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We report evidence that ephaptic interactions may occur between intact mammalian myelinated nerve fibres and not only between demyelinated or damaged mammalian nerve fibres or nerve cells as analysed in previous studies. The ephaptic interactions were investigated between nerve fibres traversing the lumbar dorsal roots and between bundles of fibres in the sciatic nerve in anaesthetized rats in vivo. The interactions were estimated by comparing the excitability of nerve fibres originating from one of the hindlimb nerves (peroneal or sural) under control conditions and when the stimulation of these fibres was combined with stimulation of another nerve (tibial). An increase in nerve volleys recorded from group I muscle afferents in the peroneal nerve and of the fastest skin afferents in the sural nerve was used as a measure of the increase in the excitability. The excitability of these fibres was increased during a fraction of a millisecond, coinciding with the period of passage of nerve impulses evoked by the conditioning stimulation of the tibial nerve. The degree of the increase was comparable to the increases in the excitability evoked by 1-2 min lasting fibre polarization. Ephaptic interactions were found to be more potent and with longer lasting after-effects within the dorsal roots than within the sciatic nerve. We postulate that ephaptic interactions may result in the synchronization of information forwarded via neighbouring afferent nerve fibres prior to their entry into the spinal cord and thereby securing the propagation of nerve impulses across branching points within the spinal grey matter.

Cobalt ferrite nanopowders were successfully synthesized by the coprecipitation method and subsequent calcinations at 873 and 1073 K. The effects of the thermal treatments on the crystal structure, particle size and magnetic properties of the nanocompounds were investigated. The particle sizes were determined from transmission electron microscopy and an increase in sizes with the increment in calcination temperature was observed. The mean particle sizes were 29 and 42 nm, for samples calcined at 873 and 1073 K, respectively. By X-ray diffraction it was determined that the nanoparticles crystallized in the cubic spinel structure. Additionally, Fourier transform infrared spectroscopy studies confirms the presence of spinel metal oxide. The magnetization measurements as a function of the temperature and the applied magnetic field suggested that a large part of the nanoparticles calcined at 873 K present a superparamagnetic behavior at room temperature, while those calcined at 1073 K are mainly in the blocked regime at temperatures below 320 K. In addition, remarkably high coercivities of approximately 10.7 and 12.4 kOe were observed at low temperatures, for the nanopowders calcined at 873 and 1073 K, respectively.

In this study we have determined for first time the magnetic anisotropy field (HA) of Strontium Ferrite (SFO, SrFe12O19) nanoparticles of different morphologies using the Singular Point Detection (SPD) technique.

The chemical and physical properties of the double perovskite Pb2FeMoO6 are systematically studied by means of structural and magnetic characterization. The compound crystallizes in the cubic Fm3¯m space group, with partial cation order involving iron and molybdenum at the perovskite B site. Structural and Mössbauer characterization points to the presence of nanometer-sized antiphase domains within the ordered matrix giving rise to two iron populations, characterized by different chemical environments, with the same weight but different valence (0.3 electrons) and inequivalent magnetic anisotropy. This structural feature deeply affects the properties of the compound: Mössbauer and EPR measurements show a high-temperature superparamagnetic-like behavior ascribed to weak magnetic interactions occurring between the antiphase domains and the rest of the sample. However, below 270 K ferrimagnetic ordering of the atomic moments is observed by neutron diffraction and SQUID magnetometry, with the onset of blocked long range magnetic interactions on the Mössbauer timescale involving both the antiphase domains and the ordered matrix below 230 K. The superparamagnetic-like behavior is ascribed to the presence of low anisotropy barriers, giving rise to an extremely thin hysteresis loop at 5 K, with a very small coercive field and remnant magnetization. The observed saturation magnetization of 1.75 µB per f.u. is in agreement with the magnetic structure determined by neutron diffraction, with the two symmetry independent sites producing a ferrimagnetic resultant µS = 1.59 µB.

This review aims to highlight the important contribution of the cerebellum in the Anticipatory Postural Adjustments (APAs). These are unconscious muscular activities, accompanying every voluntary movement, which are crucial for optimizing motor performance by contrasting any destabilization of the whole body and of each single segment. Moreover, APAs are deeply involved in initiating the displacement of the center of mass in whole-body reaching movements or when starting gait. Here we present literature that illustrates how the peculiar abilities of the cerebellum i) to predict, and contrast in advance, the upcoming mechanical events; ii) to adapt motor outputs to the mechanical context, and iii) to control the temporal relationship between task-relevant events, are all exploited in the APA control. Moreover, recent papers are discussed which underline the key role of cerebellum ontogenesis in the correct maturation of APAs. Finally, on the basis of a survey of animal and human studies about cortical and subcortical compensatory processes that follow brain lesions, we propose a candidate neural network that could compensate for cerebellar deficits and suggest how to verify such a hypothesis.

