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.     

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.     

Growth-induced perpendicular magnetic anisotropy and clustering in NixPt1−x alloys

Polycrystalline and epitaxial (1 0 0), (1 1 0), and (1 1 1)-oriented Ni₃Pt, NiPt, and NiPt₃ films were deposited over a range of growth temperatures from 80°C to 700°C. Films grown at moderate temperatures (200–400°C) exhibit growth-induced properties similar to Co–Pt alloys: enhanced and broadened Curie temperature, perpendicular magnetic anisotropy and large coercivity. As in Co–Pt, the magnetic properties suggest a clustering of Ni into platelets on the growth surface, as the films are being grown. Unlike Co–Pt, however, NiPt films exhibit a strong orientational dependence of anisotropy and enhanced Curie temperature, possibly resulting from different types of surface reconstructions which affect the growth surface.     

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.     

57Fe Mössbauer and infrared studies of the system Co1−x Cd x Fe2O4

Mössbauer and infrared studies were made on samples of the ferrite system Co_1–xCd_xFe₂O₄ x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1. Mössbauer spectra were taken at room temperature. The spectra of the samples withx0.7 showed well defined Zeeman patterns and they have been analyzed with two components, one due to A-site Fe³⁺ ions, and the other due to B-site Fe³⁺ and Fe²⁺ ions. The pattern due to B-site appeared to be composite and an explanation is given. The spectra withx=0.9 and 1 showed only a quadrupole splitting. The effect of cadmium substitution on the various hyperfine interactions has been discussed and the cationic distribution has been deduced for all values ofx. Far infrared spectra of the ferrite samples in the range 200–700 cm^–1 were reported. Four bands were observed: the high frequency bandv ₁ is assigned to tetrahedral complexes, and the low frequency bandv ₂ to octahedral complexes, a small bandv ₃ is due to Co²⁺-O^2– complexes andv ₄ is assigned to the lattice vibration of the system. The splitting occurred in thev ₁ andv ₂ bands atx=0.9 and inv ₂ atx=1, indicating the presence of Fe²⁺ ions in octahedral sites.     

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 studies of Fe–C combinatorially sputtered thin films

Alloys of Fe_{1? x} C _x were produced using combinatorial sputtering methods. The composition of the films as a function of position was determined using electron microprobe techniques and the results have shown that a composition range of about 0.35?<?x?<?0.75 was obtained. X-ray diffraction methods were employed to study the structure of the thin films and showed that all portions of the films were amorphous or nanostructured. Room temperature ⁵⁷Fe Mössbauer spectroscopy was utilized to study the atomic environment around the Fe atoms. Hyperfine field distributions of ferromagnetic alloys, as extracted from the Mössbauer analysis, suggested the existence of two classes of Fe sites: (1) classes of Fe sites that have primarily Fe neighbours corresponding to a high-field component in the distribution and (2) classes of Fe sites that have a greater number of C neighbours, corresponding to a low-field component. The magnetic splitting decreased as a function of increasing carbon concentration and alloys with x greater than about 0.68 were primarily paramagnetic in nature. These spectra exhibited distributions of quadrupole splitting with mean splitting in excess of 1.0?mm/s. This indicates a higher degree of local asymmetry around the Fe sites than typically seen in other Fe-metalloid systems.     

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 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.     

An X-ray diffraction and Mössbauer spectroscopic study on thec-axis texture YBa2(Cu1−x Fe x )3O7−y thick films

YBa₂(Cu_1–x Fe _x )₃O_7–y thick films (x=0, 0.01, 0.02, 0.03) on ceramic substrate were prepared. X-ray diffraction determinations show the formation of partialc-axis texture perpendicular to the surface of the ceramic substrate in the preparation process. The⁵⁷Fe Mössbauer spectra were measured at 300 K, where the angle between the incidence-ray beam and the surface of the film is 90° and 36°, respectively. The⁵⁷Fe Mössbauer spectra with=90° possess four sets of asymmetrical doublets.     

