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.

Novel gas-stabilized iron clusters: synthesis, structure and magnetic behaviour.

A novel method for the synthesis of nanostructured films produced by depositing gas-phase magnetic nanoparticles is presented and the properties of the films are reported. The technique mixes metal vapour and small argon clusters produced in a supersonic expansion. The condensed clusters are subsequently deposited in situ onto copper grids. The cluster size is controlled by the vapour pressure of the metal inside the pick-up chamber. Detailed analysis of the transmission electron micrographs of the Fe clusters shows that there is a simple linear relationship between the average metal cluster diameter and the metal vapour pressure during deposition. Furthermore, the nanoparticles show a relatively narrow size distribution for a given set of experimental conditions. Structural and magnetic investigations have been performed on Fe cluster samples, and the influence of the metal vapour pressure has been studied. Detailed analysis of the magnetic and structural data has been performed and valuable information such as cluster size distributions, strength of the interparticle dipolar interactions and average magnetic moment per cluster are derived. It is shown that, at room temperature, the magnetic behaviour of the films is consistent with nanoparticle supermoments interacting via dipolar interactions.

[Management of hypertension and obesity: the observatory of management of uncontrolled hypertensives with respect to the presence or absence of overweight (PHYSIObs)]. / Prise en charge de l'hypertension artérielle et surcharge pondérale Observatoire de la prise en charge de patients hypertendus non contrôlés en fonction de la présence ou non d'un surpoids (PHYSIObs).

The object of this study was to compare the management of uncontrolled hypertensives (BP > 140/90 mmHg) by general practitioners with respect to the presence or absence of overweight (BMI > or =25 Kg/m2). A 2/1 stratification allowed comparison of 4080 patients who were overweight and 1951 patients with a normal body weight (normal BMI < 25 Kg/m2). The BP of patients who were overweight (> or =25 Kg/m2) was slightly higher than those with a normal BMI (161 +/- 12 mmHg vs. 159 +/- 12 mmHg, p < 0.001). The presence of a metabolic syndrome (43% vs. 7%, ATPIII criteria) was, logically, commoner in the patients overweight. However, the practitioners only recognised the presence of a metabolic syndrome in 65% of the overweight patients (28% true positives and 37% true negatives). The practitioners fixed their target value of systolic BP at 136.5 +/- 5.6 mmHg, in accordance with the recent recommendations of the Health Authorities. The targets were judged to be difficult to obtain in 18% of the overweight group and in 5% of patients with normal body weights. This optimism contrasted with the prescriptions, especially in the overweight patients, 46% of whom were treated by monotherapy and who remained for 44% on monotherapy at the end of the consultation. This descriptive study confirms the lack of awareness of the metabolic syndrome in overweight patients and identifies barriers to effective management of the hypertension of these high risk patients.