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 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.     

X-ray, Mössbauer, and dielectric studies of the Co1 − x Ni x Cr2O4 ceramic system

The temperature dependences of the dielectric constant, ?(T), dielectric loss tangent, tanδ(T), and thermostimulated depolarization currents of (Co_{1 ? x} Ni _x )Cr₂O₄:y ⁵⁷Fe₂O₃ samples with 0.2 ≤ x ≤ 0.6 and 0.01 ≤ y ≤ 0.04 exhibit anomalies at temperatures of T ₁ ≈ 220 K and T ₂ ≈ 240 K that indicate a transition to an ordered ferroelectric state at temperatures below T ₂. Also observed at the same temperatures are abrupt changes in the isomer shift and quadrupole splitting for two Mössbauer spectral doublets of a sample with x = 0.2.     

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.     

Magnetic and Mössbauer spectral studies of x (NiFe2O4) + (1−x)(SrFe12O19), x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0 nanocomposites

Nano size composite of x(NiFe₂O₄)+(1?x)(SrFe₁₂O₁₉) were prepared using sol gel and aerosol route. The percentage of the components of NiFe₂O₄ and SrFe₁₂O₁₉ calculated from X-ray diffraction pattern using Rietveld analysis. The hysteresis loop for the as obtained samples exhibits no hysteresis, which may be attributed to super paramagnetic relaxation. The saturation magnetization do not show a significant change with the increase of strontium ferrites, however, the coercivity increased from 115 to 6,000 Oe. The Mössbauer spectra of these nano composites were discussed along with the magnetic moment and X-ray results.     

Magnetic and Mössbauer study of Mg0.9Mn0.1Cr x Fe2−x O4 ferrites

The ferrites Mg_0.9Mn_0.1Cr _x Fe_2?x O₄ ( The ferrites Mg_0.9Mn_0.1Cr _x Fe_2−x O₄ () were prepared using the conventional double sintering method. The XRD showed that the samples maintain a single spinel cubic phase. The M?ssbauer measurements were carried out at room and liquid nitrogen temperatures. From the area ratios of the A and B sites, it was found that the Fe cation population of the A and B sites decreases in proportion to Cr concentration. The contact hyperfine fields at the A and B sites were found to decrease with increasing Cr contents. This was found to be in approximate agreement with the results of magnetization measurement. The distributions of Mg and Mn cations versus Cr concentration were also determined using the M?ssbauer and magnetization results. The Curie temperatures were determined and found to agree with the reported values. As the Cr contents increases the relative magnetization, was found to increase at low temperatures and decreases at higher temperatures.     

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.     

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 X-ray studies for Ni0.2ZnxMg0.8−xFe2O4 ferrites

The spinel ferrites of Ni_0.2Zn_xMg_0.8−xFe₂O₄, 0⩽x⩾0.8, were studied at room temperature using X-ray diffraction and Mössbauer patterns. The analysis of the X-ray diffraction patterns proved that the samples have a single phase cubic spinel structure. The calculated values of the theoretical, true and average lattice constants, tetrahedral bond, tetrahedral edge and unshared octahedral edge were found to increase while the shared octahedral edge and octahedral bond decrease as the Zn²⁺ ion substitution increases. Mössbauer studies showed that the samples for x=0, 0.2 and 0.4 are magnetic and show rather broad lines, while for x=0.6 and 0.8 are paramagnetic. The hyperfine parameters of the tetrahedral and octahedral sites were determined as functions of composition x. The cation distributions were deduced and supported by X-ray studies. The B-site pattern was composite and has been fitted into multicomponents and the deduced hyperfine parameters have been discussed as a function of x.     

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.     

