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The method of scanning conversion electron Mossbauer spectroscopy has been proposed, which suggests the anode in the conversion electron detector to be made in the needle form. It has been shown that it is possible to scan the sample surface to obtain information on the structural-phase state of the local near-surface layers of the studied materials. The methods of transmission Mossbauer spectroscopy (MS), integral (ICEMS) and scanning (SCEMS) conversion electron Mossbauer spectroscopy have been used to study the iron nanotubes prepared by template synthesis using the track membranes. According to MS data, ~ 90% of iron in the nanotube structure is in a chemically free state. It follows from the ICEMS and SCEMS results that in the near-surface layers of nanotubes the iron cations are predominantly localized in the structure of hydroxides. The differences in the orientation of the magnetic moments in the bulk and near-surface layers have been established.

We studied the growth of iron mononitride (FeN) thin film on a titanium mononitride (TiN) underlayer. FeN samples with a zinc blende (ZB)-type structure were deposited using reactive magnetron sputtering with and without the TiN underlayer on an amorphous quartz substrate. Combining x-ray diffraction, conversion electron Mossbauer spectroscopy, nuclear forward scattering and N K-edge x-ray absorption near edge spectroscopy measurements, we probed the long range and the local structure in our samples. FeN films are known to exhibit structural and magnetic imperfections. With the TiN underlayer such imperfections get reduced to a large extent. By studying films of different thicknesses, the origin of imperfections present in FeN films has turned out to be correlated with the film growth process. Obtained results are presented and discussed in this work.

We have implanted ZnO thin film with 40 keV Fe+ ions to a high fluence of 1.25 × 1017 ions/cm2. Elemental and magnetic phase compositions were investigated by XRD, XPS, CEMS, and VSM methods. The Fe-implanted ZnO film reveals strong ferromagnetism at room temperature. The implanted iron ions are found in different valence states of Fe2+ and Fe3+. It was attributed to the formation of paramagnetic and ferromagnetic iron-based phases. The ferromagnetism is explained with the formation of a magnetic ordered solution of iron ions in ZnO matrix. Post-implantation annealing in a high vacuum results in the decrease of magnetism due to the formation of magnetite nanoparticles.

International audience; Here we reported an about 2 at.% Fe-implanted p-type 4H-SiC Diluted Magnetic Semiconductor (DMS). Scanning Transmission Electron Microscopy (STEM) and Atom Probe Tomography (APT) techniques were used to investigate the origins of ferromagnetic behavior. Nanoparticles (1–9 nm) were identified to be Fe3Si, Fe2Si, Fe5Si3, Fe3Si2, FeSi and FeSi2 phases, the distribution of which is related to Fe distribution. The magnetic properties were studied by Conversion Electron Mössbauer Spectroscopy (CEMS) and Superconducting Quantum Interference Device (SQUID) techniques. The contributions of these Fe-silicides to the ferromagnetism are thus discussed from a quantitative perspective.

The structural and magnetic properties of disordered Fe2CrAl intermetallic thin film obtained from thermal annealing of [Al17 A/57Fe25 A/Cr13 A]x20 multilayer have been studied. The combination of X-ray reflectivity, X-ray diffraction, DC magnetization, and conversion electron Mossbauer spectroscopy are used to characterize the as-deposited and annealed multilayers. The structural and conversion electron Mossbauer spectroscopy studies show that on annealing [Al17 A/57Fe25 A/Cr13 A]x20, multilayer at 773 K, a thin film of Fe2CrAl phase is obtained. DC magnetization studies show the formation of an excellent soft magnetic material with coercivity in the range of 2–22 Oe and saturation magnetization of ∼500–900 emu/cm3. The Curie temperature is found to be much higher than that of its bulk. Disordered Fe2CrAl phase formed after annealing at 833 K for 3 h is highly stable and totally reversible against high temperatures. We believe that this composition in thin film form, with an excellent soft magnetic properties is a suitable material for many multi-functional applications.

Sputter deposited Mg2FexSi1-x films of 250 nm thickness have been investigated by means of Mossbauer spectroscopy. While non-hydrogenated films are characterized by a quadrupole split doublet, hydrogenated regions show a singlet with reduced isomer shift. The relative areas of the spectra reflect the relation between loaded and unloaded regions prepared at the same loading conditions.

The present work reports the preparation of 5 μm wide and 10 μm grating periodicity patterned [ F e ( 2.0 n m ) / P t ( 2.5 n m ) ] X 10 multilayer and its thermal annealing behavior. Intermixing across the Fe and Pt layers is observed with vacuum annealing at 650 K resulting in the formation of disordered face centered cubic (FCC) and ordered L 1 0 face centered tetragonal (FCT) FePt phases. The longitudinal magneto-optical Kerr effect (L-MOKE) hysteresis loop, measured from the single 5 μm FePt stripe shows double loop behavior indicating the presence of two magnetic phases, one with the low coercivity ( H C ) and the second one with the higher H C values. This could be due to the presence of disordered FCC and ordered L 1 0 FCT phases of FePt, known to be soft and hard magnetic phases. Conversion electron Mossbauer spectroscopy of the annealed sample shows the presence of FCC and FCT FePt phases corroborating the x-ray diffraction and MOKE measurements. The hysteresis loop of the soft phase shows the exchange bias effect with the remnant state of the hard magnetic phase as initial condition akin to the exchange bias as observed in conventional ferromagnetic - antiferromagnetic bilayers.

