Mössbauer Studies on Magnetic Multilayers

Hyperfine Interactions - Mössbauer spectroscopy is a useful tool to study the magnetic properties of multilayers from microscopic viewpoints. Recent experimental results relating to the issues...     

How can Mössbauer Spectrometry Contribute to the Characterization of Nanocrystalline Alloys?

A controlled annealing of amorphous precursors represents a simple way of obtaining nanocrystalline alloys featuring interesting magnetic properties suitable for technical applications. They stem from the presence of crystalline nanograins embedded in the amorphous residual matrix which determine the resulting macroscopic parameters. In order to understand correlation between the microstructure and the resulting magnetic behaviour, Mössbauer spectrometry is used as a method of local probe analysis. Possibilities of this technique are discussed and representative examples of investigation of NANOPERM-type nanocrystalline alloys are provided.     

Magnetic Properties of Nanoparticles of Antiferromagnetic Materials

Hyperfine Interactions - The magnetic properties of antiferromagnetic nanoparticles have been studied by Mössbauer spectroscopy and neutron scattering. Temperature series of Mössbauer...     

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.     

Mössbauer study of some biological iron complexes

Some biological complexes containing iron are investigated experimentally at room temperature using the Mössbauer resonance. The complexes show quadrupole doublet and Kramer’s degeneracy is found to exist. The electric field gradient, difference ins-electron densities and quadrupole coupling constant have been calculated in each case. These parameters are used to obtain information on the surroundings of the Mössbauer atom     

Magnetic Relaxation and Its Relation to Magnetoresistance in FeCr2S4 Spinel

Hyperfine Interactions - The temperature dependence of the local electronic and magnetic state of iron in the chalcogenide spinel FeCr2S4 has been studied in detail around the Curie temperature...     

On the Tannic Acid Interaction with Metallic Iron

The reaction between tannic acid and metallic iron was studied using infrared and Mössbauer spectroscopy. Iron converts to sparingly soluble and amorphous ferric tannate complexes. The degree of conversion was followed from 1 day to 6 months. In the very early stages of reaction the product consists of a mono-type complex, while in the later stages a mixture of mono- and bis-type complexes were formed. The conversion reaction of metallic iron to tannate complexes follows a first-order reaction kinetics.     

Magnetic Properties of the Mechanically Alloyed (Fe0.85Mn0.15)0.3Cu0.7 System

Samples of nominal composition (Fe_0.85Mn_0.15)_0.3Cu_0.7 were prepared by mechanical milling starting from pure element powders. In order to elucidate the effect of the alloying time upon the magnetic properties of the system, milling times ranging from 1 hour up to 72 hours were considered. The phase distribution present on the as-milled materials was identified from the analysis of X-ray diffraction data. The room temperature magnetic properties of the samples were studied by means of ⁵⁷Fe Mössbauer spectroscopy and vibrating sample magnetometry, whereas their low temperature magnetic behavior was characterized through magnetic susceptibility measurements. The results evidenced a strong dependence of the magnetic properties on the milling time and, concretely, the occurrence of a superparamagnetic behavior in the long-time-milled samples for which an extended solid solution was obtained. This fact is attributable both to the obtained crystallite sizes, which resulted to be of the order of a few nanometers, and to a milling-driven increase of the lattice parameter.     

237Np and 57Fe Mössbauer study of NpFeGa5

⁵⁷Fe and ²³⁷Np Mössbauer ōmeasurements have been performed for NpFeGa₅, which is one of the so-called neptunium 1-1-5 compounds. The ⁵⁷Fe Mössbauer spectra below T _N = 118 K show the magnetically ordered state. The magnitude of the hyperfine magnetic field at the ⁵⁷Fe nucleus is determined to be 1.98 ± 0.05 T at 10 K. From the ²³⁷Np Mössbauer spectrum at 10 K, the hyperfine magnetic field at the ²³⁷Np nucleus is 203 T and the hyperfine coupling constant is determined to be 237 T/μ_B using the Np atomic magnetic moment of 0.86 μ_B determined by the neutron diffraction study.     

Mössbauer Spectroscopy in the Characterisation of Polymetallic Cluster Compounds: a Triple Mössbauer Study of (PPh4)[Fe2Ir2(CO)12{μ3-Au(PPh3)}]

The iron meteorites Sikhote–Alin, Bilibino, Chinga and Dronino with different Ni concentration and terrestrial age were studied by Mössbauer spectroscopy. Different Mössbauer hyperfine parameters were determined for studied meteorites and possible Fe–Ni phases were supposed.     

Magnetic Phases in Alloys and Nanostructured Systems

Hyperfine Interactions - The structure of nanocrystalline and nanostructured iron-containing systems is discussed on the basis of the hyperfine interactions observed by 57Fe Mössbauer...     

