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This updated and significantly expanded second edition of \"The Mössbauer Effect\" describes the basic physics of the Mössbauer effect and its applications in a variety of fields including physics, chemistry, materials science, biology, mineralogy and archaeology.

Transition metal takes charge The introduction of 'foreign' elements into transition-metal oxides (called chemical doping) can change the valence state of the metal's cations and hence modify the physical properties of the material as a whole. These changes can be dramatic, for example causing high-temperature superconductivity in copper oxides and colossal magnetoresistance in manganese oxides. Youwen Long et al . have identified an oxide system, the perovskite LaCu 3 Fe 4 O 12 , in which changes in valence state occur when charge is shuffled between different cations (iron and copper) in the host structure, rather than via doping. As a result, the material can be reversibly transformed from one possessing iron in an unusually high Fe 3.75+ state (partnered with fairly common Cu 2+ ions) to one possessing rare Cu 3+ ions. These changes are reflected in the magnetic and electronic properties of the material and, intriguingly, the material contracts slightly on being warmed through the transition. The temperature sensitivity of this effect makes it a strong candidate for technological applications. This paper identifies an oxide system where changes in valence state occur as a result of charge being shuffled between different cations in the host structure, rather than via doping, this charge transfer being sensitive to temperature. As a result, the material can be reversibly transformed from one possessing iron in an unusually high Fe3.75+ state to one possessing rare Cu3+ ions. These changes are reflected in the magnetic and electronic properties of the material and, intriguingly, are accompanied by negative thermal expansion. Changes of valence states in transition-metal oxides often cause significant changes in their structural and physical properties 1 , 2 . Chemical doping is the conventional way of modulating these valence states. In ABO 3 perovskite and/or perovskite-like oxides, chemical doping at the A site can introduce holes or electrons at the B site, giving rise to exotic physical properties like high-transition-temperature superconductivity and colossal magnetoresistance 3 , 4 . When valence-variable transition metals at two different atomic sites are involved simultaneously, we expect to be able to induce charge transfer—and, hence, valence changes—by using a small external stimulus rather than by introducing a doping element. Materials showing this type of charge transfer are very rare, however, and such externally induced valence changes have been observed only under extreme conditions like high pressure 5 , 6 . Here we report unusual temperature-induced valence changes at the A and B sites in the A-site-ordered double perovskite LaCu 3 Fe 4 O 12 ; the underlying intersite charge transfer is accompanied by considerable changes in the material’s structural, magnetic and transport properties. When cooled, the compound shows a first-order, reversible transition at 393 K from LaCu 2+ 3 Fe 3.75+ 4 O 12 with Fe 3.75+ ions at the B site to LaCu 3+ 3 Fe 3+ 4 O 12 with rare Cu 3+ ions at the A site. Intersite charge transfer between the A-site Cu and B-site Fe ions leads to paramagnetism-to-antiferromagnetism and metal-to-insulator isostructural phase transitions. What is more interesting in relation to technological applications is that this above-room-temperature transition is associated with a large negative thermal expansion.

The Error and Monitor signals of the Mössbauer driver can be used to infer the true velocity in the acquisition of a Mössbauer spectrum. This information can be recorded to substantially improve the collected data. It can be used to perform quality control of the spectra, validate regions of good linearity and correct non-linearities. In particular the error waveform is essential to account for possible deviations of the channel-to-velocity relation from the expected one. These deviations are mainly due to the physical limitations of the feedback control system. They are almost impossible to anticipate and they vary considerably when modifying the amplitude or shape of the velocity reference, or when modifying the parameters of the closed-loop control system. The sampling of the Error and Monitor waveforms can be carried out with a standard digital oscilloscope, while maintaining a correct synchronization and resolution, necessary for a correct post-analysis. In this paper a method for wave acquisition and reconstruction is proposed. The effects of non-controlled oscillations at the abrupt changes of velocity variation in alpha Fe spectra are discussed. It is also shown how the acquisition can be performed remotely and automatically, without disturbing the measurement or decreasing the efficiency of the spectrometer.

The Mössbauer effect (ME) spectroscopy is a powerful tool to obtain information about magnetic nanoparticles (NP). Here we correlate parameters that can be obtained from a ME spectrum (relative fractions of magnetite and maghemite and the volume dependent parameter λ=KV/kBT ) with other relevant quantities, such as DC saturation magnetization and X-ray diffraction NP mean diameter, D XRD . The study was performed on the decanted pellets of six different batches of NP obtained using the same synthesis procedure. It was observed that λ1/3 presents a linear correlation with D XRD from which the effective anisotropy K for the entire ensemble of the batches could be calculated. The fraction of magnetite retrieved from ME spectra was well correlated to the saturation magnetization. In addition, it was observed that the magnetic response of the supernatant obtained after washing and centrifuging the synthesis product, decreases with λ , according to the fact that larger NP decant more easily during centrifugation.