It has been observed that, after 2 hours of aerobic exercise, plasma interleukin-6 (IL-6) increases whereas nuclear concentrations of enzyme DNA methyltransferase (DNMT) 3B significantly decreased in peripheral blood mononuclear cells (PBMCs), with no change observed in DNMT3A. The aim of the present study was to detect differences in these changes induced by exercise in plasma IL-6 levels as well as in PBMC nuclear concentrations of DNMT3A and DNMT3B, in relation to age and sex. Four groups were studied: 12 young men (24.8 ± 1.77 years old), 12 young women (23.8 ± 1.81 years old), 12 adult men (45.8 ± 1.82 years old), 12 adult women (mean 44.5 ± 2.07 years old). Participants had to run at 60% of maximal oxygen consumption (VO2max) for 120 minutes, interspersed with sprints at 90% of VO2max for the last 30 seconds of every 10 minutes. About 250 μL of PBMCs (1 × 10 cells) were treated with 100 μL of either pre-exercise plasma or post-exercise plasma and nuclear DNMT3A and DNMT3B concentrations were quantified. No change in nuclear concentration of DNMT3A following the exercise was observed. Conversely, nuclear concentrations of DNMT3B significantly decreased, with a reduction of about 78% in young men, 72% in young women, 61% in adult men, and 53% in adult women. Moreover, a strong positive correlation between the nuclear concentration of DNMT3B in PBMC following stimulation with post-exercise plasma and post-exercise plasma concentrations of IL-6 was observed in all the 4 studied groups. This study confirms that a single bout of endurance exercise is sufficient to decrease nuclear concentrations of DNMT3B and thus protein upregulation. Moreover, the epigenetic mechanisms induced by exercise apparently cause more intense changes in men than in women and that, in both of them, this effect seems to decrease with age.

The study of singularities in the magnetization curve of magnetic materials is since a long time a well known tool to gain insight into the material properties. Such singularities are usually due to discontinuous magnetization processes related to magnetic anisotropy, therefore an ideal investigation scheme would comprise magnetization measurements along the symmetry axis of a single crystal. As a matter of fact, one has to often deal with polycrystalline samples: in that case, however, the singularities can still be detected at the same positions as for the single crystal case. In this paper we focus on ferrimagnetic materials with uniaxial magnetic anisotropy. After recalling how theory allows us to calculate the critical fields at which singularities occur when the magnetic field is applied along a symmetry direction, we show that a new type of singular point not yet reported in the literature can exist. Such new singularity appears only in polycrystalline samples. We derive its analytical expression and we also show that, in spite of the need to overcome the exchange interaction, combinations of the material parameters can occur for which it falls inside experimentally accessible region. (C) 2015 Elsevier B.V. All rights reserved

The magnetocrystalline anisotropy (MAE) of ${\mathrm{Ni}}_{2\ensuremath{-}x}{\mathrm{Pt}}_{x}\mathrm{MnGa}(0\ensuremath{\le}x\ensuremath{\le}0.25)$ alloys are investigated using the singular point detection technique and density functional theory. A slight reduction in MAE as compared to that of ${\mathrm{Ni}}_{2}\mathrm{MnGa}$ is observed due to Pt substitution. The calculated MAE varies almost linearly with the orbital moment anisotropy. A competition between the elastic and the chemical contributions explains the observed trend of the MAE with increasing Pt content. The large MAE in combination with the previously reported increase of the martensitic transition temperature makes these alloys promising candidates for ferromagnetic shape memory applications near room temperature.

Effects of direct current (DC) on nerve fibers have primarily been investigated during or just after DC application. However, locally applied cathodal DC was recently demonstrated to increase the excitability of intraspinal preterminal axonal branches for1 h. The aim of this study was therefore to investigate whether DC evokes a similarly long-lasting increase in the excitability of myelinated axons within the dorsal columns. The excitability of dorsal column fibers stimulated epidurally was monitored by recording compound action potentials in peripheral nerves in acute experiments in deeply anesthetized rats. The results show that

Key points Trans-spinal DC stimulation affects both postsynaptic neurons and the presynaptic axons providing input to these neurons. In the present study, we show that intraspinally applied cathodal current replicates the effects of trans-spinal direct current stimulation in deeply anaesthetized animals and affects spinal neurons both during the actual current application and during a post-polarization period. Presynaptic effects of local cathodal polarization were expressed in an increase in the excitability of skin afferents (in the dorsal horn) and group Ia afferents (in motor nuclei), both during and at least 30 min after DC application. However, although the postsynaptic facilitation (i.e. more effective) activation of motoneurons by stimuli applied in a motor nucleus was very potent during local DC application, it was only negligible once DC was discontinued. The results suggest that the prolonged effects of cathodal polarization are primarily associated with changes in synaptic transmission. Abstract The present study aimed to compare presynaptic and postsynaptic actions of direct current polarization in the spinal cord, focusing on DC effects on primary afferents and motoneurons. To reduce the directly affected spinal cord region, a weak polarizing direct current (0.1–0.3 μA) was applied locally in deeply anaesthetized cats and rats; within the hindlimb motor nuclei in the caudal lumbar segments, or in the dorsal horn within the terminal projection area of low threshold skin afferents. Changes in the excitability of primary afferents activated by intraspinal stimuli (20–50 μA) were estimated using increases or decreases in compound action potentials recorded from the dorsal roots or peripheral nerves as their measure. Changes in the postsynaptic actions of the afferents were assessed from intracellularly recorded monosynaptic EPSPs in hindlimb motoneurons and monosynaptic extracellular field potentials (evoked by group Ia afferents in motor nuclei, or by low threshold cutaneous afferents in the dorsal horn). The excitability of motoneurons activated by intraspinal stimuli was assessed using intracellular records or motoneuronal discharges recorded from a ventral root or a muscle nerve. Cathodal polarization was found to affect motoneurons and afferents providing input to them to a different extent. The excitability of both was markedly increased during DC application, although post-polarization facilitation was found to involve presynaptic afferents and some of their postsynaptic actions, but only negligibly motoneurons themselves. Taken together, these results indicate that long-lasting post-polarization facilitation of spinal activity induced by locally applied cathodal current primarily reflects the facilitation of synaptic transmission.

