Mössbauer emission spectroscopy. Radioactive¹¹⁹Xe isotopes were implanted, annealing was performed after¹¹⁹Xe had decayed to¹¹⁹Sb. At least five different components with well-defined magnetic hyperfine fields, isomer shifts and Debye temperatures are identified in the rather complex spectra. One of these (B=2T) is known to be due to substitutional Sn. The hyperfine fields of the other components are pronouncedly larger (B=9T, B=15T, and B=17T, respectively, for single crystals). These defects are proposed to be Sn-multivacancy defects.     

A Mössbauer study of FeSn2 at 100 K in applied fields

⁵⁷Fe and¹¹⁹Sn Mössbauer spectra have been recorded at 100 K in applied fields of 32 and 64 kG on a FeSn₂ sample obtained by arranging single crystal needles side by side. The present work confirms that the Sn fields are anisotropic above T_t=93 K. The field model has been used to determine the magnetic structure of FeSn₂ below T_t.     

Crystallographically-based analysis of the NMR spectra of maghemite

All possible iron environments with respect to nearest neighbour vacancies in vacancy-ordered and vacancy-disordered maghemite have been evaluated and used as the foundation for a crystallographically-based analysis of the published NMR spectra of maghemite. The spectral components have been assigned to particular configurations and excellent agreement obtained in comparing predicted spectra with published spectra taken in applied magnetic fields. The broadness of the published NMR lines has been explained by calculations of the magnetic dipole fields at the various iron sites and consideration of the supertransferred hyperfine fields.     

Hyperfine interactions of tin atoms in samarium

The hyperfine interactions of ¹¹⁹Sn impurity atoms in samarium at temperatures from 5 to 70 K are investigated by Mössbauer spectroscopy. The distributions P of magnetic hyperfine fields B _hf for tin atoms at sites of the hexagonal [P _h(B _hf)] and cubic [P _c(B _hf)] samarium sublattices are determined from the experimental absorption spectra. Ion ordering in pairs of magnetic centers located in layers of the cubic sublattice is observed by Mössbauer spectroscopy for the first time. Each magnetic center involves ordered ions at the nearest neighbor sites of the tin atom replacing the samarium ion at the hexagonal lattice site. The quadrupole coupling constant e ² q _hQ=0.59±0.12 mm/s is determined for tin atoms at the hexagonal sublattice sites of samarium. The quadrupole interaction of tin atoms in heavy rare-earth metals (from Tb to Er) with a hexagonal close-packed structure is discussed.     

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.     

Study of hexagonal R-type BaFe4Sn2O11 by57Fe and119Sn Mössbauer spectroscopy

Mössbauer data have been obtained from both the⁵⁷Fe and¹¹⁹Sn isotopes for BaFe₄Sn₂O₁₁. Variable temperature studies show that magnetic ordering occurs at 77K and is probably complete at 4K. Average hyperfine fields of 504kG and 45kG were observed at the iron and tin nuclei respectively.     

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.     

Magnetism of ultrathin Cr layers and Fe/Cr multilayers studied by 119Sn probes

Cr/Sn and Fe/Cr/Sn/Cr multilayers, where monatomic Sn layers are embedded in Cr layers and Fe/Cr multilayers respectively, were prepared by means of ultrahigh-vacuum deposition technique, and the magnetic hyperfine field induced at the ¹¹⁹Sn nuclear sites was examined using conversion electron Mössbauer spectroscopy. The magnetic structures of the Cr layers are inferred from the size and direction of the magnetic hyperfine field transferred at the Sn sites.     

Magnetism of ErAgSn studied by 119Sn Mössbauer spectroscopy

Antiferromagnetic ErAgSn compound was investigated in detail by ¹¹⁹Sn Mössbauer spectroscopy in a temperature range between 2.2 and 300 K. The ¹¹⁹Sn spectra recorded below 4.2 K can be well fitted with a single main magnetic component in agreement with recent neutron diffraction studies [1]. A broad distribution of magnetic hyperfine fields observed above 4.2 K and enhanced spin correlations among Er³⁺ ions at T > T _N = 5.6 K are the remarkable features of the investigated system.     

Studies of119Sb ions adsorbed on ferrimagnetic spinel oxide CoFe2O4 surfaces by means of emission Mössbauer spectroscopy

The chemical states of¹¹⁹Sb⁵⁺ ions hydrolytically adsorbed on spinel type ferrimagnetic oxide CoFe₂O₄ powders are studied by means of emission Mössbauer spectroscopy of the daughter nuclide¹¹⁹Sn. The spectra show a broadening which is attributed to the supertransferred hyperfine magnetic field coming from the magnetically ordered metal ions of the substrate. Distribution of the field is obtained from the spectra and its change with temperature is discussed.     

