Search

RE 1 Ba 2 Cu 3 O 7-δ (RE = Er or Y) superconducting films were fabricated by reactive laser deposition, in situ, on YSZ(100), SrTiO 3 (100) and Si(001), under various conditions. A complete XRD investigation showed that the films grown with high substrate temperatures (T s > 740°C) combined with low fluences (1.5 J / cm 2 < 2 J / cm 2 ) and laser repetition rate (4 Hz) have the best structural characteristics, very good electrical and magnetic properties.

Structural information on ultrathin films of Fe x Co 1− x alloys grown epitaxially by coevaporation on Si(0 0 1) at room temperature is obtained by X-ray photoelectron diffraction, low-energy electron diffraction, inelastic medium-energy electron diffraction and transmission electron microscopy. The body-centered-cubic structure is found to be stabilized for alloy thin films up to very high concentration of Co beyond the thermodynamically stable bcc range (0.25⩽ x ⩽1). For alloy films with thickness up to 10 monolayers, the bcc structure with (0 0 1)[1 0 0]Fe x Co 1− x //(0 0 1)[1 0 0]Si is actually observed over the entire range of alloy concentrations that includes elemental bcc Co. All films are ferromagnetic with in-plane magnetization. They show clear in-plane fourfold magnetic anisotropy for all alloy concentrations and the relevant cubic anisotropy constant shows a strong composition and thickness dependence.

Epitaxially grown iron thin films (thickness: 8 A < d < 120 A) on Si(0 0 1) with body centred cubic structure have been structurally and magnetically studied at room temperature. All lilms are characterized by ferromagnetic properties as soon as the thickness reaches 4 ML. In-plane uniaxial and cubic magnetic anisotropy constants are measured on samples obtained by modifying the incidence angle of evaporating iron flux. The magnetization reversal mechanisms are analyzed by combining longitudinal magneto-optical Kerr effect of both parallel and transverse magnetization components. These mechanisms are strongly influenced by the nature of the magnetic anisotropies.

The magnetic properties of epitaxial iron films up to 80 monolayers (ML) thickness grown on Si(0 0 1) by using a template technique were investigated by means of superconducting quantum interference device and magneto-optic Kerr effect techniques. The thinnest films investigated (∼3 ML) exhibit a composition close to Fe3Si with a Curie temperature below room temperature (RT) and strong out-of-plane remanent magnetization that reflects the presence of a dominant second order surface anisotropy term. Thicker films (⩾4 ML) are ferromagnetic at RT with remanent magnetization in film-plane and a composition closer to pure Fe with typically 8–10% silicon content. When deposited at normal incidence such films show simple in-plane fourfold anisotropy without uniaxial contribution. The relevant fourth-order effective anisotropy constant K4eff was measured versus film thickness and found to change its sign near 18 ML. The origin of this remarkable behavior is investigated by means of a Neel model and mainly traced back to fourth-order surface anisotropy and magneto-elastic effects related to the large biaxial in-plane compressive strain up to 3.5% in the thinnest (⩽25 ML) films.

We demonstrate the possibility of growing good-quality epitaxial Fe films on a Si(001) substrate, opening up new prospects to prepare ferromagnetic superlattices on this substrate. A template technique prevents the formation of disordered interfacial iron silicides. Transmission electron microscopy reveals that the Fe layers are fairly uniform in thickness with abrupt interfaces and in majority epitaxial relationship Fe(001)[100]//Si(001)[100]. Both the diffraction data and the observation of Moire fringes indicate that the Fe lattice is almost relaxed towards its bulk bcc phase in thick layers [≥40 monolayers (ML)] but is still strained by the substrate in the thinnest films. Magneto-optical Kerr effect measurements show that the films evaporated at normal incidence with a thickness above 4 ML are ferromagnetic at room temperature and exhibit in-plane biaxial anisotropy.