57Fe Mössbauer study of Li x Fe1-y Co y PO4 (y = 0, 0.1, 0.2) as cathode material for Li-ion batteries

Lithium iron phosphates LiFe_1-y Co _y PO₄ (y = 0, 0.1, 0.2) exposed to a charging process were studied by ⁵⁷Fe Mössbauer spectroscopy taking into account XRD and SEM data. Hyperfine parameters of the spectra were determined above and below the magnetic ordering temperature for all the samples. It was shown that the presence of Co impurity atoms in lithium phosphates gives no effect on the hyperfine interaction of ⁵⁷Fe²⁺ cations. However, Co atoms in the nearest cation environment of Fe atoms lead to a significant change of the hyperfine interactions of ⁵⁷Fe³⁺ cations. The Co impurity atoms distribution over the positions of the iron atoms in the structure is found not to be statistical,but correlated.     

Mössbauer studies of the charge transfer process in the system (Li0.5Fe0.5)1−xFexFe2O4

Conclusion The formation of heterovalent pairs seems to be proved for the compounds rich in Fe²⁺ ions (x0.5) and the electron-phonon coupling seems to change with decreasing concentration of Fe²⁺ ions.Nevertheless the pairs model is not necessarily an unique interpretation of the data for x0.5 /1/ and the broadening of the Fe^m+ ions spectrum could be worked considering electronic and atomic disorders.     

M?ssbauer and magnetic studies of Mn0.1Sr0.2Co0.7Fe2O4 nanoferrite

The magnetic properties of Mn_0.1Sr_0.2Co_0.7Fe₂O₄ nanoferrite with particle size of about 8 nm were investigated using magnetization and Mössbauer spectroscopy measurements. The sample shows a large increase in coercive field from 0.045 kOe at room temperature to about 3.00 kOe at 4 K. Room temperature coercive fields increased with increase in the annealing temperature between 300°C and 800°C. Our results show evidence of transformation from single domain to multi-domain structure with thermal annealing.     

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.     

Mössbauer and magnetic studies on nanocrystalline NiFe2O4 particles prepared by ethylene glycol route

NiFe₂O₄ nanoparticles have been synthesized by co-precipitation method at 145°C in N₂ atmosphere using ethylene glycol as solvent and capping agent. This gives the promising synthesis route for nanoparticles at low temperature. The as-synthesized NiFe₂O₄ is subsequently heated at 400°C, 500°C, 700°C and 800°C. Crystallite size increases with the heat treatment temperature. The heat treatment temperature has direct effect on the electron paramagnetic resonance and intrinsic magnetic properties. The room temperature Mössbauer spectrum of the 800°C heated sample shows the two sextets pattern indicating that the sample is ferrimagnetic and Fe^3?+? ions occupy both tetrahedral and octahedral sites of spinel structure.     

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.     

Magnetic and119Sn Mössbauer studies on a new Heusler alloy Co2ScSn

A new alloy, having the formula, Co₂ScSn, has been prepared. This is found to have the cubic Heusler L2₁ type structure (a = 6.19A). Magnetization measurements reveal a large drop in magnetization around 270K. Low field ac susceptibility also shows a transition at 268K which we take to be the Curie temperature of the alloy. The magnetic moment at 5K is found to be 0.55 _B per cobalt atom.¹¹⁹Sn Mössbauer measurements at 8K show a hyperfine split spectrum with a hyperfine field of about 40 kOe. Attempts to prepare other Co₂RSn alloys particularly with R=Lu, were not successful.     

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 and positron annihilation studies in plastically deformed Fe72−xAl28Tix (x=0, 2, 9) alloys

Positron lifetime measurements in deformed Fe–Al–Ti alloys, obtained by filing the homogenized ingots show that monovacancies are created during the filing process. This is in contrast with known results on deformation due to rolling where dislocations have been reported as the major defect type. These results together with those from Mössbauer spectroscopy suggest that the vacancies are dominantly created due to aluminum atoms being displaced to the nearby sites where they replace iron atoms. Annealing at 900°C for extended periods caused defect concentration to greatly reduce. Positron lifetime spectroscopy has been successfully used to detect agglomeration of vacancies to form di- or tri-vacancies for the first time. Addition of titanium is found to facilitate fast removal of defects during controlled heat treatments.