Mössbauer spectroscopic study of FeAl1−x Co x

We report the results of a Mössbauer study of the alloy sytem FeAl_1?x Co _x forx ≥ 0.3 at temperatures down to 83 K. Magnetic splitting is observed forx ≥ 0.35 at all temperatures. However, forx=0.3, no splitting is observed at room temperature, and superparamagnetic behavior occurs at LN₂ temperature. The magnetically split spectra are fitted each with a distribution of hyperfine fields and the average hyperfine field \(\bar B_{hf} \) as a function of temperature is obtained. The variation of \(\bar B_{hf} \) withT is explained using the model of magnetic clusters with collective magnetic excitations from which the saturation hyperfine field and the magnetic anisotropy energy for these clusters are obtained. Also, the results are discussed using the model of random atomic distributions, and the agreement between the calculated and the experimentally obtained distributions of hyperfine fields is found improve asx increases.     

Mössbauer studies of GdFe2 − x Hf x alloys

GdFe_2???x Hf _x alloys, where x?=?0, 0.10, 0.15, 0.20, and 0.30, are produced by arc-melting of pure elements. The samples are investigated by x-ray diffraction and Fe⁵⁷ Mössbauer spectroscopy at 78 K and 300 K. We find that the alloy system GdFe_2???x Hf _x have the single phase cubic Cu₂Mg type structure in the whole concentration range. Mössbauer spectroscopic results show that all the samples studied are magnetically ordered at 78 K, and at room temperature. The room temperature spectra are fitted with two magnetic components where the direction of magnetization is along the [111] while the spectra at 78 K are fitted with four magnetic subspectra indicating a complex direction of magnetization for all samples under investigation. The average magnetic hyperfine field and the average isomer shift are found to decrease almost linearly with increasing the Hf concentration at 78 K and 300 K due to the replacement of Fe by nonmagnetic Hf.     

Mössbauer studies of Fe x Mn1 − x S single crystals

Single crystals of iron manganese sulfides Fe _x Mn_{1 ? x} S (0.25 ≤ x ≤ 0.29) are experimentally investigated using Mössbauer spectroscopy and x-ray diffraction. The Mössbauer spectra measured at 300 K exhibit a single broadened line characteristic of paramagnets. The isomer shift of this line is equal to 0.92–0.94 mm/s, which is typical of Fe²⁺ ions in the octahedral position. The quadrupole splitting (0.18–0.21 mm/s) suggests a distortion of the coordination polyhedron of iron ions in the Fe _x Mn_{1 ? x} S compounds.     

Magnetic properties and Mössbauer studies in Y1−x Gd x Fe2

Alloys of Y_1???x Gd _x Fe₂B _y (x = 0, 0.25, 0.5, 0.75 and 1; y = 0, 0.1, 0.15 and 0.2) have been prepared and investigated for structural and magnetic properties. The compounds with x = 0 and 1 are found to form in single phase with C15-type cubic Laves phase structure, while those with x = 0.25, 0.5 and 0.75 are observed to form with small quantities of secondary (Y,Gd)Fe₃ phase. The lattice parameters, Curie temperature and the average Fe hyperfine field are found to increase with increasing x. The Gd–Gd and Gd–Fe interactions are attributed to be the main reason for the enhancement of magnetic properties. Boron was found to stabilize the (Y,Gd)Fe₂ phase without affecting the magnetic properties.     

Tellurium-125 Mössbauer spectroscopy study of molybdenum metal tellurides of composition Mo6−x M x Te8 (M=Ru,Rh)

Tellurium-125 Mössbauer spectra have been recorded from some recently reported superconducting compounds Mo_6?x Ru _x Te₈ (x=0, 0.5, 1.0, 1.5) and Mo_5.5Rh_0.5Te₈. The spectra are characterised by single lines which probably contain contributions from the crystallographically dissimilar tellurium sites in these compounds. The trends in the linewidth and chemical isomer shift data are consistent with the enhanced polarisation of tellurium 5p electrons with increasing ruthenium content in the compounds. The results can be related to the nature of chemical bonding in the cluster of metal atoms.     

Mössbauer study of spin states in amorphous Fe100−x Zr x alloys

Spin states in amorphous Fe_100–x Zr_x (7x12) are investigated using hyperfine field distributions (HFDs) as derived from⁵⁷Fe transmission Mössbauer experiments. The existence of low-, medium- and high-spin states is demonstrated by three-dimensional projections of HFDs. Temperature dependences of the corresponding average values revealed anomalous behaviour in the vicinity ofT _fc. An increase in the hyperfine magnetic fields observed towards low temperatures is discussed in terms of a ferromagnet-to-spin-glass transition. Utilizing also theT _c values, which were obtained from a thermal scanning Mössbauer technique, we propose a diagram of spin states in amorphous Fe-Zr.     

Mössbauer and magnetization studies on the ferromagnet Fe3−x Ru x Si

⁹⁹Ru and⁵⁷Fe Mössbauer spectroscopic studies were carried out on ternary intermetallic compounds containing ruthenium, Fe_3–x Ru _x Si, within the concentration range 0.1x1.5. Magnetization of the samples was also measured in the temperature range between 4 K and room temperature.⁹⁹Ru Mössbauer spectra ofx=0.5 and 1.0 were fitted satisfactorily with a broad component ofH _hf, the peak positions of which were 340 and 270 kOe, respectively.     