Binary Fe(Si 1− x Fe x ) iron and ternary Fe 3− y Co y Si iron cobalt silicide thin films (thickness : 200 A) with local CsCl structure epitaxially grown at room temperature on Si(1 1 1) have been studied through X-ray magnetic circular dichroism (XMCD) and magneto-optic Kerr effect (MOKE) vector magnetometry. The binary Fe(Si 1− x Fe x ) films have ferromagnetic properties at room temperature in the range 0.09⩽ x 3− y Co y Si films are ferromagnetic as well in the whole range 0 y 3 Si) favored by the absence of orientation dependence of the fourth-order cubic term of the magnetocrystalline anisotropy energy in (1 1 1) crystallographic plane. The easy axis corresponds invariably to the direction normal to the incidence plane of the atomic flux during evaporation. The substitution of iron by silicon in Fe(Si 1− x Fe x ) films increases the coercive field but does not strongly affect the uniaxial anisotropy constant. In Fe 3− y Co y Si alloys, a similar trend is observed and the increase of coercive force may be related to defects generated by alloying. The change of the magnetic moments of Fe and Co versus y , as obtained by XMCD, can be understood in terms of simple models.

Iron silicide thin films (200 A Fe(Si 1− x Fe x ) with 0⩽ x ⩽1 and local cubic CsCl structure) have been grown by coevaporation at room temperature (RT) on Si(1 1 1). X-ray magnetic circular dichroism (XMCD) and magneto-optic Kerr effect (MOKE) measurements indicate that the films are ferromagnetic at RT for x ranging from 1 (pure Fe) to 0.15 (Fe 1.35 Si). The magnetization is parallel to the film surface, and the magnetic anisotropy is uniaxial, with the easy axis lying along a [1 0 1] Si crystallographic direction and the hard axis along a [1 2 1] Si direction of the substrate. MOKE measurements show that the magnitude of the saturation field increases with increasing Si concentration, while XMCD data indicate that the average local magnetic moment carried by the Fe atoms decreases with decreasing Fe concentration. Models which involve the diminution of the number of Fe nearest neighbors are proposed for the description of the behavior of the Fe moments.

We investigated the coupling of specific ferroelectric-superconducting composites with variable volume fraction, particularly because they have presented a superconducting transition at 85 K. The intra- and intergranular coupling of these composites has been considered from the resistivity and susceptibility measurements. Our results show that the transport properties of this kind of composite are governed by different mechanisms, depending on the volume fraction of the ferroelectric material, . Up to intragranular coupling exists between the YBCO superconducting grains, but when the electrical transport is greatly related to intergranular coupling. In this case, two distinct and superconducting phases are evidenced by the susceptibility measurements; they maintain the superconducting character of the composites. Moreover, at the superconducting percolation threshold, the electrical response exhibits some hysteresis giving evidence that internal polarization is important and can play a role in the composite properties.

We present experimental results obtained for R Ba 2 Cu 3 O 7 − x ( R = Y,Er) expitaxial thin films obtained through pulsed laser deposition (PLD) and grown on yttria stabilized zirconia (YSZ) and SrTiO 3 (STO) substrates. The films have been deposited by using low deposition rates ( f = 4 Hz) and with control of the film surface temperature rather than that of the sample holder leading to a high quality of the epitaxy.

High quality ErBa2Cu3O7−x thin films were grown by reactive laser deposition on yttria‐stabilized zirconia substrate. The structural and electrical properties of the samples were investigated by x‐ray double‐crystal diffractometry, texture analysis and reciprocal space mapping, and resistivity measurements, respectively. The best films were obtained by using high substrate temperature combined with a low fluence and low laser repetition rate. In these conditions the deposition rate results were very low, namely

Complex a.c. susceptibility measurements in a broad field range () have been made on Bi - Pb - Sr - Ca - Cu - O (Bi-2223 phase) bulk samples obtained by combined magnetic melt texturing and hot pressing. Highly anisotropic properties are observed. Improved intergranular coupling is obtained in the direction perpendicular to the applied stress and the magnetic field direction. An intragranular peak is also observed for the same direction. This is the first time that an intragranular loss peak has been clearly seen in a bismuth-based compound, which indicates that the intragranular contribution is strongly increased.