Hyperfine magnetic interactions in Tb(Fe1 − x Al x )2 alloys

The structural and magnetic characteristics of phase transformations in Tb(Fe_{1 ? x} Al _x )₂ alloys with concentrations x = 0?0.9 have been measured in the temperature range from 90 to 450 K. The temperature dependences of the hyperfine magnetic fields for each of local configurations of the nearest environment of iron atoms upon substitution of aluminum atoms for iron atoms have been found using Mössbauer spectroscopy.     

Mössbauer and PAC studies of nanocrystalline Fe

High-purity Fe powder was mechanically milled under argon at ambient temperature using an SPEX 8000 mill. The local atomic and magnetic structure was studied using⁵⁷Co/Fe Mössbauer and¹¹¹In/Cd perturbed angular correlations (PAC) spectroscopies. After 32 hours of milling, X-ray diffraction revealed effective grain diameters of 18 nm and energy-dispersive X-ray analysis indicated a Cr impurity concentration of 5%, presumably introduced by mechanical attrition of steel ball bearings used for milling. In addition to a spectral component very similar to bulk iron metal, the Mössbauer spectra exhibited hyperfine field shifts attributed to the Cr impurities. PAC spectra on Fe milled for 5 h, with no contamination, exhibited two components: (1) A slightly broadened magnetic interaction attributed to interior, defect-free sites of In/Cd probes with a mean hyperfine field slightly greater than in macroscopic grains. The defect-free site fraction grew appreciably during milling, even though In is essentially insoluble in Fe. (2) An indistinct signal due to mixed magnetic and quadrupole interactions attributed to probes at surface or other defect sites.     

155Gd Mössbauer investigation on (GdxNd1−x)1+εFe4B4

Tetragonal (Gd_xNd_1–x)₁₊ Fe₄B₄ alloys have been investigated for 0.2x1 by Mössbauer spectroscopy, using the 86.5 keV¹⁵⁵Gd resonance. The Gd quadrupolar interaction e²qQ=12.67(5) mm/s for x=1, nearly independent of x, is the largest observed to date in metallic compounds of Gd. A crystal field term A ₂ ⁰ =–2450±50 K/a ₀ ² is inferred. This quadrupolar interaction shows some dispersion increasing when x decreases, reflecting the quasi incommensurate nature of the (Gd,Nd) and Fe+B sublattices in the (Gd_xNd_1–x)Fe₄B₄ structure (=0.109 for x=0 and =0.139 for x=1). The hyperfine field is perpendicular to the c axis for x0, but no unique direction is obtained for x=0.     

A Structural,Magnetic and Mössbauer Study of Tb0.3Dy0.7(Fe1−x Al x )1.95 Alloys

A structural, magnetic and Mössbauer study of a series of Tb_0.3Dy_0.7(Fe_1–x Al _x )_1.95 alloys (x=0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature is presented. It was found that the primary phase of the Tb_0.3Dy_0.7(Fe_1–x Al _x )_1.95 alloys is the MgCu₂-type cubic Laves phase structure when x<0.3 and a small amount of a second phase, RFe₃ (R: rare-earth element), is present when 0.3x0.35. The lattice constant of the Tb_0.3Dy_0.7(Fe_1–x Al _x )_1.95 alloys increases approximately monotonically with increasing x. The substitution of Al increases slightly the magnetostriction in a low magnetic field (H500 Oe). However, the magnetostriction decreases sharply, but is saturated more easily with increasing x in a higher applied field. The analysis of the Mössbauer spectra allows the determination of the easy axes of magnetization in these alloys. Moreover, the dependence of the hyperfine-field, isomer shift and quadrupole splitting on the Al concentration, x, for the Tb_0.3Dy_0.7(Fe_1–x Al _x )_1.95 alloys are reported and discussed.     

