Test for the influence of relaxation on Mössbauer spectra of (Fe0.65Ni0.35 1−x Mn x alloys by the sharpening method

A mathematical procedure which gives an opportunity to distinguish between relaxation and static mechanisms of the Mössbauer line broadening is developed. It is based on the method of Mössbauer line sharpening developed recently and allows one to answer unambiguously the question whether or not relaxation manifests itself in Mössbauer measurements by examinign the wings of the spectrum. The procedure was applied to the spectra of (Fe_0.65Ni_0.35)_1–x Mn _x alloys withx=0 (INVAR) andx=0.047, where the mechanism of the line broadening has not been clarified so far. An analysis of the spectra shows that in the temperature range 4 to 300 K no relaxation is observed and the line broadening is mainly caused by the distributions of magnetic hyperfine fields.     

Superconductivity and magnetism in Y1−x Ca x Sr2GaCu2O7−δ

Samples of Y_1–x Ca _x Sr₂GaCu₂O_7– (x=0, 0.4) doped with⁵⁷Fe, prepared under various oxygen pressures, have been studied by magnetometry and Mössbauer spectroscopy. Most of the iron ions (Fe³⁺) enter the Ga(Cu(1)) site. For thex=0 sample, the Mössbauer spectra of the iron nuclei in the Cu(2) sublattice display magnetic order of Cu,T _N=370 K. The iron ions in the Ga site display magnetic order only at low temperatures. At temperatures above 90 K, these iron ions display a pure quadrupole doublet Mössbauer spectrum. The samplex=0.4 also displays magnetic order of the Cu(2) site,T _N370 K. A sharp drop in the hyperfine field is observed atT _N, probably associated with a first-order phase transition or two-dimensional ordering. The iron nuclei in the Ga site display paramagnetic long spin relaxation time phenomena at 4.2 K. Thex=0.4 sample prepared under 110 atm oxygen pressure, displays superconductivity,T _c50 K. The Mössbauer spectra give evidence of the presence of two phases. One displays magnetic order, the other is paramagnetic, the last is probably associated with the superconducting phase.     

Characterization of a soil ilmenite developed from basalt

A natural ilmenite was extracted from the silt fraction of a soil developed from basalt of Minas Gerais State, Brazil. The sample was characterized by chemical analysis, X-ray diffraction, magnetic measurements and Mössbauer spectroscopy. The Mössbauer spectrum at 293 K shows two doublets: a major subspectrum of Fe²⁺ (relative area 74%) and a minor one of Fe³⁺ (26%). An incipient magnetic structure appears at 85 K, with a broadline sextet. These results may be explained by supposing that the separate is a solid solutionxFeTiO₃ · (1–x)Fe₂O₃, withx=0.85, which is magnetically ordered at low temperature. The lattice parameters for this hexagonal structure area=0.5082±0.0001 nm andc=1.398±0.001 nm.On leave of absence from the Departamento de Química, Universidade Federal de ViÇosa, 36570 000 ViÇosa (MG), Brazil.     

Magnetic order in Sr x Ca1−x Cu0.99 57Fe0.01O2

Sr _x Ca_1–x Cu_0.99 ⁵⁷Fe_0.01O₂ was studied forx=0.13, 0.15, and 0.17. Mössbauer spectroscopy and magnetization measurements indicate magnetic ordering characteristic of spin glass systems withT _f70K forx=0.15 and 0.13.     

Magnetic ordering in Fe-doped Gd2BaCuO5

The structural and magnetic properties of iron-doped Gd₂BaCuO₅ have been studied by X-ray diffractometry, Mössbauer spectroscopy and susceptibility measurements. Mössbauer data on Gd₂BaCu_0.8Fe_0.2O₅ show that at room temperature Fe is not magnetically ordered, displaying hyperfine parameters similar to those generally assigned to Fe at Cu(2) sites in the GdBa₂(Cu_1–x Fe _x )₃O₇ superconductor. Susceptibility measurements demonstrate that Gd₂BaCu_1–x Fe _x O₅ behaves like a three-dimensional antiferromagnet withT _N=11.9±0.1 K, independent ofx. The effective magnetic moment calculated within a mean field approximation is consistent with an ordering of the Gd sublattice.     

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.     

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.     

Fe57 Mössbauer study in cobalt substituted magnetite

The Mössbauer effect has been studied in the mixed ferrites Co _x Fe_3–x O₄ (forx=0.8, 0.9 and 1) with the spinel structure in the temperature range between 78 and 380 K. The composition withx=1, showed an expected Zeeman spectrum with two overlapping magnetic hyperfine patterns related to the Fe³⁺ ions in tetrahedral and octahedral sites. While for samples withx=0.8 and 0.9 the Mössbauer spectrum for each compound was successfully analysed into three different patterns corresponding to the ferric ions placed at the tetrahedral and octahedral sites and ferrous ions at the octahedral sites, indicating no electron transfer between Fe³⁺ and Fe²⁺, where the quantity of cobalt is sufficiently large to be located at the six nearest neighbours to ferrous ions. The Mössbauer effect parameters were calculated for these observed sites and their variation with temperature reported. The reduced hyperfine magnetic fields of the Fe³⁺ (B) ions were found to follow the Brillouin curve forS=5/2 and one third power law. The magnetic ordering temperature was determined to be 815 K and the possible magnetic interactions were discussed.     

