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The paper reports on a comparative study of local Fe states, phase composition and magnetoresistivity of granular nanocomposite films FeCoZr–CaF 2 sintered in pure Ar and Ar + O sputtering atmosphere. For the first time peculiarities of temperature and magnetic field dependencies of magnetoresistance are analyzed with respect to partial oxidation of nanoparticles and perpendicular magnetic shape anisotropy.

X-ray diffraction (XRD) and Mossbauer spectroscopy techniques combined with theoretical calculations based on the Korringa-Kohn-Rostoker (KKR) electronic structure calculation method were used to investigate σ-phase Fe100−xRex alloys (x = 43, 45, 47, 49 and 53). Structural data such as site occupancies and lattice constants were derived from the XRD patters, while the average isomer shift and distribution curves of the quadrupole splitting were obtained from the Mossbauer spectra. Fe-site charge-densities and the quadrupole splittings were computed with the KKR method for each lattice site. The calculated quantities combined with the experimentally determined site occupancies were successfully used to decompose the measured Mossbauer spectra into five components corresponding to the five sublattices.

We report on the results of X-ray absorption near edge structure (XANES) studies at the Mn:L2,3, Ru:K and O:K edges of novel manganites, Sr2Mn0.5Ru0.5O4 and Sr3MnRuO7. Measurements were carried out on polycrystalline powder samples at room temperature. From the analysis of the XANES spectra the average manganese valences of 3.4 in bilayer Sr3MnRuO7 and 3.1 in single layer Sr2Mn0.5Ru0.5O4 are obtained. The corresponding average valences for Ru ions are 4.6 and 4.9, respectively. This indicates that Ru doping gives rise to a decrease of Mn valence, whereas Ru valence increases, compared to Mn(IV) and Ru(IV) in undoped compounds. The effect of charge disproportionation is stronger in the single layered compound than in the bilayered one. © 2007 Elsevier B.V. All rights reserved.

Using the new technique of nuclear forward scattering (NFS) of synchrotron radiation, we studied the magnetic hyperfine fields B hf and ordering temperatures T M of the Laves phases LuFe 2 (cubic C15) and ScFe 2 (hexagonal C14) at pressures up to 90 GPa and temperatures up to 700 K. For LuFe 2 we find for T M first an increase from 562 K at 0 GPa to 603 K at 10 GPa and then a decrease to 295 K around 75 GPa. The hyperfine fields B hf show at 295 K a continuous decrease with pressure, indicating a reduction of the Fe band moment. A similar behaviour of both T M and B hf was observed in ScFe 2.

The relation between nanoscale structure, local atomic order and magnetic properties of (FeCoZr)(x)(CaF2)(100-x) (29 LT = x LT = 73 at. %) granular films is studied as a function of metal/insulator fraction ratio. The films of a thickness of 1-6 mu m were deposited on Al-foils and glass-ceramic substrates, by ion sputtering of targets of different metal/insulator contents. Structural characterization with X-ray and electron diffraction as well as transmission electron microscopy revealed that the films are composed of isolated nanocrystalline bcc alpha-FeCo(Zr) alloy and insulating fcc CaF2 matrix. They grow in a columnar structure, where elongated metallic nanograins are arranged on top of each other within the columns almost normal to the substrate surface. Mossbauer spectroscopy and magnetometry results indicate that their easy magnetization axes are oriented at an angle of 65 degrees-74 degrees to the surface in films with x between 46 and 74, above the electrical percolation threshold, which is attributed to the growth-induced shape anisotropy. Interatomic distances characteristic for metallic state of alpha-FeCo(Zr) nanograins were revealed by X-ray Absorption Spectroscopy. The results show a lack of surface oxidation of the alloy nanograins, so the growth-induced orientation of nanograins in the films cannot be attributed to this effect. The study is among the first to report a growth-induced non-planar magnetic anisotropy in metal/insulator granular films above the percolation threshold and to reveal the origin of it. (C) 2014 AIP Publishing LLC.