Superionic conductivity of the heterovalent solid solutions R 1−x M x F 3−x (R=REE, M=Ca, Ba) with tysonite-type structure

The fluorine-ion conductivity of anion-deficient solid solutions R _1−x Ca_xF_3−x and R _1−x Ba_xF_3−x having the tysonite (LaF₃) structure was investigated by the impedance spectroscopy method. R _1−x Ca_xF_3−x (R=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho) and R _1−x Ba_xF_3−x (R=La, Pr, Nd) single crystals were grown from the melt by the Bridgman-Stockbarger method. The electrophysical measurements were performed in the frequency range 5−5×10⁵ and temperature range 300–700 K. The temperature dependences of the electrical conductivity for the crystals studied is determined by the migration of fluorine anions along various structural positions. It is shown that, from the standpoint of increasing the conductivity of tysonite matrices RF₃ (R=La, Pr, Nd), doping by CaF₂ and BaF₂ is less promising than SrF₂. Fiz. Tverd. Tela (St. Petersburg) 41, 638–640 (April 1999)     

Mössbauer studies on Tb x Fe1−x alloy films with perpendicular magnetic anisotropy

Amorphous ferrimagnetic Tb _x Fe_1?x films with perpendicular magnetic anisotropy and Tb _x Fe_1?x /NiFe exchange-coupled structures characterized by unidirectional anisotropy are obtained. The magnetic and chemical inhomogeneity of alloys of Tb _x Fe_1?x compensation composition is established on the basis of Mössbauer studies of these systems.     

Mössbauer study of amorphous (Fe1−x Ga x )84B16

Using the⁵⁷Fe Mössbauer effect the influence of the Ga content in amorphous (Fe_1?x Ga _x )₈₄B₁₆ on the average hyperfine fields \(\bar H\) and isomer shift has been studied. For the sample (Fe_0.98Ga_0.02)₈₄B₁₆ the \(\bar H\) , as well as the recoilless fraction,f _a were measured as functions of temperature ranging from 12 K to 300 K. The experimental results show a linear correlation between Inf _a and δ, and well as between δ andx. In the temperature range \(\bar H(T)\) can be described by the Brillouin function and the second-order Doppler shift is appreciable. The characteristic temperature for such an amorphous alloy is 372 K. the effective vibrating massM _eff=79 a.u.     

Mössbauer study of Y2Fe17N x (x < 3) nitrides

⁵⁷Fe Mössbauer spectra of Y₂Fe₁₇N_x nitrides were measured. The hyperfine field (H _hf) and the average isomer shift for Y₂Fe₁₇ increase obviously after nitrogenation. Forx1.1, however, the averageH _hf varies only slightly, while the increase ofH _hfat each iron site is somewhat different and more pronounced at 4f dumbbell sites than at the other sites when the nitrogen concentration is increased. This means that the influence of the nitrogen atoms on the local magnetic properties of the iron atoms depends sensitively on the configuration of the nearest-neighbor atoms around the iron atoms. The results are compared with the⁸⁹Y NMR spectra of Y₂Fe₁₇N _x .This project was supported by the National Natural Science Foundation and the State Key Magnetism Laboratory of China.     

Critical behaviour of Ho 2 Fe 17 − x Mn x —magnetisation and Mössbauer spectroscopy

The magnetic properties of Ho₂Fe_17???xMn_x compounds (x = 0–2) of ferromagnetic ordering temperatures up to T_C ~344 K have been investigated by DC magnetization and Mössbauer effect measurements. The nature of the magnetic phase transitions and the critical behaviour around T_C has been investigated by analysis of the magnetisation data and the critical exponents β, γ and δ determined. The critical exponents are found to be similar to the theoretical values of the mean-field model for which β?=?0.5 and γ?=?1.0, indicating the existence of a long-range ferromagnetic interactions. The isothermal entropy changes ΔS around T_C have been determined as a function of temperature in different magnetic fields.     

237Np Mössbauer Investigations of (U1−x Np x )2Rh2Sn

Surprisingly, Np₂Rh₂Sn does not order magnetically whereas the uranium counterpart U₂Rh₂Sn orders antiferromagnetically at 24 K with a 5f moment μ _U ≈0.38μ _B . We have investigated the magnetic and electronic properties of (U_1−x Np _x )₂Rh₂Sn solid solutions. For x=0.25 and 0.5, the ordering temperature decreases to 11 K whereas the Np-rich compound (x=0.75) shows the onset of magnetic order around T≈6 K. The average Np magnetic moment amounts to 0.84 μ _B ,0.83μ _B and 0.25 μ _B respectively. The isomer shift slightly decreases, from −9.6 mm/s to −10.4 mm/s (versus NpAl₂) as x increases. The values of the quadrupole interaction parameter in the ordered and paramagnetic state suggest that Np moments are parallel to c for x=0.25 and then rotate to the basal plane for higher x. This revised version was published online in September 2006 with corrections to the Cover Date.     