Magnetic properties of Martian olivine basalts studied by terrestrial analogues

Here we present a comparison study of terrestrial olivine basalt and relatively un-weathered basalt studied by the Mars Exploration Rover Spirit on Mars. The Mössbauer spectra of terrestrial olivine basalt exhibit some characteristics that can also be seen in the Mars spectra. The results from Mössbauer spectroscopy on Mars indicate that the olivine in the rocks has undergone alteration at high temperatures (600–1,000°C), a process known to give rise to anomalously magnetic rocks on Earth. This suggests that if the rocks at Gusev crater had solidified in an external magnetic field of terrestrial magnitude, these would have become highly magnetic enough to explain the presence of magnetic anomalies on Mars.     

Magnetic behavior of the oxide spinels: Li0.5Fe2.5−2x Al x Cr x O4

In order to study the effect of substitution of Fe³⁺ by Al³⁺ and Cr³⁺ in Li_0.5Fe_2.5O₄ on its structural and magnetic properties, the spinel system Li_0.5Al _x Cr _x Fe_2.5?2x O₄ (x=0.0, 0.2, 0.4, 0.5, 0.6 and 0.8) has been characterized by X-ray diffraction, high field magnetization, low field ac susceptibility and ⁵⁷Fe Mossbauer spectroscopy. Contrary to the earlier reports, about 50% of Al³⁺ is found to occupy the tetrahedral sites. The system exhibits canted spin structure and a central paramagnetic doublet was found superimposed on magnetic sextet in the Mössbauer spectra (x>0.5).     

The Unusual Mössbauer Spectrum of Beryl

The Mössbauer spectra of several aquamarine samples have been obtained in the temperature range of 4.2–500 K. A common feature observed in all room-temperature spectra is the presence of an asymmetric Fe²⁺ doublet (ΔE _Q～2.7 mm/s, δ～1.1 mm/s), with a very broad low-velocity peak. This asymmetry is not caused by preferred orientation since the spectrum collected under the magic angle did not show any difference in the line intensities, nor is it caused by the superposition of a Fe³⁺ doublet. At 4.2 K the spectrum of a deep-blue beryl could be well fitted with three symmetrical doublets, with the major Fe²⁺ doublet accounting for 87% of the total spectral area. At 14 K the symmetry remains, but at 30 K the low-velocity peak is again broad. Surprisingly, the spectrum at 500 K also shows a broad, but symmetrical doublet, with a clear splitting of the lines indicating the presence of at least two Fe²⁺ components. The room-temperature spectrum obtained after the 500 K run shows the same features as before the heating. A meaningful fit for the room-temperature spectrum, as well as an explanation for the temperature dependence of the Mössbauer spectra, are discussed.     

Mössbauer effect in natural strunzite, ferristrunzite and ferrostrunzite

The temperature dependence of the ferric and ferrous hyperfine fields in natural samples of strunzite, ferristrunzite and ferrostrunzite is determined by Mössbauer spectroscopy between 4.2 K and their magnetic transition temperatures (T _N), i.e. 50.5±0.5 K, 43.0±0.5 K and 44.0±0.5 K respectively, which are determined by Mössbauer thermoscanning. Two dominating magnetically split ferric subspectra were consistently present in all of the samples and are related to the Fe(1) and Fe(2) sites in the crystallographic structure, but an unambiguously assignment to a specific site is not possible. The difference between the corresponding hyperfine fields is very small. In the strunzite sample these fields are well defined and rather weakly dependent of temperature. In the other samples the corresponding hyperfine fields are more distributed especially at higher temperatures (below T _N). The relative contribution in the spectra of the third magnetic ferric component differs strongly between the samples and is assigned to ferric ions at the Mn site. At the lowest temperatures applied, its hyperfine field exceeds all other field values, but it decreases rather rapidly with increasing temperature, in so far that the corresponding spectral lines make a crossover with the lines of the other ferric subspectra. The magnetically split spectra of ferrostrunzite consist additionally of a ferrous magnetic component, which could be successfully analysed by introducing two magnetically split ferrous subspectra, which strongly overlap with each other but also with the ferric components. At higher temperatures in the magnetic region all subspectra overlap more and in the case of ferri- and ferrostrunzite the ferric hyperfine fields were distributed over a wider range.     

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.     

New in-beam Mössbauer spectroscopy station at the Budapest Research Reactor

We report about a new in-beam Mössbauer station which is intended to utilize the cold neutron source and guide system installed on the 10th beam line of the Budapest Research Reactor. This new in-beam facility enables us to broaden the number of nuclides accessible for Mössbauer studies in various materials. In this article we describe our new system and summarize the possibilities of its application to Mössbauer spectroscopy.     

Influence of the Interfaces on Magnetic Properties of Fe/Ag and Fe/Cu Multilayers Prepared by Sputtering

Hyperfine Interactions - Dependence of magnetic behavior of ultrathin Fe layers on the width of the interfaces was investigated by using dc-magnetron sputtering to grow (Fe(110)/Ag(111))...     

Influence of Electron Delocalization on the Magnetic Properties of Iron Ludwigite Fe3O2BO3

⁵⁷Fe Mössbauer spectroscopic studies of iron ludwigite Fe₃O₂BO₃ performed between 4 and 450 K allow the discussion of magnetic spin arrangements and the dynamics of electronic configurations of iron. The observed magnetic transitions are related to charge ordering.