Transcranial direct current stimulation (tDCS) affects neurons at both cortical and subcortical levels. The subcortical effects involve several descending motor systems but appeared toberelativelyweak,asonlysmallincreasesintheamplitudeofsubcorticallyinitiateddescending volleys and a minute shortening of latencies of these volleys were found. The aim of the present study was therefore to evaluate the consequences of facilitation of these volleys on the ensuing muscle activation. The experiments were carried out on deeply anaesthetized rats without neuro- muscular blockade. Effects of tDCS were tested on EMG potentials recorded from neck muscles evoked by weak (20-60 μA) single, double or triple stimuli applied in the medial longitudinal fascicle (MLF) or in the red nucleus (RN). Short latencies of these potentials were compatible with monosynaptic or disynaptic actions of reticulospinal and disynaptic or trisynaptic actions of rubrospinal neurons on neck motoneurons. Despite only weak effects on indirect descending volleys, the EMG responses from both the MLF and the RN were potently facilitated by cathodal tDCSanddepressedbyanodaltDCS.Boththefacilitationandthedepressiondevelopedrelatively rapidly (within the first minute) but both outlasted tDCS and were present for up to 1 h after tDCS.Thestudythusdemonstrateslong-lastingeffectsoftDCSonsubcorticalneuronsintherat, albeit evoked by an opposite polarity of tDCS to that found to be effective on subcortical neurons in the cat investigated in the preceding study, or for cortical neurons in the humans.

This work aims at understanding the large reduction of superconducting critical temperature Tc observed in YSr 2 Cu 3 0 6+x as compared to its YBa 2 Cu 3 O 6+x counterpart (ΔTc = -30 K ). We report on a combined study of structural and electronic properties of RESr 2 Cu 3 O 6+x(RE = Y, Yb) polycrystalline samples. Neutron diffraction data and Cu NQR spectra show that, contrary to REBa 2 Cu 3 O 6+x RESr 2 Cu 3 O 6+x is locally tetragonal and no CuO chains are formed. This arises from the random occupancy of oxygen along the a- or b- direction in the basal planes. Ab-initio calculations of the electronic structure using the full-potential linearized-augmented-plane-wave method (FLAPW) in the local density approximation (LDA) suggest that the CuO chains are not formed because of the large elastic strain associated with the orthorhombic distortion produced by the chain formation. In addition, by using a [Formula: see text] supercell simulating the absence of chains, we find that oxygen disorder greatly alters the band structure near the Fermi level. Our analysis indicates that this alteration leads to a reduction of hole transfer from the CuO chains to the CuO 2 planes, which accounts for the reduction of Tc experimentally observed.

The role of interface morphology in the magnetic behavior of FePt/Fe exchange-coupled systems has been considered. Hard/soft bilayers with different interface morphologies were obtained by depositing Fe thin layers on FePt epitaxial layers with different morphologies, but all with a high degree of L10 ordering and high coercivity. It was found that the hard/soft coupling can be tuned by changing the FePt morphology, allowing tailoring of the hysteresis loops and modification of the magnetic regime at a fixed Fe thickness (from Rigid Magnet to Exchange-Spring magnet). Remarkably, all bilayer series showed a drastic reduction in coercivity with increasing Fe thickness to 3.5 nm (μ0HC ⩽ 1.1 T).

Single crystals of the magnetic semiconductor CoIn0.5Cr1.5S4, belong to the system CoIn(2-2X)Cr(2X)S4 with x = 0.75, was grown by the chemical transport method. X-ray powder diffraction characterization by the Rietveld method indicated that CoIn0.5Cr1.5S4 crystallizes in the space group Fd-3m, Z = 8, with a = 10.0700(6) A and V = 1021.2(1) A3, in a normal spinel structure. The temperature dependence of the DC magnetization suggests that the studied compound presents a ferromagnetic behavior with a Curie temperature Tc = 220 K. Sharp spin-glass like behavior was found also. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effects of trans-spinal direct current (DC) stimulation (tsDCS) on specific neuronal populations are difficult to elucidate, as it affects a variety of neuronal networks. However, facilitatory and depressive effects on neurons processing information from the skin and from muscles can be evaluated separately when weak (0.2-0.3 μA) DC is applied within restricted areas of the rat spinal cord. The effects of such local DC application were recently demonstrated to persist for at least 1 h, and to include changes in the excitability of afferent fibres and their synaptic actions. However, whether these effects require activation of afferent fibres in spinal neuronal pathways during DC application, i.e. whether they are activity-dependent or activity-independent, remained an open question. The aim of the present study was to address this question by analysing the effects of local DC application on monosynaptic actions of muscle and skin afferents (extracellular field potentials) and afferent fibre excitability. The results revealed that long-lasting post-polarization changes evoked without concomitant activation of afferent fibres replicate changes evoked by stimuli applied during, before and after polarization. The study leads to the conclusion that the reported effects are activity-independent. As this conclusion applies to the local effects of DC application in at least two spinal pathways and to the effects of both cathodal and anodal polarization, it indicates that some of the more widespread effects of trans-spinal and trans-cranial stimulation (both tsDCS and transcranial DC stimulation) may be activity-independent. The results may therefore contribute to the design of more specific DC applications in clinical practice.