The results of neutron diffraction investigations of TbMn2D2 deuteride are presented and analysed. The location of deuterium atoms in the lattice was determined. Magnetic ordering in this compound appears below 300 K. The magnetic structure can be described by the propagation vector [ 1 1 1 ]. The Tb sublattice couples antiferromagnetically, with magnetic moments equal to 4.8 µB, and the Mn sublattice is also coupled antiferromagnetically, with different magnetic moments.

A 169 Tm and 57 Fe Mossbauer study was performed on the intermetallic compound Tm2Fe3Si5. The magnetic behaviour below T=20 K is well described by a relaxation model.

Deoxygenated Y 1- x Ca x Ba 2[ Cu 0.99257 Fe 0.008]3 O 6.1 compounds with calcium content of x =0.05, 0.08, 0.12, 0.16, 0.2, 0.26 were prepared by the standard ceramic method. The system exhibit insulator to metal transition. The onset of superconductivity is detected in the sample with x =0.26. The influence of doped holes on low temperature antiferromagnetic order has been investigated. Low temperature Mössbauer spectra consist of two sextets with relative ratio changing with hole concentration. The sextets are broadened, their shape and temperature dependence indicate the existence of magnetic order fluctuations with the relaxation time slightly higher than the observation time of the method ~10-7 s .

Neutron scattering and AC susceptibility measurements have been made on isotopically enriched 154 SmMn 2 ( Ge 0.9 Si 0.1 ) 2 . A temperature versus pressure magnetic phase diagram is proposed. The incommensurate cone structures detected in SmMn2Ge2 at low temperatures and pressures do not appear in the phase diagram of the Si-substituted system. There is no evidence of a change in the magnetic structure associated with a small peak in susceptibility observed at around 145 K which has previously been interpreted in terms of changes to the cone structure. However, as with SmMn2Ge2, the non-collinear magnetic structures of these magnetic phases are such that a larger antiferromagnetic component appears within (0 0 1) ab -planes in the ferromagnetic states than in the antiferromagnetic state. With increasing Si substitution, the antiferromagnetic phase becomes the magnetic equilibrium state over a wider temperature range. The observed changes in the Mn–Mn spacing and magnetic coupling are largely consistent with previous related observations, although under a pressure of ∼8 kbar, low-temperature magnetic structures are found below the critical lattice spacing of a =4.031 A which are similar to those observed at ambient pressure.

Using Mossbauer Spectroscopy the kinetics of the σ-phase formation was studied in situ on Ti-doped quasi-equiatomic Fe–Cr alloys having an average grain size equal to 31(2) μm. The kinetics was studied both with a traditional approach i.e. the amount of the σ-phase precipitated, A σ , was determined from the spectral area, as well as with a novel approach i.e. in terms of the average isomer shift. In both cases the data could be well fitted in terms of the Johnson–Avrami–Mehl equation which yielded the kinetics parameters: the time constant, k , and the form factor, n . Assuming the k -values follow the Arrhenius law, the Ti-induced change in the activation energy, E , was determined. In particular, it was revealed that addition of 1.5 at% Ti or less accelerates the transformation, with the highest rate for 0.3 at% Ti, and the difference in E equals to 18.8 kJ/mol. In alloys with Ti-content higher than 1.5 at%, the formation of the σ-phase was retarded. The value of E =207±20 kJ/mol was found for the Fe 53.8 Cr 46.2 alloy.

The nuclear forward scattering (NFS) of synchrotron radiation is especially suited for probing magnetism at very high pressure, here in the Mbar range, by the nuclear resonances of 57Fe and 151Eu. We report on high pressure (h.p.) NFS studies with the 14.4 keV transition of 57Fe on magnetic RFe2 Laves phases of cubic C15 structure (YFe2, GdFe2) and hexagonal C14 structure (ScFe2, TiFe2) at pressures up to 100 GPa (=1 Mbar). We present also h.p. NFS studies performed with the 21.5 keV resonance of 151Eu, probing the magnetism in the CsCl-type h.p. phase of EuTe.

