g-Factors of magnetic–rotational states in 85Zr

The properties of the double iron and tungsten carbide prepared by mechanical alloying technique (MA) from elemental powders are reported. The samples were milled for 1, 3, 5, 10, 15, 20, 25 and 30 h. The alloy progress for each milling time was evaluated by X-ray diffraction (XRD) and ⁵⁷Fe Mössbauer spectrometry. Once the alloy was consolidated two sorts of paramagnetic sites and a magnetic distribution were detected according to the Mössbauer fitting. The majority doublet could correspond to Fe₆W₆C ternary carbide as X-ray diffraction suggests, and the other could be Fe₃W₃C. The hyper fine parameters are reported. Vickers microhardness measurements of 30 h milled sample was conducted at room temperature with a load of 0.245 N for 20 s.     

Mössbauer studies of hyperfine fields in disordered Fe2CrAl

Heusler-like alloy Fe₂CrAl was prepared and studied. Structure determination was done by X-ray. The structure was found to conform to the B₂ type. Magnetic hyperfine fields in this sample were studied by the Mössbauer effect. The Mössbauer spectra were recorded over a range of temperature from 40 to 296 K. The Mössbauer spectra showed the co-existence of a paramagnetic part with a magnetic hyperfine portion at all recorded temperatures. Even with the distribution in the magnetic hyperfine field, the average hyperfine field follows the (T/T _c)^3/2 law. The paramagnetic part of the hyperfine field is explained in terms of the clustering of Cr atoms.     

Kinetics of cementite mechanosynthesis

The influence of ball to powder ratio and discontinous milling during ball milling of Fe_0.75C_0.25 elemental powder mixture is presented. The formation of Fe₃C cementite, Hägg and ε carbides has been follwed by X-ray diffraction and Mössbauer Spectroscopy. Higher ball to powder ratios induce faster kinetics. Synthesized cementite has crystallite sizes 9 to 11 nm.     

Effect of FeCl3 and acetone on the structure of Na–montmorillonite studied by Mössbauer and XRD measurements

⁵⁷Fe Mössbauer spectroscopy, X-ray diffraction, X-ray fluorescence spectroscopy and infrared spectroscopy were used to study the effect of FeCl₃ and acetone on the structure of a Na–bentonite. XRD indicated the incorporation of Fe³⁺ ions into the interlayer space since the basal lattice spacing of montmorillonite increased to 1.6 from 1.24 nm after treatment with FeCl₃ dissolved in acetone. Interlayer Na⁺ ions could be exchanged to Fe³⁺. Magnetically split Mössbauer subspectra with internal magnetic fields 41 and 46 T at 74 K, were associated with two main Fe³⁺ microenvironments within the interlayer regions. The resultant Fe–montmorillonite was successfully applied as a catalyst in the preparation of 1,1-diacetates from aromatic aldehydes and acetic acid anhydride.     

Surface Phase Transformations Induced on Fe0.86Mn0.14 by Carbon Ion-Irradiation

Conversion electron Mössbauer spectroscopy and X-ray diffraction have been used to investigate the modifications induced by room-temperature irradiation with 360 keV C^? ions on a Fe_0.86Mn_0.14 alloy. The data show that the irradiation produces γ-FeMn along with an increase in the amount of α-FeMn at the expense of ∈-FeMn, both originally present. The initial distribution of Mn atoms in the α-FeMn martensitic phase is observed to change after irradiation.     

Mössbauer spectroscopy and X-ray diffraction study of the Fe3−x Ti x Al ternary alloys

Mössbauer spectroscopy and X-ray diffraction have been applied to study the structural and magnetic properties of Fe_3?x Ti _x Al alloy system. The distribution of nearest neighborhood of iron atoms as a function of the Ti concentration and formation of the Heusler phase with L2₁ type of structure were investigated.     

