Tuning structural and magnetic properties of Fe oxide nanoparticles by specific hydrogenation treatments.

Structural and magnetic properties of Fe oxide nanoparticles prepared by laser pyrolysis and annealed in high pressure hydrogen atmosphere were investigated. The annealing treatments were performed at 200 °C (sample A200C) and 300 °C (sample A300C). The as prepared sample, A, consists of nanoparticles with ~ 4 nm mean particle size and contains C (~ 11 at.%), Fe and O. The Fe/O ratio is between γ-Fe2O3 and Fe3O4 stoichiometric ratios. A change in the oxidation state, crystallinity and particle size is evidenced for the nanoparticles in sample A200C. The Fe oxide nanoparticles are completely reduced in sample A300C to α-Fe single phase. The blocking temperature increases from 106 K in A to 110 K in A200C and above room temperature in A300C, where strong inter-particle interactions are evidenced. Magnetic parameters, of interest for applications, have been considerably varied by the specific hydrogenation treatments, in direct connection to the induced specific changes of particle size, crystallinity and phase composition. For the A and A200C samples, a field cooling dependent unidirectional anisotropy was observed especially at low temperatures, supporting the presence of nanoparticles with core-shell-like structures. Surprisingly high MS values, almost 50% higher than for bulk metallic Fe, were evidenced in sample A300C.

Magnetic Phase Coexistence and Hard-Soft Exchange Coupling in FePt Nanocomposite Magnets.

With the aim of demonstrating phase coexistence of two magnetic phases in an intermediate annealing regime and obtaining highly coercive FePt nanocomposite magnets, two alloys of slightly off-equiatomic composition of a binary Fe-Pt system were prepared by dynamic rotation switching and ball milling. The alloys, with a composition Fe53Pt47 and Fe55Pt45, were subsequently annealed at 400 °C and 550 °C and structurally and magnetically characterized by means of X-ray diffraction, 57Fe Mössbauer spectrometry and Superconducting Quantum Interference Device (SQUID) magnetometry measurements. Gradual disorder-order phase transformation and temperature-dependent evolution of the phase structure were monitored using X-ray diffraction of synchrotron radiation. It was shown that for annealing temperatures as low as 400 °C, a predominant, highly ordered L10 phase is formed in both alloys, coexisting with a cubic L12 soft magnetic FePt phase. The coexistence of the two phases is evidenced through all the investigating techniques that we employed. SQUID magnetometry hysteresis loops of samples annealed at 400 °C exhibit inflection points that witness the coexistence of the soft and hard magnetic phases and high values of coercivity and remanence are obtained. For the samples annealed at 500 °C, the hysteresis loops are continuous, without inflection points, witnessing complete exchange coupling of the hard and soft magnetic phases and further enhancement of the coercive field. Maximum energy products comparable with values of current permanent magnets are found for both samples for annealing temperatures as low as 500 °C. These findings demonstrate an interesting method to obtain rare earth-free permanent nanocomposite magnets with hard-soft exchange-coupled magnetic phases.

Mn-Induced Thermal Stability of L10 Phase in Fept Magnetic Nanoscale Ribbons.

Magnetic nanoscale materials exhibiting the L10 tetragonal phase such as FePt or ternary alloys derived from FePt show most promising magnetic properties as a novel class of rare earth free permanent magnets with high operating temperature. A granular alloy derived from binary FePt with low Pt content and the addition of Mn with the nominal composition Fe57Mn8Pt35 has been synthesized in the shape of melt-spun ribbons and subsequently annealed at 600 °C and 700 °C for promoting the formation of single phase, L10 tetragonal, hard magnetic phase. Proton-induced X-ray emission spectroscopy PIXE has been utilized for checking the compositional effect of Mn addition. Structural properties were analyzed using X-ray diffraction and diffractograms were analyzed using full profile Rietveld-type analysis with MAUD (Materials Analysis Using Diffraction) software. By using temperature-dependent synchrotron X-ray diffraction, the disorder-order phase transformation and the stability of the hard magnetic L10 phase were monitored over a large temperature range (50-800 °C). A large interval of structural stability of the L10 phase was observed and this stability was interpreted in terms of higher ordering of the L10 phase promoted by the Mn addition. It was moreover found that both crystal growth and unit cell expansion are inhibited, up to the highest temperature investigated (800 °C), proving thus that the Mn addition stabilizes the formed L10 structure further. Magnetic hysteresis loops confirmed structural data, revealing a strong coercive field for a sample wherein single phase, hard, magnetic tetragonal L10 exists. These findings open good perspectives for use as nanocomposite, rare earth free magnets, working in extreme operation conditions.

Diagnosis of adult linear IgA dermatosis by immunoelectronmicroscopy in 16 patients with linear IgA deposits.

Homogeneous linear IgA deposits at the dermo-epidermal junction (DEJ) shown by direct immunofluorescence are characteristic of what is termed linear IgA bullous dermatosis. However, it is not yet certain that this disease constitutes an entity distinct from other subepidermal blistering diseases, especially when IgG deposits are also present. Sixty-one cases of subepidermal blistering disease in adults were therefore investigated by immunoelectron microscopy (IEM), and the 16 patients observed to have homogeneous linear IgA deposits were compared with the 45 who had no IgA but had IgG and/or C3. In 11 of the 16 patients with IgA (four of whom also had IgG), the deposits were linear and formed a mirror image pattern on each side of the lamina densa from which they were separated by a clear space. In contrast to this monomorphic IEM pattern, clinical and other laboratory findings were very heterogeneous, making exact clinical diagnosis difficult. Of the remaining five patients in this group of sixteen, three (all with both IgA and IgG) had bullous pemphigoid, epidermolysis bullosa acquisita, and cicatricial pemphigoid, respectively, on IEM and clinical investigation. In the remaining two patients (one with both IgA and IgG, and one with IgA only) the deposits were located in the lamina lucida, making precise classification impossible. None of the 45 patients with isolated IgG and/or C3 deposition displayed the mirror image pattern. We conclude that this IEM pattern may constitute a specific diagnostic criterion of linear IgA dermatosis.

[Penicillamine in 1985]. / Pénicillamine 1985.

After reviewing the history of the discovery of the action of D-penicillamine in rheumatoid arthritis, the authors define the practical modalities for the management of treatment based on their own experience and on the data from the literature. The therapeutic score remains relatively low because of the frequency of side effects and therapeutic escapes, even when an encouraging result has been obtained during the first years of treatment.

[Study of optimal posology of penicillamine in the treatment of common rheumatoid polyarthritis (apropos of a personal series of 200 cases)]. / Recherche d'une posologie optimale de la pénicillamine dans le traitement de la polyarthrite rhumatoïde commune. A propos d'une série personnelle de 200 cas.

A comparison of two series of patients with rhe,matic polyarthritis, the one (n = 140) treated with dosage equal to or higher than 900 mg, the other (n = 60) with dosage between 600 and 750 mg, did not reveal significant difference in clinical and biological efficacy. The number of side-effects was not significantly reduced by lower dosage, except for digestive tract disorders. A reduction of dosage does, therefore, not permit less strict supervision and monitoring for side-effects of treatment.