X-ray and neutron diffraction measurements confirm that (R = Tb, Dy and Ho) compounds show the tetragonal type of crystal structure. Magnetization and magnetic susceptibility data indicate antiferromagnetic behaviour below the N?el temperatures at 8.5 K in and 3.35 K in . A metamagnetic transition at kOe and T = 4.2 K has been detected in . The other two compounds give at 4.2 K magnetization curves characteristic for paramagnetic materials up to H = 50 kOe. The magnitudes of magnetic moments at H = 50 kOe are smaller than the free ion values for all three compounds. and exhibit at 1.5 K modulated antiferromagnetic order described by two component wavevectors . The magnetic moments are localized on the lanthanide ions and amount at 1.5 K to 7.68(11) and 7.3(3) in and respectively. Diffuse magnetic peaks observed at 1.5 K in the neutron diffraction pattern of indicate that a long-range antiferromagnetic order starts to set up at this temperature.

The $^{55}\mathrm{Mn}$ NMR spin-echo spectra for the cubic $\mathrm{Gd}{\mathrm{Mn}}_{2}{\mathrm{H}}_{x}$ compounds with $x=0, 0.5, 1, 2, 2.5, 3, 3.4, 3.5$ and for the rhombohedral Gd${\mathrm{Mn}}_{2}$${\mathrm{H}}_{4.3}$ are reported. For the samples with $x=0, 0.5, \mathrm{and} 1$ spectra with a single broad line at 129, 132, and 135 MHz, respectively are observed. Satellite patterns with up to three lines are observed for $2lxl3.5$. The effect is attributed to a diversification of manganese moments caused by hydrogen neighbors leading to up to three values of the Mn moment in the cubic hydrides with $xg2.5$. For Gd${\mathrm{Mn}}_{2}$${\mathrm{H}}_{3.5}$ the directions of Mn magnetic moments with respect to the magnetization are derived from the line shifts in an applied magnetic field. The two narrow lines observed for the rhombohedral compound Gd${\mathrm{Mn}}_{2}$${\mathrm{H}}_{4.3}$ at 186 and 423 MHz are attributed to the two Mn sites in the structure. The observed effects are explained by the presence of four different magnetic structures and four manganese spin states in the series.

For the hexagonal phase FeMnP 1- x As x , neutron diffraction and Mossbauer spectroscopy results are compared. The magnetoelastic transition is accompanied by a drastic change in the 57 Fe hyperfine field that is more than twice as large in the ferro (F) than in the antiferromagnetic (AF) state. Such trends exist in FeMnX (X = As, P) and can be related to the changes in the FeFe distances.

Magnetic order in ultrathin Fe(110) films in a Cr(110) matrix and its temperature dependence were analyzed using conversion electron Mossbauer spectroscopy (CEMS). The samples were characterized by flat interfaces, as tested by SPA-LEED (spot profile analysis LEED). Fe films consisting of D atomic layers with 1 ≤ D ≤ 31 were doped by 57 Fe probes and analyzed using CEMS in situ in UHV, for 100 K ≤ T ≤ 450 K. All spectra could be fitted by Zeeman sextets with B hf ( T ) following Bloch laws. For films with 2 ≤ D ≤ 6, the first Fe layer in the CrFe interface shows a reduced ground state hyperfine field of B s (0) = 25.8 T, which differs from values determined previously for rough interfaces. It agrees roughly with the predictions from an alloy model. Spin-wave parameters are reduced in comparison with samples W(110)/Fe/Ag. For thicker films ( D > 6), two subcomponents of the interface can be distinguished, with equal abundance, but different hyperfine fields and different b parameters; apparently they belong to two magnetically inequivalent states resulting from the antiferromagnetic order in Cr. Extraordinary low values for the surface enhancement of the b parameters, α s, a = 1.5 and α s, b = 1.1, respectively, and a large value of 10 atomic distances for the interaction length are explained by the antiferromagnetic order of the matrix. The low values for the surface enhancement of the spin-wave parameters differ strongly from results reported for the case of rough interfaces. For the double layer, a break of B hf ( T ) was observed near the Neel temperature of Cr. Parameters of the monolayer could be roughly determined.