We have exploited the pseudomorphic growth of the magnetically soft Fe3Pt phase on top of L10- FePt to obtain fully epitaxial soft/hard nanocomposites on both MgO(100) and SrTiO3(100). The magnetic properties of this new nanocomposite system, driven by the soft/hard exchange- coupling, can be tailored by varying soft phase thickness, soft phase magnetic anisotropy and substrate. Coercivity is strongly reduced by the addition of the soft phase, a reduction which is definitely affected by the nominal composition of the soft phase and by the substrate choice; similarly is the magnetic phase diagram of the composite system. Coercive field decreases down to 21% of the hard layer value for Fe3Pt(5 nm)/FePt(3.55 nm) nanocomposites on SrTiO3; this maxi- mum coercivity reduction was obtained with a nominal atomic content of Fe in the soft phase of 80%.

Zero-field μ SR experiments were performed on a series of polycrystalline samples of AA 3 ′ Mn 4 O 12 double perovskites ( A = Na + , Ca 2 + , La 3 + ; A ′ = Cu 2 + , Mn 3 + ) synthesized under high pressure. Spontaneous precession frequencies, of comparable magnitude to those previously reported in LaMnO 3 , were observed in all the family members except CaMn 7 O 12 . For all the samples, μ SR yielded determinations of the magnetic transition temperatures and of the order parameter in agreement with other techniques, but also revealed a peculiar phase separation in CaMn 7 O 12 , absent in the other compounds.

The BiMnO3 perovskite is a very interesting multiferroic material that, once synthesized at high pressure and high temperature, survives as a metastable phase at ambient conditions. We investigated ceramic samples prepared in different conditions (temperature, pressure, and composition), and the existence of polymorphism at room temperature was clearly evidenced by electron diffraction and high-resolution electron microscopy in all the samples. A new polymorph, characterized by a different distortion of the perovskite basic cell, was found to coexist as a minor phase with the well-known C2 monoclinic form. The new polymorph, which can be described by a triclinic (pseudorhombohedral) superstructure with a = 13.62 angstrom, b = 13.66 angstrom, c = 13.66 angstrom, alpha = 110.0 degrees, beta = 108.8 degrees, and gamma = 108.8 degrees, is mostly segregated at the grain surface. Magnetic characterizations revealed for this second form a critical temperature of 107 K, a few degrees above the ferromagnetic transition of the monoclinic C2 form measured at 99 K. The new phase disappears by reheating the samples at ambient pressure, suggesting the idea of a higher energy polymorph, which kinetically converts in the usual phase once a sufficient temperature has been achieved.

Vn-xTixO2n-1 Magneli phases have been synthesized under vacuum in powder form (n = 4, 0 ≤ x ≤ 0.4) and crystals (n = 4 and 5, x = 0.5 and 1.4, respectively), grown by chemical vapour transport in closed ampoules. TeCl4 and NH4Cl were used as transporting agents. Needle-shaped crystals as long as 200-300 micrometers or 2-3 mm were obtained when in presence of NH4Cl or TeCl4, respectively. The powder and crystal structures were examined by X-ray diffraction and the transport and magnetic characteristics were measured.. The powders resulted to be single-phase and the relevant composition was assumed to be equal to the nominal one. The overall stoichiometry of compounds, n, was determined from single crystal X-ray diffraction data. The Ti content, x, was deduced from the elementary cell volume, by applying the Vegard law. Crystals were mainly untwinned and of good quality. The elementary cell of both, powders and crystals, was triclinic (P-1) and did not change with doping. DC electrical resistivity of the crystals was measured in a four-points (van der Pauw) configuration. DC magnetic susceptibility of the powders was measured in a SQUID magnetometer. The Ti doping was found to progressively smooth and finally to suppress the magnetic transitions occurring in the V4O7. The metal-insulator transitions observed in V4O7 and V5O9, at around 235 and 125 K respectively, were not observed in the doped crystals, thus indicating some significant change of the electronic structure of the V oxides. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This study examines the effect of ultrasonically nebulized distilled water inhalation on the systemic histamine hyperreactivity of Toxocara canis-infected mice.Uninfected and T. canis-infected mice received an intravenous sublethal dose of histamine and lethality rates were documented. At 24 days post infection, infected mice received ultrasonically nebulized distilled water inhalation for 1 h. Twenty-four hours later histamine levels were determined in bronchoalveolar lavage fluid as well as histamine lethality and toluidine blue-stained mast cell number in the lung.T. canis-infected mice showed increased lethality after exposure to histamine in comparison to uninfected mice. Ultrasonically nebulized distilled water inhalation prevented histamine-induced lethality and reduced toluidine blue-stained mast cell numbers in the lung.The correlation between decreases in stained mast cells in the lung after ultrasonically nebulized distilled water inhalation and inhibition of histamine-induced lethality in these animals suggests participation of mast cells in the phenomenon and could be helpful in understanding the mechanisms of hyperreactivity during helminth parasite infections.