The effect of heat treatment on the structural and magnetic properties of bilayered FeOx/Fe thin films grown by pulsed laser deposition on pre-oxidized amorphous SiO2/Si substrates has been studied. Post-deposition vacuum thermal annealing leads to remarkable changes in the structural and magnetic properties of the FeOx layer, which has been investigated by the combination of scanning electron and atomic force microscopy, Raman scattering spectroscopy and conversion electron Mossbauer spectroscopy. FeOx layer deposited at room temperature on top of the polycrystalline Fe underlayer is amorphous with the smooth surface (root mean square roughness ~ 0.5 nm). Vacuum thermal annealing of the FeOx/Fe stack at T = 500 °C leads to the formation of a polycrystalline Fe3O4/Fe thin film structure with the magnetite nucleation centers of an average size of 100 nm. The formation of the exact magnetite phase depends on the annealing conditions as shown by in-situ Raman and Mossbauer spectroscopy investigations.

The room temperature 57Fe Mossbauer and XPS spectra were measured for polycrystalline Fe0.88Cr0.12 and Fe0.85Cr0.15 alloys which were exposed to air at 870 K. The spectra were collected using three techniques: the transmission Mossbauer spectroscopy (TMS), the conversion electron Mossbauer spectroscopy (CEMS) and the X-ray photoelectron spectroscopy (XPS). The combination of these experimental methods allows to determine changes in atomic composition in the bulk, in the subsurface layer and on the surface of the studied alloys. The results obtained by XPS confirm the strong chromium segregation process on the surface of Fe0.88Cr0.12 and Fe0.85Cr0.15 alloys. At the same time, the CEMS and TMS measurements reveal that in both samples, during the exposure to air at 870 K, iron oxides were formed. These findings lead to conclusion that the formation of a stable Cr oxide film on the surface of Fe0.88Cr0.12 and Fe0.85Cr0.15 alloys, does not prevent atmospheric corrosion at 870 K. Moreover, the observed by CEMS and TMS, oxidation process of iron atoms is slower for Fe0.88Cr0.12 than for Fe0.85Cr0.15. This fact is in agreement with XPS results which show that Cr surface segregation process is more effective in case of Fe0.88Cr0.12.

This study aims at a crystallization process of metallic glass ribbon. An impact of the magnetic interaction upon the crystallization process is reported. Amorphous ribbon composed of Fe 76 Mo 8 Cu 1 B 15 has been covered by sputtered Co layer in the range 0–100 nm. Deposited Co layers were investigated by magneto-optical Kerr measurements which confirm their ferromagnetic character. The amorphous ribbons with and without Co cover layer were thermally treated under the elevated temperature. Afterwards, the degree of crystallization was determined using transmission Mossbauer spectroscopy and conversion electron Mossbauer spectroscopy measurements at room temperature. Sputtered cobalt layer significantly boosts development of nanograins in the whole amorphous matrix. It was revealed that the crystallization enhancement was caused by magnetic impingement of ferromagnetic Co layer with the thickness higher than 30 nm.

57 Fe conversion electron Mossbauer spectroscopy was used to study the effect of swift heavy ion irradiation on electrochemically deposited metallic pure α-iron. We succeeded in preparing superparamagnetic iron by irradiating the electrochemically prepared thin α-iron films using 247 MeV Kr ions with a fluence of 1×10 13 ion cm −2 which converted 50% of crystalline α-iron into amorphous and superparamagnetic phases, the latter being >20%. The results are discussed in terms of the thermal spike model for the formation of the amorphous phase which could be essential for the formation of superparamagnetic iron.

The room temperature studies of polycrystalline iron exposed to air at various temperatures were performed using: the transmission Mossbauer spectroscopy (TMS), the conversion electron Mossbauer spectroscopy (CEMS) and the X-ray photoelectron spectroscopy (XPS). The unique combination of these techniques allows to determine changes of chemical composition and content of iron oxides simultaneously on the surface region, the 300 nm pre-surface region and the bulk of the samples. The results show that the chemical composition of samples changes significantly and it is strongly dependent on temperature at which the iron sample is exposed to air as well as on investigated region.

Hematite (α-Fe 2 O 3 ) polycrystalline thin films of different thicknesses were produced by thermal oxidation in air atmosphere from Fe metallic thin-films deposited by radio frequency (RF) sputtering technique. X-ray diffraction (XRD) patterns confirm the formation of hematite phase in all samples and indicate that the mean grain size decreases as the film thickness becomes thinner. Conversion electron Mossbauer spectroscopy (CEMS) spectra at room temperature show magnetic splitting (six line patterns). It is determined that the resonance peaks become broader and asymmetric as the film thickness decreases. This finding was associated with the structural disorder introduced by the thickness reduction. Magnetization as a function of the magnetic field curve obtained at 300 K shows the presence of a weak-ferromagnetic contribution, which was assigned to the large density of decompensated spins at the films surface. From the magnetization vs. temperature curves it has been determined that the Morin transition temperature (T M ) is shifted from ~ 240 K to ~ 196 K, meanwhile it becomes more broadened as the film thickness decreases. X-ray photoelectron spectroscopy (XPS) measurements show the presence of Fe 2 + ions coexisting with Fe 3 + ions whose population increases as the film becomes thinner. The density of chemisorbed oxygen increases as the film thickness is reduced in agreement with the results obtained from the other measurements in this work.

Multilayers of 0.4 nm Fe and 5 nm Ag with repetition number, n =1, 2, 5, 10 and 20 were prepared by vacuum evaporation onto Si wafer. The blocking temperature was determined by measuring the field cooled and zero field cooled magnetization curves with a SQUID magnetometer and it was found to increase by almost an order of magnitude from around 20 K for the single Fe layer sample up to around 160 K for n =20. Significant increase of the average size of the superparamagnetic Fe grains by increasing the number of the Fe layers was excluded by conversion electron Mossbauer spectroscopy measurements of the paramagnetic state. The role of the dipole–dipole interactions and their interplay with the out-of-plain magnetic anisotropy in the variation of the blocking temperature has been investigated by Monte-Carlo simulations.

