Magnetic and nonmagnetic impurities in some A-15 structure systems. II. Magnetic properties

We present measurements of the susceptibility of the A-15 structure systems NbyPt_100–y–x M _x where M = Fe and Ru (y = 73–78). These measurements correlated with those of the critical temperature T _c permit us to conclude that there is a saturation of the effective number of magnetic impurity atoms and that these atoms are situated on the chains. We find also that the magnetic moment of the Fe atoms depend on the value of y. The high value of the Curie temperature and its variation is discussed with the aid of a model of pairs with antiferromagnetic interaction. In order to describe the formation of the localized moments we have taken into account the effect of the environment around each impurity. Depending on the number and the nature of the nearest neighboring atoms, we deduce a magnetic or nonmagnetic behavior of the impurity. The variation of the moment as a function of the nearest neighbors is explained by supposing electronic redistribution between the atoms, which is the same as supposing an interatomic charge transfer.     

Supercritical carbon dioxide extraction of polyunsaturated fatty acids from Northern shrimp (Pandalus borealis Kreyer) processing by-products

This study investigated the potential of Northern shrimp (Pandelus borealis Kreyer) by-products as a source of omega-3 polyunsaturated fatty acids (ω-3 PUFAs). The by-products (heads, shell and tail) of processing accounted for approximately 50–60% of the catch. Supercritical CO₂ extraction (SFE) of the by-products at 35 MPa and 40 °C generated a deep red oil, rich in ω-3 PUFAs, specifically 7.8 ± 0.06% eicosapentaenoic acid (EPA) and 8.0 ± 0.07 % docosahexaenoic acid (DHA).     

Magnetic susceptibility of (rare earth) x Mo6S8

We have studied the susceptibility of all (RE) _x Mo₆S₈ compounds between 1.3 and 300 K (RE = rare earth). In the two superconducting compounds Ho _1.2 Mo ₆ S ₈ and Dy _1.2 Mo₆S₈ magnetic ordering is expected in the temperature range 0.1–1 K. The magnetic transition in CeMo₆S₈ at2.25 K is of antiferromagnetic nature. A second anomaly at 1.6 K in this compound may announce a low-temperature ferromagnetic state.     

The behavior of magnetic and nonmagnetic impurities in the system Nb76Pt24−x Fe x

We find that Fe is magnetic when introduced as an impurity in the A-15 super-conductor Nb ₇₆ Pt ₂₄ . The ternary diagram of the system Nb-Pt-Fe is presented. The Fe impurities show a magnetic behavior when they are on the linear chains (Nb sites) and a nonmagnetic behavior when they are on the cubic sites (Pt sites). Supposing that the Fe atoms have a pair-breaking effect as well as a nonmagnetic effect on the superconducting state and determining the latter by adding nonmagnetic impurities (Ru), we are able to fit the measured critical field as a function of temperature to the WHH theory generalized to include magnetic impurities. The analysis shows that the exchange interactionJ between conduction electrons and the Fe atoms is negative. A Jaccarino-Peter compensation effect takes place at about 2 at % Fe. The inverse Fe susceptibility curves are fitted using a model of short-range interactions between impurities.     

Magnetic and nonmagnetic impurities in some A-15 structure systems. I. Superconducting properties

We present measurements of the critical temperature T _c and the critical field H _c2 of the A-15 structure systems Nb _y ,Pt_100–y–x M _x where M = Fe and Ru (y = 73–78). T _c is influenced by two effects: one due to the magnetic Fe atoms, which causes a strong decrease, and the other due to the nonmagnetic effect of the Fe atoms, which causes a smaller but non-negligible effect. For the study of the nonmagnetic effect we introduced Ru impurities instead of Fe. Anomalous high critical field values are found as T 0, and the curves H _c2 versus T do not follow the WHH theory generalized to include magnetic impurities. The introduction of an empirical parameter permits us to fit our experimental results. This abnormal behavior of H _c2 is discussed in terms of strong-coupling and anisotropy effects.