By using a simple single-pass reel-to-reel system, we demonstrate a simple and robust in-situ route for the continuous deposition of 1-2 m long Coated Conductors (CC) consisting of 1 /spl mu/m thick superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) films deposited by thermal co-evaporation onto 100 nm thick CeO/sub 2/ buffered cube textured Ni tapes. The buffer layer was deposited by either e-beam or thermal evaporation using respectively ceria or metallic cerium. The structural and morphological properties of the samples were investigated by X-ray /spl thetav/-2/spl thetav/ Bragg-Brentano, and pole figure diffraction, Nomarsky optical microscopy and Scanning Electron Microscopy (SEM) analysis. The 123 composition was controlled during deposition by means of an atomic absorption system. The optimized buffer layer and YBCO layer are grown at 690/spl deg/C in respectively forming gas and oxygen partial pressures of 5/spl times/10/sup -5/ mbar. These conditions ensure the growth of dense and crack-free layers with good biaxial texture, as indicated by FWHM's values in the 5-7/spl deg/ range for both in- and out-of-plane orientations. Zero-resistance critical temperatures T/sub c/=86-87 K with transition widths /spl Delta/T/sub c/

In the present work we report on the anisotropy properties of Sr1–xLaxFe12–xCoxO19 up to x=0.4. The study has been carried out on oriented polycrystalline samples by means of the Singular Point Detection techniques, the initial susceptibility, the magnetization curves and the differential susceptibility in the temperature range from 4.2 up to 300 K. The analysis of the results takes advantage of computer simulations based on an extended Stoner-Wohlfarth model and leads to the accurate determination of anisotropy constants K1, K2, K3 and coefficients χ2,0, χ4,0, χ6,0, as functions of x and temperature. The results emphasise the strong effect of Co-ions on the high order anisotropy terms and are discussed in terms of the Slonczewski one-ion model. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Measurements of magnetization and of resistivity under pressure on Ba 1-x Sr x VS 3 single crystals show that Sr-induced chemical pressure progressively weakens the antiferromagnetic correlations responsible for the metal-insulator transition. The antiferromagnetic ordering temperature, TX = 30 K at x = 0, vanishes at x = 0.08. At larger x, a ferromagnetic order appears with TC = 21.5 K at x = 0.18. The key-parameter favoring the metallic state is found to be the compression of the VS 6 octahedra and we predict a metallic state at 0 K for a V–S distance of 2.33 Å. The stabilization effect of the metallic state provided by the chemical pressure is supported by first principles band structure calculations performed by using the Vienna ab initio simulation package (VASP) within the projector augmented–wave (PAW) method in the local density approximation (LDA) + U scheme.

We have monitored the evolution of the structure of multilayered-granular films deposited by alternately growing thin cobalt layers and thicker copper layers by RF-sputtering. In particular, we have observed how the reduction of the Co layer thickness affects the overall structure of the samples and the morphology of the magnetic particles. Synchrotron radiation has been used to do diffraction, reflectivity and small angle scattering measurements, performed in anomalous configuration, in order to increase the low Co–Cu electron density contrast. We find that the samples are made of large columnar grains whose size depends on Co nominal thickness. A good agreement between the results of the X-ray analysis and the magnetic properties of the samples has been found.

The compounds Pr2(CoxFe1−x)17 with x=0, 0.1, 0.2 exhibit a complex behaviour of the magnetic anisotropy: the occurrence of a normal approach to saturation, a type 1 FOMP, a double transition and a type 2 FOMP, are found in different temperature intervals. This phenomenology can be explained if a two sublattice system having competing anisotropies and the occurrence of canting angles between magnetic sublattices, during the magnetisation process, are considered.

By means of synchrotron x-ray and electron diffraction, we studied the structural changes at the charge order transition ${T}_{\text{CO}}=176$ K in the mixed-valence quadruple perovskite $({\mathrm{NaMn}}_{3}){\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$. Below ${T}_{\text{CO}}$ we find satellite peaks indicating a commensurate structural modulation with the same propagation vector $\mathbf{q}=(1/2,0,\phantom{\rule{0.16em}{0ex}}\ensuremath{-}1/2)$ of the CE magnetic structure that orders at low temperatures, similarly to the case of simple perovskites such as ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3}$. In the present case, the modulated structure, together with the observation of a large entropy change at ${T}_{\text{CO}}$, gives evidence of a rare case of full ${\mathrm{Mn}}^{3+}/{\mathrm{Mn}}^{4+}$ charge and orbital order, consistent with the Goodenough-Kanamori model.