Powder samples of cubic HoMn2Hx (0 ≤ x ≤ 4.3) are characterized by powder XRD and AC/DC magnetometry as a function of temperature and external magnetic field.

The spin echo nuclear magnetic resonance spectra of Y 2 Co 17 A x (A≡N, C, H) are presented. On the basis of the satellite pattern of the 89 Y spectra, we have deduced that N and C atoms occupy the 9e sites (rhombohedral compounds) or 6h sites (hexagonal compounds) around the yttrium site. A decrease in the hyperfine fields at the yttrium and cobalt sites caused by neighbouring interstitial atoms is observed, with a magnitude dependent on the site and the type of interstitial atom. The effect is discussed in terms of the influence of N, C and H atoms on the local electronic structure at the yttrium and cobalt sites and compared with the effect observed in the RE 2 Fe 17 -based compounds (RE, rare earth).

The NMR spin ccho measurements at 4.2 K for YMn2Hx (x=1, 2, 3) compounds are reported. The obtained values of55Mn hyperfine fields are analysed in dependence on the by hydrogen atoms and flips of neighbouring manganese moments. The strong increase of hyperfine field with increasing number of the nearest hydrogen atoms is explained by the change of orbital contribution to hyperfine field.

Temperature and magnetic field dependences of electrical conductivity are systematically studied in granular films (Fe45Co45Zr10) x (Al2O3)100−x (28 ⩽ x ⩽ 64) containing crystalline metallic α-FeCo-based nanoalloy cores encapsulated in an amorphous oxide shell embedded in an amorphous Al2O3 matrix. Formation of ‘metallic core–oxide shell’ nanogranules is confirmed by transmission electron microscopy (TEM) and HRTEM. The structure of core and shell is governed with the difference in the oxidation states of Fe and Co ions investigated with EXAFS, XANES and Mössbauer spectroscopy. A considerable negative magnetoresistance (MR) effect of spin-dependent nature is observed in the whole range of x values. Its increase with decreasing temperature is correlated with the magnetic saturation of superparamagnetic metallic nanogranules. The enhanced MR effect in ‘core–shell’ granular films is related to the percolation of oxide shells and their influence through spin filtering processes. A considerable high field MR at low temperatures and the resulting deviation of MR and squared magnetization are attributed to a magnetic randomness and/or strong magnetic anisotropy of the magnetic oxide shell.

Thermal deposition (TD) and pulsed laser deposition (PLD) techniques were used to prepare GaAs∕Fe(001) crystalline ultrathin films. The magnetic environment of Fe at the Fe∕GaAs(001) interface was investigated by means of conversion electron Mossbauer spectroscopy using an Fe57 probe layer having the equivalent thickness of two atomic layers. The magnetic anisotropies were measured using ferromagnetic resonance. PLD samples were affected by an appreciably higher degree of interface alloying compared with the TD films. The interface in-plane fourfold (cubic) anisotropy is significantly increased and the in-plane interface uniaxial anisotropy is significantly decreased in the PLD samples compared to those prepared using TD. The effective perpendicular demagnetizing field in the PLD films is significantly decreased compared to the TD samples due to an unexpected increase in the interface uniaxial perpendicular anisotropy at the Fe∕Au(001) interface.

Fe ∕ Mg O ∕ Fe ∕ Cr ∕ Fe tunneling structures were epitaxially grown directly on GaAs(001) without buffer layer. Interdiffusion in the Fe ∕ Ga As interface was investigated using conversion electron Mossbauer spectroscopy. An independent magnetization switching in the Fe electrodes was achieved by pinning the magnetization of the Fe-top electrode by antiferromagnetic coupling across a Cr spacer to another Fe film. For transport measurements, optical lithography and ion etching were applied to reduce the junction area. A tunneling magnetoresistance of 10%–12% at room temperature was found.

We show by CEMS that spin-wave parameters in smooth Fe/Cr(110)-interfaces are reduced below the RADO value b s = 2 b bulk . Two interface states are observed with different values of b s , and of B hf (0) (25 T and 29 T, respectively). This is explained from the antiferromagnetic order of the Cr matrix.