Structural and 57Fe M?ssbauer study of EuCr1???x Fe x O3 nanocrystalline particles

Emission (⁵⁷Co) M?ssbauer spectra of the aspartic acid—⁵⁷CoCl₂ system were measured at T?=?80?K in frozen aqueous solution and in the form of a dried residue of this solution. The M?ssbauer spectra, besides a weak contribution from after-effects, showed two Fe^2?+?/Co^2?+? components which were ascribed to octahedrally and tetrahedrally coordinated ⁵⁷Co^II microenvironments in the Asp–cobalt(II) complex. This dual coordination mode may be due to the involvement of the second terminal carboxylic group of aspartic acid in the coordination sphere of Co.     

A Mössbauer effect study of the Fe2+x Mn1–x Al Heusler alloys

In this work the Mössbauer spectroscopy has been used to study the magnetic properties of Fe_2?+?x Mn_1???x Al alloys with small deviations of composition from the stoichiometric 2:1:1. The Mössbauer parameters obtained for the L2₁ phase indicate H _hf fields of about 25 T and 30 T at 80 K for Fe atoms at X sites in the ordered X₂YZ structure of the L2₁ full Heusler alloys.     

Magnetic and Mössbauer studies on nanocrystalline Co1−x Li x Fe2O4 (x = 0, 0.2)

Ultrafine particles of Co_1???x Li _x Fe₂O₄ (x?= 0, 0.2) samples are prepared by glycine–nitrate combustion route. X-ray diffraction and transmission electron microscopy studies show that the samples have cubic spinel structure and average crystallite sizes of x?= 0 and 0.2 are 36 and 44 nm respectively. Vibrating sample magnetometer studies revealed the ferromagnetic nature of the samples. Li-doped CoFe₂O₄ sample showed higher values of coercive field, remanent magnetization and saturation magnetization compared to pure CoF₂O₄ indicating the enhancement of magnetic interactions. Mössbauer spectra at 77 K exhibited two broad sextets indicating that Fe^3?+? ions occupy both tetrahedral and octahedral sites. From these studies, it is concluded that Co_1???x Li _x Fe₂O₄ (x?= 0, 0.2) samples exhibit an inverse spinel structure. At room temperature, two sextets are superimposed on a very broad non-Lorentzian background indicating the presence of superparamgnetic fraction in agreement with the microscopic observations.     

Mössbauer effect study of the pseudo-binary system (Ti1−x Nb x )Fe2

Mössbauer spectroscopy and X-ray diffraction measurements have been done on (Ti_1–x Nb _x )Fe₂ compounds in order to investigate the effect of Nb on the magnetic properties of TiFe₂. The experimental results show that Nb enters the lattice by filling Ti sites, thereby forming a continuous phase over the whole range of Nb concentrations. The Mössbauer spectra at 80 K fitted with a magnetic hyperfine field distribution show a continuous decrease of the average magnetic hyperfine field with increasing Nb concentration, as well as several different magnetic configurations forx0.3.     

Mössbauer study on Zn1 − x Fe x O semiconductors prepared by high energy ball milling

We present the preparation of massive Zn_1???x Fe _x O ternary oxides using the mechanical mill. The Fe atom is a particular dopant since it presents two different oxidation states which allow us to vary the starting materials: Fe₂O₃, $\upalpha $ -Fe or FeO. Parameters such as initial concentrations, atmosphere and milling times were varied. X-ray diffraction and ⁵⁷Fe Mössbauer spectrometry (MS) were applied in order to analyze the structure evolution and iron incorporation in the wurtzite crystalline structure with milling time. At final stages, Fe atoms seem to be incorporated in the ZnO structure for those samples milled under Ar atmosphere. In all cases, two paramagnetic components, attributed to Fe atoms in both valence states, were observed by MS.     

121Sb Mössbauer spectroscopy of Mn1+x Sb

¹²¹Sb Mössbauer spectra for ferromagnets, Mn_1+x Sb (0.00≤x≤0.22) in ε phase were measured at 77 K. The large unique hyperfine magnetic field (H _hf=361 kOc) atx=0 tends to decrease and to have a wide distribution with increase ofx. The decreasing ratio of the mean value ofH _hf for the nonstoichiometric samples is in accordance with that of their magnetizationM _S(x), i.c., the relation \(\overline {H_{hf} } (x)/H_{hf} (0) = M_S (x)/M_S (0)\) holds in this system.     

Mössbauer study of mixed valent silicides Eu(Ir1−x Pd x )2Si2

The solid solutions Eu(Ir_1–x Pd _x )₂Si₂, which exist for 0x0.125 and 0.75x1. cristallize with the tetragonal ThCr₂Si₂-type structure. The variation of the europium valence with composition has been thoroughly studied at temperatures 4.2T293 K by¹⁵¹Eu Mössbauer resonance. For 0x0.125 the europium valence at room temperature decreases asx increases. For 0.75x1 the valence transition temperature Eu³⁺Eu²⁺ increases asx increases.