The effects of plasma current density on phase formation of plasma nitrided H13 steel, and on the consequent tribological properties were investigated. The combination of plasma current density and sample temperature formed several different phases, whose relative abundance influenced the friction and wear behaviors. The phases were identified using conversion electron Mossbauer spectroscopy and grazing incidence X-ray diffraction. Elemental depth profiles were determined with glow discharge optical emission spectroscopy and nuclear reaction analysis. The coefficients of friction and the dimensional specific wear rates were evaluated in pin-on-disk tests. Reduction of the coefficient of friction in the initial stages of the tests was attributed to the presence of cementite, formed in certain conditions of plasma processing. Specific wear rates were quantified with profilometry of the wear scars and indicated ten times lower values, when compared to the non-nitrided samples.

Conversion electron Mossbauer spectroscopy (CEMS) measurements have been performed on single crystal Al 2 O 3 implanted with 56 Fe and 57 Fe ions to a total fluence of 1.2 × 10 16 /cm 2 , corresponding to a concentration of approx. 4 at.%. The CEM spectrum in the ‘as-implanted’ state is in good agreement with earlier studies. Annealing at temperatures above 600 °C resulted in significant changes, with the spectra after the annealing at T A ≥ 800 °C displaying paramagnetic doublets characteristic of superparamagnetic nanoclusters. Magnetization curves of the annealed sample show hysteresis loops with zero coercive field while the analysis of low temperature magnetic isotherms in terms of the Langevin function for superparamagnetic particles yields an average radius of 2–3 nm for the Fe clusters.

The phases formed in iron nitride thin films grown on Si wafers by magnetron sputtering with pulsed power supply were investigated. X-ray diffraction and conversion electron Mossbauer spectroscopy showed that in addition to the expected temperature dependence, there was an influence of film thickness on phase composition. All films of several thickness deposited at room temperature were composed of a mixture of mononitrides, namely γ″-FeN, γ‴-FeN, and a third phase compatible with a hexagonal wurtzite-type FeN. Thin films (20 nm) deposited at higher temperatures showed increasing amounts of e-Fe2.1N, becoming single phase above 400 °C, and staying single e-phase up to 500 °C. Thicker films (200 nm) showed the presence of e-Fe2.1N already at 100 °C, became single-phase e-Fe2.1N at 300 °C, and single phase γ′-Fe4N at 500 °C.

Depth-dependent spin rotation of the Fe spins upon magnetisation reversal of the ferromagnetic layer in polycrystalline Fe/FeMn exchange-biased bilayers was investigated by using 57Fe probe layers and angular hysteresis loops constructed from in-field 57Fe conversion electron Mossbauer spectroscopy (CEMS) measurements and magnetometry. Our results provide evidence for the formation of an exchange-spring-like domain wall structure inside the ferromagnetic Fe layer during magnetisation reversal along the forward branch of the hysteresis loop (H values varying from positive to negative), and coherent reversal along the recoil branch (H varying from negative to positive). This result implies asymmetric magnetisation reversal for each branch of the hysteresis loop, as indicated by depth-resolved CEMS and vibrating sample magnetometry. These results are relevant for the development of more precise quantitative models for exchange bias in polycrystalline metallic systems with Mn-based antiferromagnets such as those used in spintronic applications.

In this study, we analysed Fe/Cr multilayers that had been modified by Bi, In, and Pb surfactants. Their structure, morphology and interface roughness were investigated using low-energy electron diffraction, Auger electron spectroscopy (AES), X-ray reflectivity and conversion electron Mossbauer spectroscopy (CEMS). The magnetic and magnetotransport properties of the multilayers were studied by measuring the Kerr effect and four-point magnetoresistance, respectively. We observed that the Bi surfactant caused a slight interface smoothening while the introduction of In and Pb surfactants had a negative influence on the epitaxial growth of Fe and Cr, which were associated with an increase of interface roughness. These changes did not destroy the layer continuity, which was confirmed by AES measurements. The magnetic measurements revealed an antiferromagnetic coupling of the Fe layers for the as-deposited sample as well as for the Bi and Pb-modified multilayers and its partial reduction for the In-modified sample. We observed that the increase of interface roughness that had originated from atom intermixing resulted in a reduction of the giant magnetoresistance. In these investigations in which CEMS studies were used, we were able to distinguish between the interface roughness that was caused by atom intermixing and interface corrugation.

Mossbauer spectroscopy has been used as a novel characterization technique to investigate Fe charge states, Fe complexes and hyperfine interaction parameters of different phases in WC-10Fe and WC-10(FeNi) materials sintered at three different temperatures (1350, 1430 and 1510 °C). The materials were characterized using standard cemented carbide quality control, and spectroscopic techniques to evaluate the structural changes and magnetic effects of the binder. The WC-10Fe grade had the highest Vickers hardness ranging from 1282 to 1320 HV30, for the different sintering temperatures. X-ray diffraction data showed the presence of WC and the metal binder phase, α-Fe and γ-FeNi. Transmission Mӧssbauer spectroscopy spectra obtained for the milled powders revealed only the α-Fe phase with a hyperfine magnetic field, Bhf ~33 T. Conversion electron Mossbauer spectroscopy on the sintered compacts revealed the presence of multiple fields, suggesting the possibility of minor phases present in the binder which were not detected using X-ray diffraction. The corresponding spectra for the sintered WC-Fe grades exhibited two magnetic fields with hyperfine parameters of ~33 T and ~17 T, respectively. These fields were assigned to α-Fe with some W atoms in solution and a W-rich Fe phase, respectively. The Mӧssbauer spectrum for the FeNi binder sample at the lowest sintering temperature of 1340 °C showed a paramagnetic doublet with an isomer shift, δ = −0.08 mm/s and electric quadrupole splitting, ∆EQ = 0.00 mm/s and a weak hyperfine magnetic field, Bhf = 15.7 T. The doublet has been assigned to γ-FeNi and the magnetic component to a W-rich γ-FeNi phase. For the higher sintering temperature, a distribution of magnetic fields (~33 T, 25 T and 9 T) was evident in the Mossbauer spectrum. These magnetic fields were tentatively assigned to multiple W-rich γ-FeNi phases.