Magnetic Relaxation in Nano-Phase Chromium Substituted Goethite

The magnetic and crystalline properties of chromium substituted goethite, -Fe_(1–x)Cr_(x)OOH (where x=0.00, 1.44, 3.00, 7.00, 10.14 wt.%) were studied using Mössbauer spectroscopy and X-ray diffraction. Transmission electron microscopy measurements showed that as the chromium concentration increased from 0 to 10.14 wt.%, the particle size decreased rapidly from 200 to 10 nm. X-ray diffraction analysis indicated that no lattice strain was present, even for chromium concentrations as high as 10.14 wt.%. Mössbauer spectra recorded at 300 K showed the presence of superparamagnetic relaxation in each sample. The relative area of the doublet component decreased, while that of the sextet component increased as the temperature decreased from 300 to 77 K. The mean hyperfine field measured at 77 K decreased from 49.6 T for the pure goethite to 44.9 T for the 10.14 wt.% chromium substitution. This decrease in the hyperfine field was attributed to both decreasing particle size and increasing chromium concentration.     

Correlation between site preference and magnetic properties of substituted strontium ferrite thin films

SrFe_12−x(Sn_0.5Zn_0.5)_xO₁₉ thin films with x=0−5 were synthesized by a sol-gel method on thermally oxidized silicon wafer (Si/SiO₂). The site preference and magnetic properties of Zn-Sn substituted strontium ferrite thin films were studied using ⁵⁷Fe Mössbauer spectroscopy and magnetic measurements. Mössbauer spectra displayed that the Zn-Sn ions preferentially occupy the 2b and 4f₂ sites. The preference for these sites is responsible for the anomalous increase in the magnetization at high Zn-Sn substitutions. X-ray diffraction (XRD) patterns and field emission scanning electron microscope (FE-SEM) micrographs demonstrated that single phase c-axis hexagonal ferrite films with rather narrow grain size distribution were obtained. Vibrating sample magnetometer (VSM) was employed to probe magnetic properties of samples. The maximum saturation of magnetization and coercivity at perpendicular direction were 265 emu/g and 6.3 kOe, respectively. It was found that the complex susceptibility has linear variation with static magnetic field.     

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.     

Magnetic Structure of FexCu100−x Magnetoresistive Alloys Produced by Mechanical Alloying

Fe _x Cu_100–x magnetoresistive alloys were produced by mechanical alloying. X-ray diffraction shows fcc structure. The room-temperature Mössbauer spectra evolves from an asymmetrical doublet below x=25%, to a broad magnetic hyperfine field distribution above this concentration. Quadrupole splitting of the doublet varies between 0.48 and 0.57 mm/s, and its isomer shift from 0.16 to 0.29 mm/s. Low-temperature Mössbauer spectroscopy displays a B _hf distribution. Magnetization measurements display different features depending on concentration, from mictomagnetism to ferromagnetism. Low-temperature magnetoresistance is measured. Samples with x20% exhibit larger magnetoresistivity ratios. Bulk and hyperfine magnetic properties are correlated in order to explain magnetoresistivity features of these samples.     

Mössbauer and magnetic investigation of Fe-Mn alloy

Mössbauer, X-ray, magnetization and susceptibility measurements were performed to study Fe_100–x Mn _x ,x=5, 15, 39, 50. The different phases of Fe-Mn were identified, and hyperfine interaction parameters and average magnetic moments of some samples were determined. The average hyperfine field and average magnetic moment decrease asx increases. The influence of the Mn neighbourhood on the derived parameters is discussed in the light of calculations using the first principle discrete variational method in the local density approximation.     

Magnetic and structural features of amorphous FeMo-based alloys

NANOPERM-type FeMoCuB alloys are studied using magnetic and Mössbauer measurements in the as-prepared amorphous state. It is shown that the Fe₇₆Mo₈Cu₁B₁₅ (A) and Fe₇₄Mo₈Cu₁B₁₇ (B) alloys exhibit the magnetic dipole and electrical quadrupole interactions well detected in the room-temperature Mössbauer spectra. The thermomagnetic measurements above the room temperature indicate a vanishing of the magnetic interactions at approximately 310 K (A) and at 340 K (B), respectively. The low-temperature DC magnetic measurements show an anomaly around 200 K which is also a boundary at which zero-field Mössbauer measurements of both samples reflect the gradual “vanishing” of the electrical quadrupole interactions and appearance of another magnetically ordered component. The Mössbauer measurements in the field of 4 MA/m yield a survival of quadrupole and an enhancement of magnetic dipole interactions.     