Mössbauer spectroscopy of Fe-based nanomaterials

X-ray diffraction, magnetic measurements and Mössbauer spectroscopy were used to study magnetic properties and hyperfine interaction parameters of nanocrystalline (< 10 nm) and bulk bcc Fe, Fe₉₀Ge₁₀, and Fe₇₇Al₂₃ alloys. It has been established that nanocrystalline state does not influence the formation of specific saturation magnetization, Curie temperature, isomer shift and hyperfine magnetic field. No additional sextets in Mö ssbauer spectra as well as special features in temperature dependences of a.c. magnetic susceptibility have been found. A slight increase (～ 20%) of the width of the nanocrystalline Fe Mössbauer spectral lines has been observed.     

Magnetic phase transitions in Fe80-xNixCr20 (14 ⩽ x ⩽ 30) alloy studied by using 57Fe Mössbauer spectroscopy

This paper reports ⁵⁷Fe Mössbauer spectroscopic studies of the polycrystalline samples of the substitutionally disordered, isostructural (fcc), ternary alloy system Fe_80-xNi_xCr₂₀ for x = 30, 26, 19 and 14 in the temperature range of 10–295 K. The data have been analyzed in terms of the magnetic phase transitions occurring in these alloys by examining the temperature dependence of the various Mössbauer parameters like line‐width, center shift, resonance area, distribution of hyperfine field, P(H), and the average hyperfine field 〈H〉. An estimate of the magnetic transition temperature T _C is made for the alloys with x = 30 and 26 and these results are compared with those previously obtained by magnetic measurements and neutron diffraction experiments. The data for the second order Doppler shift have been analyzed to estimate the Debye temperature ΘD for alloys with x = 30 and 26.     

Mössbauer and X-ray study of the Fe 65 Ni 35 invar alloy obtained by mechanical alloying

Fe₆₅Ni₃₅ samples were prepared by mechanical alloying (MA) with milling times of 5, 6, 7, 10 and 11 h, using a ball mass to powder mass ratio of 20:1 and at 280 rpm. The samples were characterized by X-ray diffraction (XRD) and transmission ⁵⁷Fe Mössbauer spectrometry. The X-ray diffraction pattern showed the coexistence of one body centered cubic (BCC) and two face centered cubic (FCC1 and FCC2) structural phases. The lattice parameters of these phases did not change significantly with the milling time (2.866 Å, 3.597 Å and 3.538 Å, respectively). After 10 h of milling, the X-ray diffraction pattern showed clearly the coexistence of these three phases. Hence, Mössbauer spectrometry measurements at low temperatures from 20 to 300 K of this sample were also carried out. The Mössbauer spectra were fitted using a model with three components: the first one is a hyperfine magnetic field distributions at high fields, related to the BCC phase; the second one is a hyperfine magnetic field distribution involving low hyperfine fields related to a FCC phase rich in Ni, and the third one is a singlet related to a FCC phase rich in Fe, with paramagnetic behavior. As proposed by some authors, the last phase is related with the antitaenite phase.     

High-frequency magnetic modulation of recoilless gamma radiation of57Fe

Radio-frequency (rf) magnetic modulation has been used to generate sidebands in⁵⁷Fe Mössbauer spectra of Fe_0.18Ni_0.82 Permalloy foils which have the smallest constant of magnetostriction among Fe?Ni alloys. Sidebands in Mössbauer spectra were observed at 30 MHz and 55 MHz. In addition to the generation of sidebands, the external rf magnetic field was found to alter the line positions of the original six line spectrum. An attempt was made to study acoustic vibrations in the foil by means of X-ray diffraction. The rf magnetic field caused changes in diffraction peak intensities and positions. It was found that X-ray diffraction can be used to study the amplitude of acoustic vibrations in Permalloy foils.     