Low field a.c. susceptibilities of HgBa 2 Ca 2 Cu 3 O 8+δ (Hg-1223) and Bi 2 Sr 2 CaCu 2 O 8+δ (Bi-2212) have been studied. The loss peak of χ″, relevant to intergranular pinning, shifts to higher temperatures for increasing frequencies. The results can be fitted with an Arrhenius law, leading to activation energies E a ≈ 1eV, but the hopping frequencies 0 are not realistic. More realistic values can be obtained by introducing a Fulcher law or a power law which is also characteristic of strongly interacting systems.

The complex AC susceptibility of HgBa2Ca2Cu3O8+δ(Hg-1223) has been studied for DC magnetic fields 0 Oe≤HDC≤50 Oe and AC magnetic fields 0.1 Oe≤hAC≤70 Oe allowing the determination to be made of the irreversibility line both in the (HDC, T) plane and in the (hAC, T) plane. The critical dynamic field h∗c has furthermore been obtained in the low AC field limit. All these results are consistent with a strong increase of the intergranular pinning strength which is one order of magnitude higher than in similar as-sintered 123 compounds, suggesting possibilities for the critical currents.

Low AC field magnetic phase diagrams in the (hAC,T) plane have been deduced from AC susceptibility measurements for YBa2Cu3O7- delta sintered polycrystals, magnetically melt-textured polycrystals and single crystals. It is shown that dissipative regimes appear in all cases above a critical line located well below the irreversibility line, and the strongest shifts of the critical line against the irreversibility line are observed in magnetically melt-textured polycrystals. The relative positions of the irreversibility lines show that the increase of jc in magnetically melt-textured polycrystals is relevant to the creation of pinning sites with high activation energies.

Characterization of a superconducting transition is commonly achieved by a.c. susceptibility measurements. The technique involved is rather simple, but interpretation of experimental results in inhomogeneous compounds such as superconducting ceramics is difficult because of the great sensitivity to numerous experimental parameters which also govern sample fabrication techniques (geometry, stoichiometry and thermal treatment) and measuring conditions (frequency, magnitude and orientation of the a.c. and/or d.c. magnetic fields). We present an analysis of both the real part x′ and the imaginary part x″ of the complex susceptibility x = x′ + i x″ in the low field limit which allows an effective comparison between various superconducting ceramics. A review of experimental results includes comparison of flux pinning strength (given by the critical dynamic field h c ∗ ) and phase diagram in the ( h a.c. , T ) plane. The critical line obtained in such a way differs markedly from the so-called “irreversibility line”.

We discuss the problem of characterizing a superconducting transition and the question of comparing samples originating from different fabrication processes and/or obtained under various shapes or morphologies (bulk, wires, thin films, single crystals, …). We present two different methods for the analyses of the AC susceptibility (for both the real and the imaginary part) in the low field limit. Strength of flux pinning and intergrain/intragrain contributions are discussed. Both analyses are applied to different inhomogeneous superconductors like high-Tc compounds (YBCO, LCO, LSCO, LBCO, B(P)SCCO, NCCO), Chevrel phases, etc. The dynamic critical field given by such an analysis allows an estimation of the quality and/or homogeneity of the superconducting sample and is a measure of the first intergrain (or Josephson) critical field.

We discuss the problem of characterizing a superconducting transition and the question of comparing samples originating from different fabrication processes and/or obtained under various shapes or morphologies (bulk, wires, thin films, single crystals, …). We present different methods for the analysis of the very low field a.c. susceptibility (for both the real and the imaginary part). The dynamic critical field obtained from our analysis (which can be applied to different inhomogeneous superconductors like high T c compounds, Chevrel phases, etc.…) is a measure of the quality and/or homogeneity of the superconducting sample.