The formation of Fe silicides in surface ripple patterns, generated by erosion of a Si surface with keV Ar and Xe ions and simultaneous co-deposition of Fe, was investigated with conversion electron Mossbauer spectroscopy, atomic force microscopy and Rutherford backscattering spectrometry. For the dot and ripple patterns studied, we find an average Fe concentration in the irradiated layer between 6 and 25 at.%. The Mossbauer spectra clearly show evidence of the formation of Fe disilicides with Fe content close to 33 at.%, but very little evidence of the formation of metallic Fe particles. The results support the process of ion-induced phase separation toward an amorphous Fe disilicide phase as pattern generation mechanism. The observed amorphous phase is in agreement with thermodynamic calculations of amorphous Fe silicides.

Structure, composition and chemical behavior of co-sputtered Fe–Nb thin films are analyzed by different techniques, as conversion electron Mossbauer spectroscopy, x-ray photoelectron spectroscopy and x-ray diffraction. It is shown that oxygen is determinative in hindering the Fe–Nb alloy formation and, as a result, Fe 1 −x O and Nb 2 O 5 occur in significant amounts, even in vacuum. In spite of the oxygen role, a Fe–Nb alloy is formed in little amounts, which increase as the Nb content is increased. The increase of the Nb content is also related with the increase of Fe 1 −x O and with a decreasing of the metallic Fe present. Mossbauer data indicate the Fe–Nb phase present is the Fe 2 Nb Laves phase.

The coexistence of superconductivity and ferromagnetism is investigated in granular Sn-Co nanocomposites. The nanocomposites have been prepared by co-deposition of Sn atoms and Co clusters, the morphology and composition of which can be tuned by varying the deposition rate of Co clusters relative to Sn atoms. Flat isolated Sn islands are obtained at zero or low Co cluster flux, while granular nanocomposites are formed with increasing Co cluster flux, reaching Co concentrations up to 44 vol.%. Interfaces with a low electronic transparency between superconductor and ferromagnet are obtained by a combination of the granular nature of the nanocomposites and the formation of Sn-Co alloys at the Sn/Co interfaces. The structure and composition of the nanocomposites have been thoroughly characterized by atomic force microscopy, x-ray diffraction and conversion electron Mössbauer spectroscopy. Over the entire Co concentration range, the hybrids show a ferromagnetic response. The superconducting phase boundary and the Meissner response depend on the morphology and composition of the nanocomposites. In particular, the superconducting critical temperature decreases with increasing Co concentration, while the Meissner response varies from a reversible to a strongly hysteretic behaviour depending on the morphology of the samples with different Co content. The persistence of superconductivity at high Co concentrations is attributed to a suppression of the superconducting proximity effect in these nanocomposites, which is ascribed to the low interface transparency between the Sn and Co components that make up these hybrid systems. publisher: Elsevier articletitle: Coexistence of superconductivity and ferromagnetism in cluster-assembled Sn–Co nanocomposites journaltitle: Journal of Alloys and Compounds articlelink: http://dx.doi.org/10.1016/j.jallcom.2015.03.007 content_type: article copyright: Copyright © 2015 Elsevier B.V. All rights reserved. ispartof: Journal of Alloys and Compounds vol:637 pages:509-516 status: published

A systematic study of the iron–silicon interfaces formed upon preparation of (Fe/Si) multilayers has been performed by combination of modern and powerful techniques. Samples were prepared by thermal evaporation under ultrahigh vacuum onto a Si(1 0 0) substrate. The morphology of these films and their interfaces was studied by a combination of scanning transmission electron microscopy, X-ray reflectivity, angle resolved X-ray photoelectron spectroscopy and hard X-ray photoelectron spectroscopy. The Si-on-Fe interface thickness and roughness were determined to be 1.4(1) nm and 0.6(1) nm, respectively. Moreover, determination of the stable phases formed at both Fe-on-Si and Si-on-Fe interfaces was performed using conversion electron Mössbauer spectroscopy on multilayers with well separated Si-on-Fe and Fe-on-Si interfaces. It is shown that while a fraction of Fe remains as α-Fe, the rest has reacted with Si, forming the paramagnetic c-Fe1−xSi phase and a ferromagnetic Fe rich silicide (DO3 type phase). We conclude that the paramagnetic c-Fe1−xSi silicide sublayer is identical in both Si-on-Fe and Fe-on-Si interfaces, whereas an asymmetry is revealed in the composition of the ferromagnetic silicide sublayer., The financial support of the Spanish MINECOMAT2011-23791, the President of Russia Grant (NSh-1044.2012.2), RFFI Grant 13-02-01265, the Ministry of Education and Science of Russian Federation (14.604.21.0002 and 02G25.31.0043), Aragonese DGA-IMANA E34 (cofunded by Fondo Social Europeo) and that received from the European Union FEDER funds is acknowledged. L.B.R. acknowledges the Spanish MINECO FPU 2010 grant.