Magnetic properties of the mixed spinel Mg1+xMnxFe2-2xO4

The structural and magnetic properties of the mixed spinel Mg_1+xMn_xFe_2-2xO₄ system for 0.1<= x <= 0.9 have been studied by means of X-ray diffraction, magnetization, a.c. susceptibility and Mössbauer spectroscopy measurements. X-ray intensity calculations indicate that Mn⁴⁺ ions occupy only octahedral (B) sites replacing Fe³⁺ ions and the added Mg²⁺ ions substitute for A-site Fe³⁺ ions. All samples are magnetic at 12 K displaying Mössbauer spectra that have magnetic sextets coexisting with a central doublet that increases in population with increasing Mn concentration, indicating the presence of short range ordering (clustering). The Mössbauer intensity data show that Mn possesses a preference for the B-site of the spinel over the whole range of concentration. As expected, the hyperfine field and Curie temperature determined from a.c.susceptibility data decrease with increasing Mn content. Magnetization results indicate that on increasing dilution x, the collinear ferrimagnetic phase breaks down at x = 0.3 before reaching the ferrimagnetic percolation limit (x=0.6), as a result of the presence of competing exchange interactions, which is well supported by Mössbauer results. From all the above results, it is proposed that with increasing Mn content from x=0.6 to 0.9, the frustration and disorder increase in the system suppressing the ferrimagnetic ordering, and the system approaches to a cluster spin glass type of ordering at x=0.8 as reflected in the a.c.susceptibility and Mössbauer spectrum.     

Magnetic properties of γ-Fe2O3 nanoparticles encapsulated in surface-treated polymer spheres

Mössbauer and magnetic characterization of polymer-dispersed γ-Fe₂O₃ nanoparticles treated under different chemical processes are reported in this work. X-ray powder diffraction analysis provides a mean particle size of D ~ 8.0 nm. Whereas Mössbauer spectroscopy data suggest the presence of only Fe^3?+? ions, magnetization measurements indicate the occurrence of a freezing phenomenon in agreement with the thermal evolution of Mössbauer spectra. A core–shell model was used to determine a magnetically disordered layer (shell) of d ~ 1.0 nm covering a region of collinear magnetic moments (core). The chemical treatments with H₂O₂ and Na₂S₂O₈ modify notoriously the magnetic response of the polymer-dispersed nanoparticles.     

Mössbauer Investigation of Fe–Mn–Cu Nanostructured Alloys Obtained by Ball Milling

Fe₇₉Mn₂₁, (Fe₇₉Mn₂₁)₉₀Cu₁₀, and (Fe₇₉Mn₂₁)₈₀Cu₂₀, alloys, prepared by high energy ball milling were characterized by Mössbauer spectroscopy, X-ray diffraction and ac-susceptibility. Results indicate that the Cu addition favors the formation of a FCC phase with two different magnetic states at room temperature, i.e., an antiferromagnetic and a paramagnetic one. Thermal evolution of the Mössbauer spectra revealed the occurrence of a magnetic ordering along a wide temperature range. This behavior is probably related to Fe atoms in FCC-Fe(Mn,Cu) phase having different environments and grain size distribution. Thermal dependence of in-phase ac-susceptibility shows that a long range ordering starts at 240 K for the Fe₇₉Mn₂₁ alloy and shifts towards lower temperatures with the Cu content. These results would reflect a long-range magnetic ordering transition with a distribution of ordering temperatures rather than a blocking process of particle single-domains.     

The Fe<Superscript>2+</Superscript> occupancies in the silicates M1 and M2 sites in Chelyabinsk LL5 meteorite determined using XRD and Mössbauer spectroscopy

Study of four Chelyabinsk LL5 ordinary chondrite fragments with different lithology was carried out using X-ray diffraction and Mössbauer spectroscopy with a high velocity resolution. The Fe²⁺ occupancies of the M1 and M2 sites in olivine, orthopyroxene, and clinopyroxene determined using X-ray diffraction and Mössbauer spectroscopy were compared. Distribution coefficients K _D and the temperatures of cations equilibrium distribution T _eq in the olivine and orthopyroxene were evaluated.     

Mössbauer study of incompletely alloyed nanocrystalline Fe100 − x Al x prepared by high energy ball milling

Mechanically alloyed Fe_100???x Al _x powders, with 20≤?x?≤90, have been studied by X-ray diffraction and room temperature ⁵⁷Fe Mössbauer spectroscopy. The milling time was chosen such that complete alloying does not take place. For a fixed milling time of 10 h, the rate of alloying was seen to increase exponentially with increase in Fe content. Mössbauer spectra of all the samples consist of a broad magnetic sextet and a quadrupole doublet. The isomer shifts and quadrupole splitting of the doublets are typical of Al-rich, Fe–Al alloys. The area under the quadrupole doublet is a maximum for x?=?66. Analysis of the Mössbauer spectra indicates the formation off- stoichiometric Fe₃Al phase for x?<?66, while the formation of Fe clusters is largely responsible for the magnetic hyperfine component in x?≥?66 compositions.     