The controversial shapes of the transition in HTSC (e.g. width and ac field amplitude dependences) are resolved by introducing the dynamic critical field deduced from our susceptibility measurements. The dynamic critical field criterion (which is also a quality factor) is studied for various compounds (YBaCuO, BiSrCaCuO) and morphologies (bulk- and single crystals, thin films, wires) by studying the ac field dependences of both the real and imaginary parts of the initial susceptibility over nearly five orders of magnitude and down to very low ac fields (0.02 mOe h ac

A comparative study of the low field susceptibility of 123 high temperature superconducting compounds and Bi compounds is presented. Results are discussed using the dynamic critical field model of Mehdaoui et al. (1989,1990). The low critical dynamic fields and the corresponding low pinning energies obtained in the case of Bi compounds (when compared with 123 compounds) are consistent with other data about activation energy and explain the dependence of electrical resistivity upon measuring currents. The high temperature phase (Tc=110 K) also has much higher pinning than the low temperature phase (Tc=80 K) in the Bi compounds.

When discussing critical properties of inhomogeneous high temperature superconducting compounds it is preferable to compare experimental data collected from the greatest possible number of published results. However, such comparison is made difficult because of the wide variety of elaborate techniques, thermal treatments, characterization methods and sample morphologies involved in the experimental work reported in the literature. Here a phenomenological model, based on Clem's formulation and utilizing very low a.c. susceptibility measurements, is presented which demonstrates the existence of a critical field, h c ∗ , corresponding to the appearance of flux pinning. The analysis allows the classification of a large variety of high temperature superconductors including bulk samples, thin films and single crystals; the strength of the critical dynamic field (varying over three orders of magnitude: 50 mOe c ∗ Oe ) is a measure of the quality (and also homogeneity) of the sample. The analysis applies to YBaCuO compounds as well as to LaBaCuO and BiSrCaCuO compounds or Chevrel phases. The best quality appears to be for YBaCuO single crystals, while sintered BiSrCaCuO exhibits peculiar behaviour with very low h c ∗ or no h c ∗ at all.

Good quality body-centered cubic iron layers can be grown on Si(001) at room temperature using thin ${\mathrm{FeSi}}_{2}$ or ${\mathrm{CoSi}}_{2}$ silicide buffer layers. The in-plane and out-of-plane strains are measured by x-ray diffraction (XRD). Due to the difference in Fe and Si parameters of +5.6%, the thin Fe layers undergo a strong tetragonal distortion. For the samples deposited on ${\mathrm{FeSi}}_{2},$ the measured biaxial in-plane compressive strain ranges from values as large as -3.8% in the thinnest films (25 ML) to -1% in the thicker layers (g40 ML). In the samples deposited on ${\mathrm{CoSi}}_{2},$ a part of the iron layer clearly observable up to 40 ML, apparently grows in pseudomorphy with the silicon, whereas another dominant part above 15 ML partly relaxes and behaves as on ${\mathrm{FeSi}}_{2}$ templates but with systematically larger strains. The evolution of the in-plane cubic effective magnetic anisotropy constant versus Fe film thickness observed in previous work, can be explained by means of fourth-order (in spin) magnetoelastic coupling in the iron lattice with the strain components determined by XRD. Finally, the observed ratio between the perpendicular and in-plane strain components differs substantially from linear elasticity theory predictions and indicates the importance of anharmonic effects and/or defects in the description of the elastic properties of such films.

ac initial susceptibility of sintered, field textured, zone melted polycrystals and single crystals has been studied in the low field limit. Critical dynamic fields (h c ∗ ) and relative position of irreversibility line (I.L) and critical line (C.L) are consistent with the creation of strong pinning sites. High anisotropy is observed in the case of field textured samples.

The irreversibility line (I.L.) is often deduced from initial susceptibility measurements and taken at temperature TM corresponding to the maximum of the imaginary part χ″ of the susceptibility. It is expected that such a line plays a part analogous to that of the Tg (spin freezing temperature) in spin glasses, i.e. leads to a phase diagram in the H, T plane. But TM corresponds to the strongest dissipations and low field initial susceptibility measurements have shown that dissipations already occur well below the χ″ susceptibility maximum, and even in zero d.c. fields. We discuss an alternative way to define a critical line separating reversible and irreversible regimes; such a line is obtained (in a 3D extended phase diagram) by analyzing the χ′ real part of the initial susceptibility in the low a.c. field limit. It also represents the limit between dissipative and non dissipative regimes.