Atomic intermixing processes in relation to structural aspects and phase formation in Be based thin films subjected to different annealing treatments simulating the case of re-deposited layered structures on plasma facing components in nuclear fusion devices are reported. Accordingly, bilayers of Be/W and Be/C have been deposited on Si(0 0 1) substrates with Fe buffer layers. The Fe films have been prepared by radiofrequency sputtering and further processed by annealing in hydrogen atmosphere at 300 °C, for 90 min, at a pressure of 10 bars of H 2 . After the Be/W and Be/C bilayer deposition by means of thermionic vacuum arc method, annealing in vacuum at 600 °C, for 10 min has been applied to the complex structures. The influence of annealing on the phase composition and atomic intermixing processes in the complex structures has been studied by means of X-ray photoelectron spectroscopy (XPS) and conversion electron Mossbauer spectroscopy (CEMS). The layered structures present an oxidation gradient with oxide phases in the uppermost layers and non-oxidized phases in the lower layers, as observed from the XPS data. The CEMS results revealed that the as-deposited structures contain a main metallic Fe phase and secondary superparamagnetic Fe oxide phases at the Fe/Be interface, while annealed samples present a large contribution of Fe–Be and Fe–C mixtures. The annealing treatment induces considerable atomic interdiffusion, strongly dependent on the nature of the upper layer. In the case of Be/W system, the annealing provides a much rougher Be/W interface, while in case of the Be/C structure, the annealing treatment only homogenize the structure over the whole depth.

Iron doped bismuth selenide (Bi 2 Se 3 :Fe, 5–8 at.%) films were deposited on Si (100) substrates using pulsed laser deposition at different substrate temperatures. The epitaxial films with high c-axis orientation were grown at 400 °C and 450 °C. X-ray photoelectron spectroscopy revealed the presence of oxidized surface layer and Fe–Se bonding with the Fe valence state of + 3. The valence state was proved by Conversion Electron Mossbauer Spectroscopy. These results, along with quantitative element analysis confirmed the substitution of Bi by Fe ions. The Mossbauer spectroscopy showed paramagnetic behavior of the sample grown at 450 °C, whereas the magnetization measurement revealed weak ferromagnetic signal (~ 10 3 A/m), attributed with the oxidized layer. The growth at elevated temperatures resulted in a heavy oxidation of the samples.

A 460 nm thick amorphous SiO2 layer, formed on a Si (100) surface by air-annealing the Si substrate at 1100oC for 24 h, was implanted with 57Fe to a fluence of 1 x 1016/cm2 at room temperature and annealed at temperatures up to 1000oC. The implanted and annealed samples were studied by conversion electron Mossbauer spectroscopy (CEMS) and magnetization measurements. The CEMS spectra up to an annealing temperature of 600oC showed the presence of a singlet due to dispersed Fe ions and paramagnetic doublets with hyperfine parameters characteristic of Fe2+ and Fe3+. The spectrum after the 1000oC annealing was dominated (> 80%) by ferromagnetic sextets, the main components of which were sextets with a hyperfine field of 320(20) kOe and 264(20) kOe, showing the formation of Fe0 clusters, in agreement with previous observations. Magnetization measurements (m(H)) on the sample after the 1000oC annealing showed a small hysteresis at 4 K and saturation magnetization with zero hysteresis at room temperature, reached with application of small external field. The CEMS measurement on this sample was repeated after storing the sample under ambient conditions for a period of 6 months. The spectrum showed complete disappearance of the ferromagnetic sextets and the presence only of paramagnetic doublets due to Fe2+. Evidently progressive oxidation of the Fe clusters had occurred. Magnetization results confirm the paramagnetic transformation of the Fe clusters.

An atomic-scale quantitative analysis of the structural and magnetic properties of surfaces, interfaces and complex nanostructures is of fundamental relevance for the development of new materials for spintronics. Studies of buried magnetic interfaces and depth-resolved measurements in layered magnetic nanostructures are particularly challenging, and the combination of conversion electron Mossbauer spectroscopy and/or nuclear resonant scattering of synchrotron radiation with isotope-enriched probe layers can be a powerful tool in this field. The potential offered by the application of isotope-selective measurements for the study of Fe-based layered magnetic nanostructures is illustrated with our recent results on the investigation of depth-dependent spin structures and interfacial interdiffusion in exchange-biased ferromagnetic/antiferromagnetic bilayer systems and of an epitaxial magnetic system with perpendicular magnetic anisotropy, obtained from samples prepared with ultrathin 57 Fe probe layers placed at different depths during the growth processes, via molecular beam epitaxy or sputtering deposition.

The room temperature 57 Fe Mossbauer and XPS spectra were measured for polycrystalline iron-based Fe–Cr alloys. The spectra were collected using three techniques: the transmission Mossbauer spectroscopy (TMS), the conversion electron Mossbauer spectroscopy (CEMS) and the X-ray photoelectron spectroscopy (XPS). The combination of these experimental techniques allows to determine changes in Cr concentration and the presence of oxygen in bulk, in the 300 nm pre-surface layer and on the surface of the studied alloys.

The effect of thermal annealing on the interface of 57Fe/Ti/Co multilayer and associated changes in microstructure, hyperfine field and bulk magnetic properties such as saturation magnetization, coercivity and squareness has been studied by X-ray diffraction, X-ray reflectivity, conversion electron Mossbauer spectroscopy and vibrating sample magnetometry. With increase in annealing temperature, interdiffusion leads to an increase in the roughness, hyperfine fields and coercivity along with a decrease in saturation magnetization. Annealing at 823 K leads to the formation of a FeCo phase along with the precipitation of Ti. The electrical resistivity (ρ) of the as-deposited sample decreases on annealing and hence the thermal coefficient of resistance (TCR) goes from negative to positive on annealing the samples. All samples show Curie temperature in excess of 723 K.

Effects of annealing temperature on the structural and magnetic properties of Ni 0.8 Zn 0.2 Fe 2 O 4 thin films on Si (100) substrates were investigated at room temperature by X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, a vibrating sample magnetometer and conversion electron Mossbauer spectroscopy. The thin films were prepared by a sol–gel spin-coating technique. It was observed that Ni 0.8 Zn 0.2 Fe 2 O 4 thin films annealed at above 600 °C exhibited a single phase cubic spinel structure, and the lattice constant of ferrite thin films decreased monotonically from 0.8370 to 0.8346 nm. Their coercivity decreased from 14 to 11 kA/m when the average grain size increased from 47 to 172 nm by varying the annealing temperature from 600 to 900 °C, while their saturation magnetization increased from 433 to 544 kA/m. The study of Mossbauer spectroscopy showed that thin films were completely magnetically ordered. The isomer shift and the quadrupole splitting decreased with increasing annealing temperature while the hyperfine field increased. The change in the cation distribution of thin films was also discussed.