We report on a systematic study of the structural, magnetic, and transport properties of high-purity 1T-VS2 powder samples prepared under high pressure. The results differ notably from those previously obtained by deintercalating Li from LiVS2. First, no charge-density wave (CDW) is found by transmission electron microscopy down to 94 K, though ab initio phonon calculations unveil a latent CDW instability driven by an acoustic phonon softening at the wave vector qCDW≈(0.21,0.21,0) previously reported in deintercalated samples. A further indication of latent lattice instability is given by an anomalous expansion of the V-S bond distance at low temperature. Second, infrared optical absorption and electrical resistivity measurements give evidence of nonmetallic properties, consistent with the observation of no CDW phase. On the other hand, magnetic susceptibility and NMR data suggest the coexistence of localized moments with metallic carriers, in agreement with ab initio band structure calculations. This discrepancy is reconciled by a picture of electron localization induced by disorder or electronic correlations leading to a phase separation of metallic and nonmetallic domains in the nm scale. We conclude that 1T-VS2 is at the verge of a CDW transition and suggest that residual electronic doping in Li deintercalated samples stabilizes a uniform CDW phase with metallic properties.

The superconducting fulleride (NH3) x NaK2C60 has a cubic structure with lattice parameter (a) and transition temperature (Tc) depending on x. The relation between these two parameters was found, however, to be opposite to what is expected from the BCS theory (and observed in the other fullerides). To better understand the origin of this anomaly we have measured the electronic spin susceptibility with SQUID magnetometry and NMR in two differently doped samples. The relation between Tc and the density of states at the Fermi energy is found to be opposite to the Migdal-Eliashberg prediction. The 13C-MAS measurement of the isotropic part of the 13C Knight shift qualitatively confirms this result. 13C NMR relaxation measurements validate the interpretation of the spin susceptibility in terms of density of states and rule out the presence of strong antiferromagnetic correlations in the Fermi liquid.

The singular point detection (SPD) technique has been used to measure in a pulsed-field apparatus ( H max =300 kOe) the temperature dependence of the anisotropy and the critical field of different first-order transitions (FOMP), which are induced by the applied magnetic field in the intermetallic compound Pr 2 Fe 17 . This compound exhibits complex behaviour of the magnetic anisotropy: with decreasing temperature, subsequently, a normal approach to saturation, a type-I FOMP and a double transition are found in different temperature intervals. By performing computer simulations of the magnetisation processes, it has been found that the observed complex phenomenology in Pr 2 Fe 17 can be explained if the occurrence of canting angles between magnetic sublattices having competing anisotropies is taken into account.

The high-field installation at the MASPEC Institute is described. The increase of energy up to 1 MJ has recently been implemented, thus permitting the generation of fields up to 60 T with a pulse duration of 40 ms. The planned experiments are magnetocrystalline anisotropy studies of single crystals using magnetization curves, while polycrystalline samples are studied with the singular point detection technique (SPD). The two methods can be used to study critical field and critical magnetization in first-order magnetization processes (FOMP) that are field-induced magnetic transitions. Transport measurements both in semiconductors and superconductors are planned.

The paper deals with the application of cathodic protection of steel in atmospherically exposed reinforced concrete. The use of this technique to control corrosion rate in chloride contaminated constructions and to improve the corrosion resistance of reinforcement in new structures expected to become contaminated is discussed. The more recent applications of cathodic protection on carbonated concrete are also considered. For each type of application, principles and operating conditions (potential and current applied, throwing power, risk of hydrogen embrittlement in the case of prestressed structures) are discussed. Examples of cathodic protection and prevention in bridges, and buildings are reported.

The overdoped regime in Y 1-x Ca x Ba 2 Cu 3 O 7, for x=0.05 and x=0.10 (Tc(0)=82 K and Tc(0) = 73.8 K respectively) is studied by means of 89 Y NMR relaxation and SQUID magnetization measurements. It is shown that for hole concentration close to 0.19, where a critical point is suspected and where the antiferromagnetic correlations should disappear, 1/(T1T) is strictly constant from room temperature down to Tc. This behavior is also observed in the sample at Ca-content 0.10, where the hole concentration is 0.203. The magnetization as a function of temperature and the isothermal magnetization curves, reveal the occurrence of a marked enhancement of the fluctuating diamagnetism in the overdoped regime, with respect to optimally doped YBCO. The magnetization data cannot be justified by anisotropic Ginzburg-Landau functional for the free energy or by scaling arguments. These findings are tentatively related to superconducting "drops" created above Tc or to phase fluctuations in restricted dimensionality.

We prepared polycrystalline samples of YBa 2 Cu 2( Cu 1-x M x) O 6+w, where M (=Sc, Cr, V, Fe, Al and Au) substitutes copper in the chain site, and measured their transport and magnetic properties. The substitution level x was 0.05 and 0.10 for each substituent. We determined the solubility of the different metals and the dependence of Tc, irreversibility lines and critical current density jc on M and x. An improvement of jc by a factor larger than 2 was obtained in the Fe-, Al-, Cr- and V- substituted materials. No improvement of the irreversibility line was obtained for any substituent.

The intermetallic compound CeCo3 has been irradiated at GANIL by 1 GeV Pb-208 ion beams. The irradiated samples are found to be strongly amorphised. A track diameter of 8 nm is found. The magnetic properties of the irradiation induced CeCo3 amorphous phase have been studied in detail and found substantially different with respect to those of amorphous CeCo3 obtained by conventional methods. In particular, an increase of about 200 K in the Curie temperature is observed, suggesting that a different type of chemical short range order might have been stabilized by irradiation. (C) 1998 Elsevier Science B.V. All rights reserved.