Surface magnetism of Fe (001) was investigated by the in situ iron-57 probe layer method with a synchrotron Mössbauer source. The observed layer-by-layer internal hyperfine field shows a marked reduction at the surface and an oscillatory behavior with increasing depth in the individual layers below the surface. The calculated layer-by-layer hyperfine interactions (hyperfine field, isomer shift, and quadrupole shift) were consistent with the experimental results. The results give direct evidence for the magnetic Friedel oscillations, penetrating several layers from the Fe (001) surface.

The web-accessible online database (WAD) of the Mössbauer Effect Data Center (MEDC) is one of the worldwide available information services provided by MEDC to the scientific community. It is based on the uniquely wide scope Mössbauer spectroscopy database that has been compiled and maintained by MEDC since the 1960’s. Following enhancements applied to the capabilities of the MEDC core database in connection with the development of a new database management software named “MEDC DBM”, the development of a new web-accessible online database (MEDC WAD) was started in 2019. Here we introduce the current state and the main features of the newly developed MEDC WAD system with emphasis put on its novel and rather unique attributes that can effectively aid the scientific research process in the field of Mössbauer spectroscopy.

Mössbauer measurements on single crystal absorbers at room and at low temperatures were performed. The results are fully consistent with previously published reports by other groups. Spectra of single crystals were simultaneously analyzed including magnetic dipole and electric quadrupole interactions. The analysis shows that there is a small component of magnetic moments perpendicular to the magnetic easy axis. Mössbauer data seem not agree with commonly accepted ferrimagnetic structure of GaFeO3.

The Mössbauer spectroscopy database compiled and maintained by the Mössbauer Effect Data Center (MEDC) is a unique, wide-scope Mössbauer-spectroscopy related information resource, which forms the basis of information services provided by the Mössbauer Effect Data Center to the worldwide scientific community. The Mössbauer Effect Reference and Data Journal (MERDJ) and the Mössbauer Web Access Database (MWAD), both published by MEDC, are widely known examples of the services that rely on the MEDC database. In recent years a further improvement of these services, especially that of MWAD, has been envisaged, and as a first step of the corresponding process the further development of the MEDC database was started. In the present work we introduce the main features of the MEDC database and the steps that have been already taken in the frame of its further development. Implications of the work regarding the associated services are also presented.

A series of high iron content boro-phosphate glasses having composition of 30P 2 O 5 -70B 2 O 3 -xFe 2 O 3 );0 ≤ x ≤ 80 wt% was prepared by conventional melt quench method. Mössbauer effect (ME), infrared (IR) and electron spin resonance (ESR) were used to study the behavior of iron brought into borophosphate glass and its effect on the structure of the glass. The results of the glasses containing from 10 to 80 wt% Fe 2 O 3 indicated that iron is present in the glass in the form of Fe 3+ and Fe 2+ , i.e. in tetrahedral and various octahedral symmetric sites. Electron paramagnetic resonance (EPR) spectra were utilized to investigate the glass structure. The analysis shows a well-defined signal at g = 2.04 characteristics for Fe 3+ ions and the intensity increases with increasing Fe 2 O 3 concentration before gamma irradiation. After exposing the samples to different doses of gamma irradiation up to 30 kGy; the EPR signal intensity decreases for the samples with a low Fe 2 O 3 concentration (i.e. 10% and 40%), which can be used as radiation indicators. For glass with high iron concentrations above 40%, the intensity of the EPR signal remains approximately constant and therefore, high iron concentrations of this glass can be used for radiation protection purposes.

Two spinel ferrite samples Ni 0.7 Zn 0.3 Ga y Fe 2– y O 4 ( y = 0.5, 1.0) were prepared by both ceramic and citrate methods. X-ray diffraction patterns indicated a single phase of cubic structure for all the samples that have a space group Fd-3m. Rietveld analysis using MAUD software for all samples showed that the lattice parameter ( a ) decreases, while oxygen parameter ( U ) and strain ( ɛ ) increase by increasing the amount of Ga. A marked increase in the frequency bands in both the tetrahedral and octahedral sites was observed in the vibrational frequency bands of Fourier transform infrared spectra. Mössbauer effect (ME) spectra recorded at room temperature for the bulk sample (prepared by ceramic method) with lower concentrations of Ga 3+ ( y = 0.5) consist of two Zeeman sextets. ME spectra for the other bulk sample ( y = 1.0) and the two samples in nanoscale (prepared by citrate method) can be fitted by one and two doublets due to the paramagnetic and superparamagnetic behaviour, respectively. Vibrating sample magnetometer measurements showed that the saturation magnetization ( M s ) obtained from the hysteresis loop is decreased by increasing Ga 3+ concentration for all the samples. The coercivity ( H c ) is inversely proportional to the particle size ( D ) for bulk samples. Nevertheless, H c of the nanoscale samples enhanced by increasing the particle size. The size dependence of H c is an indication of the superparamagnetic characteristics supported by ME. The ac electrical conductivity (ln σ ), dielectric constant ( ε ′) and dielectric loss tangent (tan δ ) were studied at different frequencies and temperatures for the investigated samples. The obtained results showed that the conductivity for all samples increases with increasing temperature in a behaviour similar to that of the most semi-conductor materials.