Hyperfine fields and magnetic anisotropy in Fe1000−x Gd x thin films and Fe80−x GdxB20(0≤x≤24) thin films and ribbons

The Mössbauer measurements performed on Fe_100–x Gd _x thin films and on Fe_80–x Gd _x B₂₀ both as thin films and ribbons show a dependence of the spins orientation and H_hyp versus temperature, Gd content and preparation conditions. Increasing the Gd content, the initial low anisotropy disappears and H_hyp decreases. A sharp increase of the anisotopy with temperature in ribbons with low Gd concentration is evidenced.     

Mössbauer Study of La1−x Ca x Mn1−y 57Fe y O3 with x=0,0.25; y=0.01

Temperature dependent Mössbauer measurements are done on the samples of La_1–x Ca _x Mn_1–y ⁵⁷Fe _y O₃ with x=0 and 0.25, and y=0.01. With decreasing temperature, the specimen with x=0.25 shows a paramagnetic to ferromagnetic transition around 175 K. In the specimen x=0.0, the temperature dependence of both the center shift () and the recoilless fraction (f) can be fitted very well with the Debye theory with a _D=320±50 K. But for the specimens with x=0.25, f and show distinct deviations from the Debye behavior in the temperature range in which the resistivity shows a sharp decrease. Dips observed in both the f and around the transition temperature suggest that the Jahn–Teller distortion observed in these systems is dynamic in nature.     

Structural and Mössbauer spectroscopic studies of Fe0.7−xCrxAl0.3 alloys

Fe_0.7−xCr_xAl_0.3 alloys with x=0, 0.1, 0.2, 0.3 and 0.35 have been synthesized by arc melting and studied by X-ray diffraction and Mössbauer spectroscopy. All the samples studied were found to have single phase with body center cubic structure. The lattice parameter a, and hence the volume, were obtained from the X-ray diffraction patern and found to increase with increasing the chromium concentration. At room temperature Mössbauer studies show magnetic ordering for small values of x and paramagnetic behavior for large values of x under investigation. The Mössbauer spectra were analyzed considering a distribution of magnetic hyperfine fields for small values of x and two singlets were added for large values of x. During the fitting procedure, the relation between the hyperfine field and the isomer shift in the hyperfine field distribution was linear relation. The average hyperfine field and isomer shift as a function of chromium content x were found to decrease with increasing x. The results are explained in terms of local environmental effects on the hyperfine interactions.     

Structural origin of perpendicular magnetic anisotropy in Ni–W thin films

The magnetic properties and microstructure of electrodeposited Ni–W thin films (0–11.7 at% W in composition) were studied. The film structures were divided into three regions: an FCC nanocrystalline phase (0–2 at% W), a transition region from FCC nanocrystalline to amorphous phase (2–7 at% W), and an amorphous phase (>7 at% W). In the transition region, (4–5 at% W) films with perpendicular magnetic anisotropy (PMA) were found. The saturation magnetization, magnetic anisotropy field, perpendicular magnetic anisotropy and perpendicular coercivity for a typical Ni–W film (4.5 at% W) were 420 kA/m, 451 kA/m, 230 kJ/m and 113 kA/m, respectively. The microstructure of Ni–W films with PMA is composed of isolated columnar crystalline grains (27–36 nm) with the FCC phase surrounded by the Ni–W amorphous phase. The appearance of the interface between the magnetic core of Ni crystalline grains and the Ni–W non-magnetic boundary layer seems to be the driving mechanism for the appearance of PMA. The origin of PMA in Ni–W films is mainly attributed to the magnetoelastic anisotropy associated with in-plane internal stress and positive magnetostriction. The secondary source of PMA is believed to be the magnetocrystalline anisotropy of 〈1 1 1〉 columnar grains and its shape magnetic anisotropy. It is concluded that Ni–W electrodeposited films (4–5 at% W) may be applicable for perpendicular magnetic recording media.     

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.