The compound (NH3)xNaRb2C60 has been studied by SQUID magnetometry, 23 Na and 1 H NMR. A 23 Na / 1 H double irradiation NMR experiment evidences a close distance between Na ions and ammonia, confirming the octahedral occupancy of this cluster which is usually observed in the ammonia intercalated fullerides. The Knight shift interaction of the ammonia protons with the conduction electrons is of pure anisotropic nature and is detected as a field dependent broadening of the 1 H NMR lines at low temperature. The recovery of the proton magnetisation follows a single exponential at all the investigated temperatures and fields. A Korringa behaviour is observed below 65 K and a clear Hebel–Slichter coherence peak is detected just below Tc. The Korringa relation does not hold and the Knight shift enhancement suggests the presence of a Coulomb repulsion.

Plate-like single crystals of magnetic semiconductor FeIn 2 Se 4 were grown with a chemical vapour transport technique. The X-ray powder diffraction analyses suggest that the compound crystallize in the hexagonal structure with space group P3m1. We have performed dc magnetization measurements at different magnetic fields on the diluted magnetic semiconductor FeIn 2 Se 4 . Low field magnetizations measurements shows irreversibility in the DC magnetization, as evidenced by field cooled and zero field cooled measurements below 17 K, suggesting a spin-glass like behaviour. The high-temperature susceptibility data follow a typical Curie–Weiss law with θ =−183±2 K which suggest the presence of predominant antiferromagnetic interactions with high degree of frustration. The randomness and frustration necessary for spin-glass behaviour are explained in a manner compatible with the cation and charge ordering present in the material.

We report zero-field μ SR experiments on two Ba 1 - x La x VS 3 samples ( x = 0 and 0.1 ). Muon spin rotation confirmed a magnetic ground state in both compounds, but also revealed for the stoichiometric material an ordering temperature much lower than any previously reported one. Along with the observed stabilization of magnetism in the electron-doped compound, this suggests that magnetism in the nominally undoped BaVS 3 is essentially an extrinsic property, possibly related to slight deviations from the stoichiometry, and that the perfectly pure material is non-magnetic.

SQUID magnetometry performed on the fullerene based charge transfer salt TDAE-C 60 shows the presence of a superconducting phase below T c = 17.4 K, coexisting with the already known magnetic phase. A large fraction Meissner effect ( f ≈ 0.3) appears only when the compound is slowly cooled across the temperatures corresponding to (partial) freezing of the molecular rotations. The ferromagnetic response prevails over the Meissner effect for H > 6 Oe. A strong diamagnetic contribution to the RF susceptibility, appearing below T c , confirms these findings. This phenomenon sheds new light on the complementary nature of super-conductivity and magnetism in low dimensional Mott-Hubbard systems.

Mn 1− x Fe x In 2 Se 4 compounds ( x =0.1; x =0.7) were grown by the chemical vapor transport method. X-ray diffraction analysis data show that these compositions crystallize as different polytypes that belong to the hexagonal structure. The crystal symmetry of the sample with x =0.1 belongs to the space group R 3 ¯ m and for the sample with x =0.7 the space group is P6 3 mc. The magnetic behavior of both samples has been investigated in the temperature range between 5 and 300 K. Spin-glass-like behavior below the freezing temperature T f =9 K has been found for the sample with x =0.7. The sample with Fe content x =0.1 behaves as a paramagnet down to the lowest experimental measured temperature. High-temperature susceptibility data follow the Curie–Weiss law with a negative paramagnetic temperature indicating predominant antiferromagnetic interactions. Optical studies reveal that both samples ( x =0.1; 0.7) are direct band gap semiconductors. The temperature dependence of the energy gap fits Varshni relation quite well.

We report on the synthesis and characterization of BiFe${}_{0.5}$Mn${}_{0.5}$O${}_{3}$, a potential type-I multiferroic compound displaying temperature-induced magnetization reversal. Bulk samples were obtained by means of solid-state reaction carried out under the application of hydrostatic pressure of 6 GPa at 1100 \ifmmode^\circ\else\textdegree\fi{}C. The crystal structure is a highly distorted perovskite with no cation order on the $B$ site, where, besides a complex scheme of tilt and rotations of the TM-O${}_{6}$ octahedra, large off-centering of the bismuth ions is detected. Below ${T}_{1}$ $=$ 420 K the compound undergoes a first weak ferromagnetic transition related to the ordering of iron-rich clusters. At lower temperatures (just below RT) a complex thermally activated mechanism induces at first an enhancement of the magnetization at ${T}_{2}$ $=$ 288 K, then a spontaneous reversal giving rise to a negative response. The complementary use of powder neutron diffraction, superconducting quantum interference device magnetometry, and M\"ossbauer spectroscopy allowed us to propose as a possible interpretation of the overall magnetic behavior the presence of an uncompensated competitive coupling between nonequivalent clusters of weakly ferromagnetic interactions characterized by different critical temperatures and resultant magnetizations.