Mössbauer study of phase transition caused by oxidation in the temperature region from 20 to 1000°C in almandine garnets

A Mössbauer investigation has been carried out on garnets from Měděnec and Kti? (Czech Republic). Changes of Fe²⁺ and Fe³⁺ crystallographic sites were observed in these silicate garnets after temperature processing under oxidising atmosphere. The temperature processes were realised from 200 to 1000°C by 100 degrees. The results of Mössbauer experiments are compared with the results of the chemical analysis, X-ray diffraction, infrared spectroscopy, and magnetic susceptibility measurements.     

Electronic and magnetic properties of the iron borate Fe2BO4

Polycrystalline Fe₂BO₄ was prepared by solid state reactions and its electronic and magnetic properties were investigated by Mössbauer spectroscopy and magnetization measurements. The Mössbauer spectra of Fe₂BO₄ below 270 K indicate the presence of Fe²⁺ and Fe³⁺ sites in the structure, in a ratio 1 : 1. Above this temperature electron delocalization sets in between the divalent and trivalent iron ions and Fe^2.5+ states are observed. The temperature dependence of the Mössbauer spectra and magnetization measurements clearly show the onset of magnetic order below 155 K.     

Magnetic Study of Nanocrystalline Ferrites and the Effect of Swift Heavy Ion Irradiation

100 MeV Si⁺⁷ irradiation induced modifications in the structural and magnetic properties of Mg_0.95Mn_0.05Fe₂O₄ nanoparticles have been studied by using X-ray diffraction, Mössbauer spectroscopy and a SQUID magnetometer. The X-ray diffraction patterns indicate the presence of single-phase cubic spinel structure of the samples. The particle size was estimated from the broadened (311) X-ray diffraction peak using the well-known Scherrer equation. The milling process reduced the average particle size to the nanometer range. After irradiation a slight increase in the particle size was observed. With the room temperature Mössbauer spectroscopy, superparamagnetic relaxation effects were observed in the pristine as well as in the irradiated samples. No appreciable changes were observed in the room temperature Mössbauer spectra after ion irradiation. Mössbauer spectroscopy performed on a 12 h milled pristine sample (6 nm) confirmed the transition to a magnetically ordered state for temperatures less than 140 K. All the samples showed well-defined magnetic ordering at 5 K, whereas, at room temperature they were in a superparamagnetic state. From the magnetization studies performed on the irradiated samples, it was concluded that the saturation magnetization was enhanced. This was explained on the basis of SHI irradiation induced modifications in surface states of the nanoparticles.     

57Fe and 151Eu Mössbauer studies of magnetoresistive Europium based cobalt perovskites

Eu_0.8Sr_0.2Fe _x Co_1?x O_3?z CMR perovskites with different iron concentrations (x?=?0, 0.025, 0.075, 0.15, 0.3) were investigated by X-ray diffraction, AC magnetic susceptibility, magnetotransport, as well as ⁵⁷Fe and ¹⁵¹Eu Mössbauer spectrometry. The valence state of europium ions was found to be trivalent, independently of the iron concentration. ⁵⁷Fe Mössbauer spectra and magnetic susceptibility of the investigated perovskites presented complementary results for the magnetic transitions.     

57Fe Mössbauer study of amorphous Fe81B13.5Si3.5C2

The amorphous ferromagnet Fe₈₁B_13.5Si_3.5C₂ (Metglas^® 2605SC) has been investigated with Mössbauer spectroscopy. The hyperfine interaction parameters are studied between 80 and 300 K from which some characteristic properties are deduced. The behaviour of the amorphous alloy at higher temperatures has been studied by the room temperature spectra of annealed samples. After a structural relaxation process, a two step crystallization transformation is observed leading to Fe-Si alloy and Fe₂(B, C). X-ray diffraction of samples annealed at higher temperatures reveals the presence of an orthorhombic Fe-B-Si phase of which the structure changes slightly with annealing temperature.