The authors present a detailed investigation of the AC field amplitude dependence of the initial complex susceptibility of YBaCuO compounds with various morphologies (bulk, thin film, single crystal) and BiSrCaCuO bulk compounds. They discuss the results together with published data in the critical dynamic field (hc*) model. hc* is a measure of the magnetic field above which vortices are unpinned giving rise to energy losses. The highest hc* are observed in YBaCuO single crystals. A comparison between YBaCuO and BiSrCaCuO polycrystals shows a better quality for the former. The magnetic transitions in YBaCuO compounds also show high sensitivity to grain size.

Texturing of high-temperature superconducting ceramics leads to an improved intergranular coupling. This is demonstrated on the basis of ac susceptibility measurements obtained when texturing Bi-2223 polycrystals through combined magnetic melt texturing and hot pressing (MMTHP) and Y123 bulk samples obtained through combined magnetic melt texturing and zone melting (MMTZM).

We discuss the magnetic properties of lead doped Bi-2223 bulk samples obtained through combined magnetic melt texturing and hot pressing (MMTHP). The ac complex susceptibility measurements are achieved over a broad ac field range (1 Oe{lt}h{sub ac}{lt}100 Oe) and show highly anisotropic properties. The intergranular coupling is improved in the direction perpendicular to the applied stress and magnetic field direction, and an intragranular loss peak is observed for the first time. A comparison is made with other bismuth-based compounds and it is shown that the MMTHP process shifts the ac irreversibility line (ac IL) toward higher fields. It is also shown that all the ac IL{close_quote}s for quasi 2D bismuth-based compounds show a nearly quadratic temperature dependence and deviate therefore strongly from the linear behavior observed in quasi 3D compounds and expected from a critical state model.{copyright} {ital 1997 Materials Research Society.}

We present experimental results obtained for high quality epitaxial thin films (film thicknesses around 5000 A; rocking curve FWHM down to 0.1°). These films are obtained by laser ablation of REBa 2 Cu 3 O 7−δ (RE = Y, Er) deposited on SrTio 3 and YSZ substrates. The superconducting properties have been studied by complex susceptibility in an extended AC field range ( h ac ≤ 300 Oe) and show sharp magnetic transition width and high critical currents (10 7 A cm −2 j c (77K) 8 A cm −2 ). The loss peak is only weakly depressed by an increasing AC field and the observed shifts are up to an order of magnitude lower than those observed for intragranular contributions in bulk samples. The agreement with the behaviour expected from a critical state model is also discussed.

Magnetically melt textured YBa 2 Cu 3 O 7−δ samples have been studied by AC initial susceptibility measurements in the low field limit. The critical dynamic fields h ∗ c and the relative position of the irreversibility line and of the critical line show that magnetic melt texturing leads to the creation of strong pinning sites. The anisotropy factor A is in agreement with the value obtained from magnetization under high DC fields. The A values are lower than in single cystals, but in agreement with the important orientation effects introduced by magnetic field texturing. These values also are typical of fabrication techniques involving a melting at some stage.

Characterizing a superconducting transition by initial susceptibility leads to highly variable results in inhomogeneous compounds and the shape of the transitions (both for χ′ and χ″) depends of numerous parameters such as: fabrication processes / thermal treatments, morphologies / shapes (bulk, wires, thin films, single crystals, powders), stoichiometry, coexistence of several phases, field orientation, etc... One can thus easily understand the difficulty encountered in comparing results obtained in different labs, using various experimental techniques applied on samples of different shapes!

We compare the irreversibility lines deduced from ac susceptibility measurements on Y-123, Bi- and Hg compounds obtained by various techniques (sintering, zone melting, magnetic field texturing). Field and frequency dependences are studied. Including results from the literature, our analysis indicate that fabrication methods containing a melting process favour the creation of pinning sites with high activation energies. Although weaker than in single crystals, an important anisotropy is induced by texturing processes.