The effects of sample resistivity on magnetocrystalline anisotropy field measurements in pulsed fields are studied. Computer programs have been developed for simulating a sinusoidal field penetration and exponential decrease into a long cylindrical sample (one dimension diffusion problem), for the case of linear and nonlinear magnetic field diffusion. Simulations of conducting samples show the dependence of the delay of field at different positions within the sample with respect to the sample resistivity. In magnetic samples the resistivity itself has various effects. The values of the magnetization curve in an increasing field are lower than that corresponding to a decreasing field (this shows a hysteretic behaviour), the magnetic field values are lower in the interior of the sample, the two peaks of the second derivation of the magnetization corresponding to the anisotropy field are shifted, the value of the obtained anisotropy is higher in the increasing field with respect to the decreasing one, while the true anisotropy value lies between those and closer to the peak found in the decreasing field. Experimental results obtained on a Co polycrystalline sample at 78 K are in qualitative agreement with the presented simulations. The optimization of the field rise time in anisotropy field measurements by singular point detection is discussed with respect to the sample resistivity.

The temperature dependence of the upper critical magnetic field ${\mathit{H}}_{\mathit{c}2}$ of the superconducting ${\mathrm{RbCs}}_{2}$${\mathrm{C}}_{60}$ fullerene has been obtained. The value of ${\mathit{H}}_{\mathit{c}2}$(0) at zero temperature is estimated to be 17 T and the coherence length \ensuremath{\xi}(0)=4.4 nm. The lower critical field ${\mathit{H}}_{\mathit{c}1}$ has been studied using three different methods. The ${\mathit{H}}_{\mathit{c}1}$(T) dependence obtained from the procedures based on the deviation from perfect diamagnetism and on Bean's critical-state model has a positive curvature with decreasing temperature. It is shown from a high-field analysis that this saturationless dependence does not reflect the intrinsic ${\mathit{H}}_{\mathit{c}1}$ of the superconductor. The value of ${\mathit{H}}_{\mathit{c}1}$(0) is estimated to be 5.5--8.1 mT and the penetration depth \ensuremath{\lambda}(0)=300--370 nm.

We have studied a magnet model for 100 T field generation formed by two single-layer concentric coils. They are made of soft material and are mechanically independent. The containment is given by high strength glass fiber composite jackets. The radial and longitudinal pressures on the wire are taken equal in order to keep in equilibrium the conductive turns (isostatic pressure).

By means of neutron powder diffraction, we investigated the effect of the polar Bi$^{3+}$ ion on the magnetic ordering of the Mn$^{3+}$ ions in BiMn$_3$Mn$_4$O$_{12}$, the counterpart with \textit{quadruple} perovskite structure of the \textit{simple} perovskite BiMnO$_3$. The data are consistent with a \textit{noncentrosymmetric} spacegroup $Im$ which contrasts the \textit{centrosymmetric} one $I2/m$ previously reported for the isovalent and isomorphic compound LaMn$_3$Mn$_4$O$_{12}$, which gives evidence of a Bi$^{3+}$-induced polarization of the lattice. At low temperature, the two Mn$^{3+}$ sublattices of the $A'$ and $B$ sites order antiferromagnetically (AFM) in an independent manner at 25 and 55 K, similarly to the case of LaMn$_3$Mn$_4$O$_{12}$. However, both magnetic structures of BiMn$_3$Mn$_4$O$_{12}$ radically differ from those of LaMn$_3$Mn$_4$O$_{12}$. In BiMn$_3$Mn$_4$O$_{12}$ the moments $\textbf{M}_{A'}$ of the $A'$ sites form an anti-body AFM structure, whilst the moments \textbf{M}$_{B}$ of the $B$ sites result from a large and \textit{uniform} modulation $\pm \textbf{M}_{B,b}$ along the b-axis of the moments \textbf{M}$_{B,ac}$ in the $ac$-plane. The modulation is strikingly correlated with the displacements of the Mn$^{3+}$ ions induced by the Bi$^{3+}$ ions. Our analysis unveils a strong magnetoelastic coupling between the internal strain created by the Bi$^{3+}$ ions and the moment of the Mn$^{3+}$ ions in the $B$ sites. This is ascribed to the high symmetry of the oxygen sites and to the absence of oxygen defects, two characteristics of quadruple perovskites not found in simple ones, which prevent the release of the Bi$^{3+}$-induced strain through distortions or disorder. This demonstrates the possibility of a large magnetoelectric coupling in proper ferroelectrics and suggests a novel concept of internal strain engineering for multiferroics design., 9 pages, 7 figures, 5 tables

We report the magnetic and magnetocaloric properties in Co-doped Ni–Mn–Ga Heusler alloys around the Mn-rich composition Ni 50 Mn 30 Ga 20 . The presence of Co affects profoundly the critical temperatures and alters the exchange interactions of martensite and austenite to different extents; by varying the composition it is possible to tune the critical temperatures and to induce a paramagnetic gap between the magnetically ordered martensite and magnetic austenite, thus giving rise to a reverse magnetostructural transformation. Contrary to the Co-free alloys, the saturation magnetization moment of austenite is strongly enhanced by Co with respect to the martensitic one: thus the magnetocaloric effect turns from direct into inverse. Remarkable values of the magnetic properties related to the magnetocaloric effect, e.g. the saturation magnetization jump at the transformation (Δ M ) and the field dependence of the transformation temperature ( dT / dH ) are reported, together with high positive values of the isothermal magnetic entropy change (Δ S ). The conditions for enhancing the magnetocaloric properties and triggering the sign reversal of the magnetocaloric effect are discussed.