The authors present measurements of the Mossbauer effect for two specimens of the magnetic superconductor Y9Co7 doped with 57Co and 119Sn. The shape and asymmetry of the observed quadrupole spectra were ascribed to the individual features of the three non-equivalent cobalt positions in the Y9Co7 structure. Below the Curie temperature an apparent broadening of the spectra was observed which persists into the superconducting state.

The tetragonal TmCu 2 Si 2 compound is the only magnetically ordered material of the RECu 2 Si 2 group for which crystal field parameters were determined. Quadrupole splitting measured by means of Mossbauer spectroscopy showed that two lowest lying states are nonmagnetic singlets. Therefore, this material is likely to have an induced magnetic moment, mainly due to mixing of the two lowest states. We performed specific heat and magnetic susceptibility measurements of Tm 1− x Lu x Cu 2 Si 2 ( x = 0, 0.025, 0.050, 0.10, 0.25, 0.50 and 1) alloys to determine the crystal field level scheme and compare it with the Mossbauer data. The saturation magnetization of the antiferromagnetic phase was calculated to be 3.2 μ B and the moment is directed along the tetragonal c axis. No direct experimental evidence is known to support this prediction.

The ferrimagnetic compound Er6Mn23 and its hydride Er6Mn23H21 have been investigated using the 166Er and 57Fe (as dilute impurity) Mossbauer resonances. For the hydride a small 57Fe magnetic hyperfine field is observed below 85 K indicating magnetic ordering. This observation is contrary to the previous assumption that the Mn sublattice must be non-magnetic. The 166Er results demonstrate that the Er3+ magnetic moment is not “quenched” by crystal electric fields on hydrogenation.

The x-ray and Mossbauer measurements of both57Fe and161Dy in Dy2Fe17−y Al (y=0, 1,5 and 3) compounds and their hydrides are reported.

The polycrystalline samples of Er2Fe17−xMnx compounds have been studied by57Fe Mossbauer spectroscopy in the temperature range between 4.2K and 200K. A reorientation of the easy axis of magnetization has been evidenced for compound with x=4 in the measurements on magnetically oriented powdered sample. Spin reorientation from the c-axis to the basal plane is observed when temperature is increased above 105K.

The intermetallic compound, YMn12, doped with 0.5at.%57Fe has been investigated using the57Fe Mossbauer resonance. The data show that the Fe impurities occupy preferentially the f-site at the expense of the i- and j-sites. Whereas the i- and j-sites are expected to carry identical local magnetic moments in the ordered state, low temperature hyperfine fields of 50.08(±0.05)T and 2.90(±0.03)T are measured for the i- and j-sites respectively. It is proposed that large transferred hyperfine fields are responsible for this disparity.

The Mossbauer measurements of both57Fe and161Dy in Dy12Fe82B6 system are reported. The presence of B exceeds the magnetic hyperfine fields at both57Fe and161Dy nuclei as compared to corresponding pure metals Fe and Dy respectively. The only small excess of the hyperfine field at57Fe nucleus is observed. The excess at161Dy nucleus is about 12% of the free ion Dy3+ value.

The ferrimagnetic compound Y6Mn23 and its hydride Y6Mn23H26, both doped with 0.5%57Fe, have been investigated using the 57Fe Mossbauer resonance and dc field magnetization measurements. For the hydride a small 57Fe magnetic hyperfine field is observed to increase abruptly below 110 K whereas the bulk magnetization results suggest antiferromagnetic ordering at TN≈ 180 K.

The magnetically ordered DyxFey intermetallic compounds exhibit an excess of the magnetic hyperfine field at the 161Dy nuclei as compared with the free-ion value. The excess is relatively constant across the series. On the other side the saturated iron magnetic moments in the DyxFey (or other heavy rare earth-iron) compounds are reduced as compared with the pure iron metal value. The moments decrease almost linearly with x/y. The possible mechanisms which can originate the excess and the moment reduction are discussed. The role of the 5d electron is considered.