Presents the results of an experimental study of electrodeposited amorphous Ni1-cPc alloys in the concentration range 0.5

We present the results of measurements of bulk magnetic and supreconducting properties in amorphous LaSmAu alloys obtained by liquid quenching. The magnetic data are compatible with a nearly trivalent state of Sm in the bulk. In contrast, the very strong depression of the superconducting transition in the dilute alloys suggests a Kondo or intermediate valence behaviour.

Experimental results are presented on the transport and magnetic properties of concentrated ion-chromium alloys Cr1-c in the composition range 16 at% 29 at%) and the antiferromagnetic (cFe

We have studied the AC initial complex susceptibility of sintered samples of high temperature superconducting YBaCuO compounds and the importance of using very low external magnetic AC fields (h AC h ∗ c which is much lower than the first critical (static) field H c1 . The characterization and the quality of the true transition (which is field independent) can only be obtained with measuring AC fields whose values are lower than the critical AC field. The shape of the magnetic transition is otherwise strongly affected by the amplitude of the AC field and makes difficult a comparison between samples of different origins, fabricated by different processes and characterized under different conditions.

The ac initial complex susceptibility of sintered samples of high temperature superconducting YBaCuO compounds is studied in detail. The importance of using very low external magnetic ac fields (hac < 10−3 Oe) is pointed out in order to prevent dynamical saturation (flux-pinning) when reaching the critical ac field h which is much lower than the first critical (static) field Hc1. The field, temperature, and frequency dependences of both real part (diamagnetic shielding) and imaginary part (power losses) are consistent with a rather large spread of critical temperatures over the volume: the highest (Tc = 90 K) at the surface and the lowest (50 < Tc < 80 K) in the inner part of the volume. It is also shown that this technique is a very useful tool for studying and/or controlling aging effects, water contamination, and thermal restoring treatments. Nous avons etudie en details la susceptibilite alternative en champs faibles de quelques composes frittes du type YBaCuO. Nous demontrons l'importance de l'emploi de champs magnetiques extremement faibles (hac < 10−3 Oe) afin d'eviter des phenomenes de saturation dynamique (ancrage des vortex) lors que l'on atteint le champ dynamique critique qui est nettement plus faible que le premier champ critique (statique) Hc1. L'evolution des parties reelle et imaginaire de la susceptibilite en fonction de la temperature, de la frequence et du champ magnetique sont en accord avec l'existence d'une distribution en volume des temperatures critiques: les temperatures les plus elevees (Tc = 90 K) correspondant a la surface et les temperatures les plus basses (50 < Tc < 80 K) correspondant a l'interieur du volume. La susceptibilite alternative en champs faibles apparait comme etant un outil extrěmement utile pour l'etude et/ou le controle des effets du vieillissement, de la contamination par la vapeur d'eau et des traitements thermiques.

Field, temperature and frequency dependences of the a.c. initial complex susceptibility of sintered samples of high-temperature superconducting YBaCuO compounds have been studied. We point out the importance of using very low external magnetic a.c. field (hac < 1 mOe) to prevent dynamic saturation (flux-pinning) on reaching the critical a.c. field hc∗, which is much lower than the first critical (static) field Hc1. Our results are also consistent with a rather large spread of critical temperatures through the volume: the highest (Tc = 90 K) is found at the surface and the lowest (50 K < Tc < 80 K) in the inner part of the volume. Aging effects and restoration by appropriate thermal treatment (15 days at 450 °C) are also controlled by studying the imaginary part of the susceptibility.

We present results on complex susceptibility measurements for the high temperature superconducting compound YBa 2 Cu 3 O x . It is found that the imaginary part of the susceptibility shows strong dependence both on frequency and amplitude of the external a.c. magnetic field, whereas the real part of the susceptibility shows weak dependence. These results are compared with the behaviour of other inhomogeneous type II superconducting systems. Meissner effects, power losses and current wave forms are consistent with the existence of weakly connected loops and/or flux pinning.