The relation between the interface structure and the exchange bias was studied in the epitaxial CoO/Fe(0 0 1) bilayers that were grown on MgO(0 0 1) using molecular beam epitaxy. Three samples with different interface structures were prepared. The CoO/Fe bilayer, which was prepared using the reactive evaporation of CoO, served as the reference sample. In the other two samples, the CoO/Fe interfaces were modified prior to the CoO growth using either (i) the deposition of a 2 A thick Co layer or (ii) an exposure to molecular oxygen, which resulted in under- and over-oxidized CoO/Fe interfaces, respectively. The actual structures of the resulting interfaces were revealed using conversion electron Mossbauer spectroscopy. For each sample, an iron oxide was found at the interface, and its amount depended on the sample preparation recipe. The exchange bias effect (EB), as a function of the temperature, was experimentally studied in detail using VSM magnetometry. The coercivity showed a distinct peak near the blocking temperature for all samples; however, the peak's location and its width were diverse. The obtained EB values depended on the interface structure. The largest hysteresis loop shift (HEB = 180 Oe at 4 K) was obtained for the sample with the thickest interfacial iron oxide layer.

Fe/Cr multilayers were deposited by molecular beam epitaxy on the MgO(1 0 0) substrate. Structural properties of the samples were analyzed by low energy electron diffraction, high resolution transmission electron microscopy (HRTEM), as well as by X-ray reflectivity, conversion electron Mossbauer spectroscopy (CEMS) and Auger electron spectroscopy. Investigations revealed multilayered system built of well-ordered Fe and Cr thin films with (1 0 0) orientation. A high geometrical perfection of the system, i.e. planar form of interfaces and reproducible thickness of layers, was also proven. Fe/Cr interface roughness was determined to be 2–3 atomic layers. CEMS studies allowed to analyze at atomic scale the structure of buried Fe/Cr interfaces, as well as to distinguish origin of interface roughness. Roughnesses resulting from interface corrugations and from the Fe–Cr interdiffusion at interfaces were observed. Fe/Cr multilayers showed strong antiferromagnetic coupling of Fe layers.

Many of the Fe–nitride phases have been studied in much detail. Nevertheless there is still a debate on the most efficient, exact and controlled way of obtaining thin films of the desired iron nitrides phases. We present the recent state of our research focusing on the low and high nitrogen-iron phases and transformations between them due to irradiation, temperature and time exposure. Thin films of iron nitrides were deposited by Molecular Beam Epitaxy in Ultra High Vacuum conditions. We grew films of the FeN alpha (α″-Fe 16 N 2 ), epsilon (e-Fe x N, 2 ⩽ x ⩽ 3) and gamma (FeN y , y > 0.5) phases. By changing the parameters of growth conditions we tried to obtain the α″-phase in its possible purest form. We grew the e-phase mainly in a nonmagnetic form. We worked also on iron mononitride FeN, which is known to exist in different phases. There is a debate on the exact crystal structure and the coexistence of these phases. On the basis of room temperature Conversion Electron Mossbauer Spectroscopy analysis accompanied with Rutherford Backscatering Spectroscopy spectra we show our results on the growth and transformations of the samples under different conditions.

In order to study specific phenomena at ferromagnetic/semiconducting interfaces, of potentially high interest in spintronics and information technology, structural aspects and magnetic properties of Fe thin films grown on Si(0 0 1) substrates by RF sputtering have been investigated using 57 Fe conversion electron Mossbauer spectroscopy (CEMS) and magneto-optic Keer effect (MOKE). Films of different thicknesses have been deposited either directly on crystalline Si substrates or on Cu buffer layers. An inherent Fe oxide layer is observed in all as prepared films, with a relative thickness decreasing drastically with the deposition time. The Cu buffer layer does not diminish either the interfacial diffusion or the oxidation process. An efficient method to prepare sharper oxygen- and silicon-free interfaces for an improved spin injection, via thermal treatment in hydrogen atmosphere, is proposed. Accordingly, the hydrogenation treatments are very efficient in the modification of the ferromagnetic film structure, phase composition, magnetic properties and interfacial mixing.

Iron single crystals were implanted with nitrogen at room temperature, with a fluence of 5×10 17 cm −2 and 50 keV energy, to produce iron nitride phases and characterize the influence of the crystal orientation. The stability and evolution of the nitride phases and diffusion of implanted nitrogen were studied as a function of successive annealing treatments at 250 °C in vacuum. The composition, structure and magnetic properties were characterized using RBS/channeling, X-Ray Diffraction, Magnetic Force Microscopy, Magneto-optical Kerr Effect and Conversion Electron Mossbauer Spectroscopy. In the as-implanted state the formation of Fe 2 N phase was clearly identified in all single crystals. This phase is not stable at 250 °C and annealing at this temperature promotes the formation of ɛ - Fe 3 N , or γ ′ - Fe 4 N , depending on the orientation of the substrate.

The production and characterization of ultra-thin iron oxide films grown on an atomically clean Ag(100) surface by molecular beam epitaxy (MBE) is presented. The goal of this work was to prepare ultra-thin FeO(100) with excellent crystallographic quality. The films were prepared with high purity 57 Fe and O 2 and afterwards analyzed in situ by means of Low Energy Electron Diffraction (LEED), X-Ray Photoelectron Spectroscopy (XPS) and Conversion Electron Mossbauer Spectroscopy (CEMS). During preparation the evaporation rate, the O 2 partial pressure, film thickness and annealing procedures were varied. The analysis of the various samples showed that in general a mixture of FeO and Fe 3 O 4 phases is obtained. We determined the best conditions to produce the desired oxide (FeO). Besides the paramagnetic phase, the antiferromagnetic phase of the FeO films was characterized by low temperature Mossbauer spectra.