New169Tm Mossbauer and specific heat data recorded for TmCu2Si2 and Tm1/2Lu1/2Cu2Si2 in the temperature range 1.4K to 20K verify that TmCu2Si2 orders magnetically at TN=3K and support earlier conjecture that TmCu2Si2 behaves as a 2-singlet system at low temperatures. However attempts to describe the available data in terms of a single set of parameters suggest that the single-ion and molecular field approximations are an oversimplification of the true situation.

The influence of temperature and time of annealing on hyperfine fields and isomer shifts has been studied for a range of Fe–Cr alloys containing 1–45 at% Cr. It has been revealed that up to 15at% Cr neither time nor temperature of annealing practically does affect the hyperfine parameters. For more concentrated samples, however, both temperature and time of annealing are important. In particular, the Mossbauer spectrum of Fe–45.5 at% Cr annealed at 700°C for 5 h was a single-line indicating that the sample was paramagnetic. The observed changes of the hyperfine fields and the isomer shifts have been interpreted in terms of a spin and charge trasfer, respectively. Strong linear correlations between the following quantities have been revealed: the hyperfine field H (0,0) and the isomer shift IS(0,0); the average hyperfine field H and the average isomer shift IS ; the average hyperfine field H and the average number of Cr atoms in the first two coordination spheres, N . It has been calculated from the first two correlations that a) a change of polarization of itinerant s-like electrons of one electron is equivalent to a change of the hyperfine field of 1602 kOe, and b) on average, a unit change of s-like electron polarization is equivalent to 3277 kOe. The two constant are very close to theoretical estimations, which can be found in literature. Correlation between the hyperfine field and the isomer shift led to a conclusion that the substitution of Fe atoms by Cr ones decreases the density of spin-up electrons on average by 0.026 electrons per one Cr atom in a unit cell. These electrons are most likely trapped by Cr atoms, because the hyperfine field at neighbouring Fe nuclei decreases and the density of charge at those nuclei increases at the rate of 0.029 electrons per one Cr atom in a unit cell. Based on the results obtained, a formula describing the dependence of the average hyperfine field on Cr contents and on the heat treatment has been postulated for Fe–Cr alloys.

The compounds Dy 2 Fe 17− y Co y (O⩽ y ⩽17) have been investigated using the Mossbauer resonances at the 161 Dy and 57 Fe nuclei (at 4.2 K). The changes of the hyperfine interaction parameters have been determined as a function of the Co content. The dependence of the hyperfine field at the 57 Fe nuclei on y is quite different from that for the 161 Dy nuclei. The 5d electron model is proposed to explain this behaviour.

The hyperfine interaction parameters at the 161Dy and 57Fe nuclei in Dy2−yYyFe17 compounds (0⩽y⩽2) have been determined from the Mossbauer effect measurements at 4.2 K. The dysprosium atoms are substituted by the yttrium atoms across the series and then the 5d electrons of Dy are replaced by the 4d electrons of Y. The hyperfine interaction parameters for both nuclei remain constant versus Y content. The full equivalency between 5d and 4d electrons has been deduced. The excess of the hyperfine magnetic field at the 161Dy nuclei and the reduction of the magnetic hyperfine field at the 57Fe nuclei can be explained as a result of the presence of the magnetically polarized 5d (or 4d) electrons in these compounds.

The R6(Fe1−yMny)23Hx compounds (R=rare earth,Y) are especially interesting for two reasons: (1) x=O.The high magnetic ordering temperatures observed for the boundary phases of the host materials plunge dramatically in the intermediate composition region1 (for example see Table 1). (2) x≠O.The effect of loading with hydrogen varies wildly2–4. It can result in either suppression or enhancement of the magnetic order, or alteration of the magnetic structure itself.

According to our previous report, a heat treatment may affect hyperfine parameters in Fe-Cr /1/. The aim of the present investigation was to study this problem in detail. Towards this end measurements on a range of Fe-Cr samples containing 1 – 45 at % Cr were carried out using the Mossbauer spectroscopy. The samples were subject to different heat treatment in terms of different temperature (300-900°C) and time · (1–150 hours) of annealing.