We compare our experimental results obtained for the complex susceptibility of YBaCuO compounds with other results available in the literature concerning YBaCuO as well as other high‐temperature superconducting oxides (LaBaCuO, BiSrCaCuO) or other inhomogeneous compounds like the Chevrel phase. We discuss a phenomenological model based on Clem’s formulation [Physica C 50, 153 (1988)]. We present a plot of all the experimental collected results, which allows a classification in terms of quality for a large variety of samples.

The authors present a systematic study of the magnetic transition from the paramagnetic to the ferromagnetic state in some nickel concentrated alloys NicT1-c (T=V, Cr, Mo, Ru, Cu). The magnetic measurements between 4K and 300K show that this transition occurs from the coupling between giant moments whose concentration increases when the nickel concentration increases up to the critical concentration ccr; their magnitude is the largest critical composition. A detailed study of NiV, NiMo and NiCu alloys shows that the magnetization results from giant moments whose magnitude increases when c to ccr and from nearly magnetic impurities in the vicinity of these moments. The existence of this nearly magnetic term is consistent with the temperature dependence of the resistivity in all the investigated alloys and with the magnetoresistance measurements in NiT alloys (T=V, Mo, Cu).

The a.c. initial susceptibility of bulk sintered samples of high temperature superconducting YBaCuO compounds has been studied in detail. By analyzing the field, temperature and frequency dependences of both real part (diamagnetic shielding) and imaginary part (power losses) we point out the compositional differences in oxygen content between the surface and the volume of a bulk sample. Our results are also consistent with a rather large spread of critical temperatures over the volume: the highest (Tc = 90K) at the surface and the lowest (50K < Tc < 80K) in the inner part of the volume. Results on aged and restored samples are also consistent with modifying of oxygen gradients.

Magnetization, NMR and coercive force measurements were performed on amorphous Ni1−cPc alloys for concentration ranging between 0.15 and 0.25. The experimental results show that the magnetism is not of the same nature below and above some critical concentration c0 which determines the concentration ranges: the first one (0.15 < c < 0.18) presents the characters of a weak homogeneous ferromagnetism, while inhomogeneities dominate the magnetic properties of the second one (0.18 < c < 0.25).

The Mossbauer spectroscopic study on some concentrated iron-chromium alloys FexCr1-x (with 0.2 < x < 0.3) gives evidence for the occurrence of a superparamagnetic state, which accounts for the typical transport and magnetic properties observed in these alloys.

Electrical resistivity measurements on diluted copper based alloys (at T=70K) show different behaviour with nearly magnetic d impurities (Ni, Co), nonmagnetic d impurities (Rh) and s-p impurities (Zn, Ga, Ge). Only for the first kind a well defined temperature law is obtained on the breakdown of Matthiessen's rule. For the other kinds, the absence of any well defined Tn law is attributed to simultaneous scattering by at least two processes.

Low temperature transport properties of concentrated Ni-Fe alloys are studied and analysed in the two band conduction model. The obtained values are compatible with the occurrence at the Fermi level of a high density of states for the majority spin band.

We study the electrical resistivity of concentrated nickel alloys (NiV, NiCr, NiFe, NiCo, NiMo, NiRu, NiIr) between 4 and 300°K; we relate these experimental data to the electronic structure of these alloys with special attention concerning the critical concentrations for magnetic transitions.

Bulk magnetization measurements on binary and ternary cobalt-based alloys with transitional elements (Cr, Mn, Zr, Nb, Mo, Ru, Hf, Ta, W, Re, Os, Ir) confirm the existence of a periodic effect; the number of d electrons going from the spin-up band to the spin-down band depends on the series from which the transitional element is taken. The results are analyzed in terms of virtual bound states, experimental data giving the bound state position, obtained by dissolving a transitional impurity in a cobalt matrix, in relation to the Fermi level. Furthermore, there are no interactions between transitional impurities dissolved in cobalt at sufficiently small concentrations (c < 5%)