The adsorption of oxygen on a pseudomorphic iron monolayer deposited on a W(110) surface was studied experimentally and theoretically. Standard surface characterization methods, such as Auger electron spectroscopy and low energy electron diffraction, and specific nuclear methods, such as conversion electron Mössbauer spectroscopy (CEMS) and nuclear resonant scattering of synchrotron radiation, combined with theoretical calculations based on the density functional theory allowed us to determine the structure of the oxygen adsorbate and the electronic properties of iron atoms with different oxygen coordinations. The oxygen-(3×2) structure on the iron monolayer was recognized and was interpreted to be a state with oxygen chemisorbed on the non-reconstructed surface with modest electron transfer from iron to oxygen. A transition from chemisorbed oxygen to the onset of Fe-oxidation is revealed by distinct changes in the CEMS spectra.

The effect of swift heavy ion irradiation in novel electrodeposited ternary amorphous alloys was studied by 57 Fe and 119 Sn conversion electron Mossbauer spectroscopy. Irradiation of Sn3Co3Fe with 246 MeV Kr ions induces partial segregation and rearrangement of the constituent elements from the amorphous state toward an ordered state. The Sn3Ni3Fe irradiated with 600 MeV Xe ions exhibits transformation from the as-deposited amorphous toward a slightly more disordered state due to the swift heavy ion irradiation.

Effect of interfacial roughness on magnetoresistance (MR) value in Fe/Cr multilayers was studied. The Fe/Cr multilayers were prepared on a MgO(100) substrate by molecular beam deposition technique and doped with Bi and In surfactants. The morphology of the layers, especially the interface structure, was studied using conversion electron Mossbauer spectroscopy (CEMS). CEMS spectra indicate an increase in the width of interfaces of modified samples; this effect is stronger for the sample doped with In. Auger electron spectroscopy shows the segregation of the surfactant to the surface. Magnetic and magnetotransport properties of the samples were studied by the magneto-optic Kerr effect and MR measurements. The observed hysteresis loops confirm in all samples antiferromagnetic arrangement of Fe layers sandwiched between Cr while the value of MR is larger for the doped samples. It was observed that roughening of the interfaces resulted in an increase of the MR effect.

Novel Sn–Ni–Fe ternary phases, which never occur in the metallurgical alloys, were successfully prepared by deposition from an electrolyte based on sodium gluconate, using DC electrodeposition conditions. 57 Fe and 119 Sn conversion electron Mossbauer spectroscopy and PXRD investigations of these alloys showed that they are amorphous and dominantly ferromagnetic. The occurrence of amorphous Sn–Fe–Ni ternary alloy phase in deposits was found to increase with the current density applied during the deposition. The co-deposition kinetics is mainly governed by the electrodeposition behavior of the tin–gluconate complex that forms in the electrolyte. The high cathodic polarization due to the tin–gluconate discharge causes an apparent mass transfer coupled co-deposition of iron. The nickel deposition rate is independent of the potential and of the partial current of the co-depositing species.

Fe–Pd-based ferromagnetic shape memory alloys are based on metastable random solid solutions in the austenite and martensite phases, which require preparation from the equilibrium γ phase by rapid cooling. Employing splats, we explore the impact of annealing treatment on the disordered solid solution, phase formation and lattice defects using a combined conversion electron Mossbauer spectroscopy – X-ray diffraction study. We discuss indications of short range ordering tendencies as well as the impact of splat microstructure and defects on phase formation.

The magneto-optical Kerr effect (MOKE) completed by other surface sensitive methods as integral low-energy and conversion electron Mossbauer spectroscopy, scanning and transmission electron microscopy and by X-ray diffraction have been used with the aim to trace the surface microstructure and magnetic properties of FeSiB amorphous ribbons prepared by planar flow casting. The general composition of studied samples is Fe80SixB20−x, where x=4, 6, 8, 10 at.%. It is shown that MOKE used for magnetization, hysteresis loop, and domain structure determination is highly beneficial in a detection of both surface crystallization and local ordering of atoms into magnetically different clusters of amorphous structure. Moreover, a combination of blue and red laser with different penetration depths yields unique results concerning the surface anisotropy and depth sensitivity. In the case of samples with 4, 6, and 8 at.% Si MOKE detects two magnetically different phases diverging in coercivity values H c , however, not varying with the sample composition. These phases have been identified by Mossbauer measurements as FeSi and FeB clusters. Their relationship changes with Si concentration. On the other hand, a strong increase in the surface H c found for the sample with 10 at.% Si has indicated a nanocrystallization. It was confirmed by electron microscopy, Mossbauer and X-ray diffraction results. The size of nanocrystals has varied between 200 nm and 500 nm.

Structural and magnetic properties of exchange spring magnets consisting of hard magnetic (FePt) and soft magnetic (Fe and Co) bilayers, prepared by ion beam sputtering method are studied via X-ray diffraction (XRD), magneto-optic Kerr effect (MOKE) and vibrating sample magnetometry (VSM). Thin tracer layers of 57 Fe were introduced in the soft layer in order to observe the Fe spin structure and interfacial diffusion by Conversion Electron Mossbauer Spectroscopy (CEMS). The observed in-plane exchange spring behavior extends also to the magnetic hard layer, whose switching field can be tuned in an unexpected manner via the top soft magnetic layer. To explain the observed phenomenon it is suggested that the increased switching field, found in the system with a Co/Fe bilayer acting as a single soft magnetic layer, is compatible with a peculiar behavior of the stiffness coefficient of the heterogeneous soft magnetic layer. According to this observation, possibilities to maximize the exchange spring effects via suitably chosen non-homogeneous soft magnetic layers are open.