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%.     

Preparation and characterisation of electrodeposited amorphous Sn-Co-Fe ternary alloys

Electrochemical deposition was investigated as a process to obtain alloys of Sn-Co-Fe, which to date have not been reported in the literature. A constant current technique was used to electrochemically deposit tin-cobalt-iron alloys from a gluconate electrolyte. The gluconate system was chosen as an electrolyte, which could potentially provide an environmentally safe process. The effect of plating parameters such as current density, deposition time, temperature and pH are discussed. Results are reported for current density and plating time using an electrolyte temperature of 20-60 °C and pH of 7.0 in relation to phase composition, crystal structure and magnetic anisotropy of the deposited alloys.Investigations were conducted using ⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS), ¹¹⁹Sn CEMS, transmission Mössbauer Spectroscopy and XRD. The ⁵⁷Fe and ¹¹⁹Sn CEMS spectra and XRD showed that the dominant phase in the deposits was amorphous Sn-Co-Fe. The relative area of the 2nd and 5th lines of the sextets representing the magnetic iron containing phases was found to decrease continuously with increasing current density while at the same time no significant changes in the magnetic anisotropy was found with plating time. Magnetically split ¹¹⁹Sn spectra reflecting a transferred hyperfine field were also observed.A range of good quality amorphous Sn-Co-Fe ternary alloys was obtained over a range of operating conditions from an environmentally acceptable gluconate electrolyte.     

Vacancy ordering in γ-Fe2O3 nanocrystals observed by Fe NMR

The identification by ⁵⁷Fe internal field nuclear magnetic resonance (NMR) of hyperfine fields at four Fe sites in the (average) tetragonal unit cell of vacancy-ordered γ-Fe₂O₃ (maghemite) is reported. The effects of vacancy redistribution due to annealing the partially vacancy-ordered form has been observed in the ⁵⁷Fe lineshape. In addition, the reduction of the particle size of the vacancy-ordered form has been observed to gradually eliminate the vacancy ordering and then to cause a transition from ferrimagnetism to superparamagnetism.     

Magnetic hyperfine fields acting on diamagnetic119Sn impurity in rare-earth-3d transition metal laves phases,crystallized under high pressure

A summary of the magnetic and the electronic properties of Laves Phases compounds RT₂ (R=Sm-Lu; T=Fe, Co, Ni) synthesized under high pressure is presented. The hyperfine fields acting on tin impurity nuclei in RT₂ have been obtained by Mössbauer spectroscopy. It has been found that hyperfine fields at¹¹⁹Sn and their temperature dependences for the RFe₂ (R=Sm-Ho), the RCo₂ (R=Sm-Tb) and GdNi₂ prepared at high and atmospheric pressures, are substantially different, respectively.     

Magnetic and Mössbauer studies of pure and Ti-doped YFeO 3 nanocrystalline particles prepared by mechanical milling and subsequent sintering

Single-phased nanocrystalline particles of pure and 10 % Ti ⁴⁺-doped perovskite-related YFeO ₃were prepared via mechanosynthesis at 450^°C. This temperature is ～150–350 ^°C lower than those at which the materials, in bulk form, are normally prepared. Rietveld refinements of the X-ray diffraction patterns reveal that the dopant Ti ⁴⁺ ions prefer interstitial octahedral sites in the orthorhombic crystal lattice rather than those originally occupied by the expelled Fe ³⁺ ions. Magnetic measurements show canted antiferromagnetism in both types of nanoparticles. Doping with Ti ⁴⁺ lowers the Néel temperature of the YFeO ₃ nanoparticles from ～ 586 K to ～ 521 K. The Ti ⁴⁺-doped YFeO ₃ nanoparticles exhibit enhanced magnetization and coercivity but less magnetic hyperfine fields relative to the un-doped nanoparticles. The ⁵⁷Fe Mössbauer spectra show ～ 15 % of the YFeO ₃ nanoparticles and ～22 of Ti ⁴⁺-doped YFeO ₃ ones to be superparamagnetic with blocking temperatures < 78 K. The broadened magnetic components in the ⁵⁷Fe Mössbauer spectra suggest size-dependent hyperfine magnetic fields at the ⁵⁷Fe nuclear sites and were associated with collective magnetic excitations. The ⁵⁷Fe Mössbauer spectra show the local environments of the Fe ³⁺ ions in the superparamagnetic nanoparticles to be more sensitive to the presence of the Ti ⁴⁺ ions relative to those in the larger magnetic nanoparticles.