Cluster glass-like behavior of the diluted antiferromagnet Fe x Mg1−x TiO3 (x=0.2,x=0.3)

A diluted antiferromagnet Fe _x Mg_1–x TiO₃ has been shown to behave as a spin glass (x=0.2) and a reentrant spin glass (x=0.3) near the Fe percolation concentrationx 0.25. In order to obtain microscopic information on these samples, we performed Mössbauer measurements. At considerably higher temperatures than the transition temperatures, magnetically broadened spectra appear superimposed upon the paramagnetic doublets. A remarkable feature is that the intensity of the magnetic spectra increases accompanying the decrease of their linewidth. This behavior can be ascribed to the gradual slow-down of fluctuations of the antiferromagnetic clusters formed at high temperatures. To investigate the temperature variations of the relaxation time of the clusters, we analyzed the Mössbauer spectra using the method formulated by Blume. It has been shown that becomes long with decreasing temperature and the rate of the slow-down of is hastened aroundT _SG andT _N.     

Eu and Fe Mössbauer study of mechanically alloyed EuFeO3

EuFeO₃ was prepared by mechanical alloying starting from europium and iron oxides. After 20 h of milling the resulting compound is pure EuFeO₃. Samples were studied as a function of milling period using XRD, Mössbauer, SEM, and magnetic measurements. Mössbauer spectroscopy was used to probe both the transition metal and the rare-earth sites. Results are compared with previous works on EuFeO₃ prepared by different methods.     

Mössbauer,X-ray diffraction and AC susceptibility studies on nanoparticles of zinc substituted magnesium ferrite

Nanoparticles of zinc substituted Mg-ferrite with compositions Mg_(1-x)Zn _x Fe₂O₄ (x = 0.15, 0.30 and 0.50) having particle sizes in the range 6.4 nm to 21.4 nm prepared by the co-precipitation method were characterized by ⁵⁷Fe Mössbauer spectroscopy, X-ray diffratometry and AC magnetic susceptibility measurements. Mössbauer measurements at room temperature and down to 20 K clearly indicate presence of superparamagnetic particles in all the samples. AC magnetic susceptibility data show lowering of blocking temperature with decrease of particle size. Superparamagnetic relaxation was observed for larger particle size in samples with higher Zn content, which is attributed to the weakening of A-B exchange interaction in ferrite lattice due to replacement of Fe^{3 +} in tetrahedral site by Zn^{2 +} ions.Received: 16 April 2004, Published online: 23 July 2004PACS: 75.50.Tt Fine-particle systems; nanocrystalline materials - 76.80. + y Mössbauer effect; other gamma-ray spectroscopy - 75.30.Cr Saturation moments and magnetic susceptibilitiesS. Das: Present address: Department of Physics, Jadavpur University, Kolkata - 700032, India     

EFG determination in magnetic field oriented powders of YBa2(Cu1−x 57Fe x )3O7−y superconductors: A test of existing models

YBa₂(Cu_1-x ⁵⁷Fe _x )₃O_7–y powder samples withx=0.02 and 0.03 were uniaxiallyc-aligned in epoxy in a magnetic field of 7.5 T. An X-ray map of the distribution of the orientation of the crystallographicc-axes of the individual crystallites was determined.⁵⁷Fe Mössbauer spectra were recorded at room temperature as a function of the angle between the texture axis and the observation direction. Different sets of EFG parameters were selected from the literature and the fit constraints were equally set for all. Using a model of the measured texture function and accounting for polarization-dependent blackness effects, a simultaneous fit of the Mössbauer spectra results in minimum ² for the EFG set determined previously from CEMS data on this films.On leave from: Institute for Low Temperature Physics and Engineering, Ukr. Acad. Sci., Kharkov, Ukraine.     

Mössbauer and magnetic studies of orthorhombic FeSiO3

Magnetic properties of orthoferrosilite FeSiO₃ have been examined using susceptibility, magnetization measurements and Mössbauer spectroscopy. From magnetic and Mössbauer measurements, one obtains close values of the magnetic ordering temperature, T_N=39±1 K and T_N=41±1 K, respectively. The magnetic order is characterized by strong ferromagnetic coupling of Fe²⁺ moments within the ribbons and a weak antiferromagnetic coupling of the moments between adjacent ribbons. The 4.2 K Mössbauer spectra can be fitted with two different hyperfine magnetic fields H_hf=68 kOe and H_hf=314 kOe which can be assigned to Fe²⁺ in the octahedrally coordinated M1 and M2 sites, respectively, of the FeSiO₃ structure.