Structural aspects and atomic intermixing processes in Be/W bilayers deposited on Si(0 0 1) substrates with Fe buffer layers enriched in the 57 Fe Mossbauer isotope have been studied via atomic force microscopy, grazing incidence X-ray diffractometry, X-ray reflectometry, X-ray photoelectron spectroscopy and conversion electron Mossbauer spectroscopy. The mentioned investigations allowed a full sequential characterization of the involved interfaces. Various ionic configurations appeared for Fe or W, while an amorphous state was observed in the case of Be. It has been proven that the Be layer has a negative influence on the roughness of the whole structure, which however presents an oxidation gradient from more oxidized elements at the surface towards more reduced elements in deeper layers. A strong diffusion of the W atoms inside the Be layer, induced by the deposition method, as well as of the Fe atoms inside the Be layer, induced by thermal annealing, has been evidenced.

Thin magnetic films were synthesized by means of implantation of iron ions into single-crystalline (1 0 0) substrates of strontium titanate. Depth-selective conversion electron Mossbauer spectroscopy (DCEMS) indicates that origin of the samples magnetism is α-Fe nanoparticles. Iron-substituted strontium titanate was also identified but with paramagnetic behaviour at room temperature. Surface magneto-optical Kerr effect (SMOKE) confirms that the films reveal superparamagnetism (the low-fluence sample) or ferromagnetism (the high-fluence sample), and demonstrate absence of magnetic in-plane anisotropy. These findings highlight iron implanted strontium titanate as a promising candidate for composite multiferroic material and also for gas sensing applications.

Conversion-electron Moessbauer spectroscopy analysis of iron surface states in the dense ceramic membranes made of {sup 57}Fe-enriched SrFe{sub 0.7}Al{sub 0.3}O{sub 3-{delta}} perovskite, shows no traces of reductive decomposition or carbide formation in the interfacial layers after operation under air/CH{sub 4} gradient at 1173 K, within the limits of experimental uncertainty. The predominant trivalent state of iron cations at the membrane permeate-side surface exposed to flowing dry methane provides evidence of the kinetic stabilization mechanism, which is only possible due to slow oxygen-exchange kinetics and enables long-term operation of the ferrite-based ceramic reactors for natural gas conversion. At the membrane feed-side surface exposed to air, the fractions of Fe{sup 4+} and Fe{sup 3+} are close to those in the powder equilibrated at atmospheric oxygen pressure, suggesting that the exchange limitations to oxygen transport are essentially localized at the partially reduced surface. - Graphical Abstract: Conversion-electron Moessbauer spectroscopy analysis of dense ceramic membranes made of {sup 57}Fe-enriched SrFe{sub 0.7}Al{sub 0.3}O{sub 3-{delta}} perovskite, shows no reductive decomposition in thin interfacial layers after testing under air/CH{sub 4} gradient, enabling stable operation of the ferrite-based ceramic reactors for partial oxidation of methane. Highlights: > Conversion-electron Moessbauer spectroscopy is used for mixed-conducting membranes. > No decompositionmore » is detected in the membrane surface layers under air/CH{sub 4} gradient. > Due to kinetic stabilization, Fe{sup 3+} states prevail at the surface exposed to methane. > Transmission Moessbauer spectra show perovskite decomposition on equlibration in CH{sub 4}. > Ferrite-based ceramic reactors can stably operate under air/CH{sub 4} gradient.« less

The electronic and magnetic properties of epitaxial Fe 3 O 4 (001) films on MgO(100) substrates were studied throughout the 2.5- to 30-nm thickness range using conversion electron Mossbauer spectroscopy. Despite the superparamagnetism that was observed for film thickness below 5 nm, the Verwey transition persisted even for the thinnest film. Temperature-dependent Mossbauer measurements between 80 K and 400 K revealed that the activation energy for the magnetic moment fluctuations in the 3-nm magnetite film is higher than the magnetic anisotropy energy by an order of magnitude.

In this work, we present a detailed analysis of the microstructure and magnetic properties of 50 ± 2 nm thick polycrystalline Fe100−xGax (10 ≤ x ≤ 35) films. Two sets of Fe100−xGax films were fabricated on Si 1 0 0 substrates with and without a forming field Hf present. Microstructural properties were studied using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and conversion electron Mossbauer spectroscopy (CEMS). Magnetic properties were studied using the magneto optical Kerr effect (MOKE) magnetometer. For all films, the 1 1 0 texture normal to the film plane was observed from XRD. No peaks corresponding to the ordered D03 or L12 phases were observed from XRD. Using CEMS, the disordered A2 phase was confirmed in all films. It was found that the magnetostriction in Set-1 (forming field Hf = 0) films was ∼40–50% higher compared to the Set-2 (Hf ≠ 0) films over the whole Ga composition range studied. Both film sets have a strong dependence of saturation field Hs on Ga composition. Set-1 films were magnetically isotropic but a weak uniaxial anisotropy was observed in Set-2 films. The saturation field Hs in Set-2 films was significantly lower compared to the Set-1 films. It was concluded that the Hf reduced Hs but also reduced effective saturation magnetostriction constant λeff in the films.

57 Fe conversion electron Mossbauer spectroscopy, XRD and AFM measurements were used to study the radiation effect of 246 MeV Kr, 470 MeV Xe and 710 MeV Bi ions on electrochemically deposited iron thin films. It was found that, in the irradiated electrochemically deposited crystalline ferromagnetic α-Fe coatings, partial amorphisation of Fe took place. The relative amount of the ferromagnetic amorphous phase increased with both ion energy and ion mass as well as with the fluence of irradiation.