Perturbed-angular-correlation analysis of the magnetic state in the pseudo-binary system U(IN1-XSNX)(3)

We report on hyperfine interaction parameters at Cd-111 in U(In1-xSnx)(5) measured as a function of x concentration and temperature. We conclude that the valence difference between indium and tin in the pseudo-binary compounds is not larger than 0.2. At lower temperature we observe between x = 0 and x = 0.3 a reorientation of the magnetic structure

Dynamic spin correlations in U(In1-xSnx)(3) heavy-fermion compounds: a perturbed angular correlation study

By applying perturbed angular-correlation spectroscopy we have investigated spin correlations in the "heavy-fermion" compounds U(In1-xSnx)(3), with x=1.0, 0.7, and 0.5, by measuring the induced magnetic hyperfine field B-ind at diamagnetic Cd-111 probe nuclei as a function of temperature and applied magnetic field. In zero applied field, the absence of any detectable magnetic hyperfine field at Cd reveals the absence of static magnetic correlations down to 4.2 K. However, from the field dependence of B-ind we find evidence for the presence of field-induced, short-ranged, and dynamic spin correlation between U f electrons at all compositions. The strength and dynamics of these correlated spins strongly depend on x, temperature, and applied magnetic field. As an important feature, for compositions near x = 0.5, classified as a heavy-fermion material with electronic specific heat coefficient gamma = 500 mJ/mol K-2, these U spin correlations seem to set in from a relatively high temperature (greater than or equal to 37 K), and become very large on lowering temperature and/or increasing magnetic field, reflected in the measured Knight shift value K of about -32% at 4.2 K and B-app = 7 T. We believe that these short-range spin correlations and their relaxation dynamics are responsible for the low temperature increase in magnetic susceptibility and electronic specific heat, previously considered to be an indication of heavy-fermion behavior in this system

[Occupational asthma caused by a coloring reagent]

A ease of occupational asthma associated with rhinitis and conjunctivitis occurred in a patient,working in a textile factory and exposed to different coloring reagents is reported Symptoms appeared in phases correlated with changes in the use of the coloring reagents. Prick tests,were carried out with the different coloring reagents and,were positive for the yellow color. The test was followed by a clear increase in bronchial hyperreactivity to methacholine. Some individual preventive measures, such as wearing a face mask, led to reduction then disappearence of the symptoms

Neutron diffraction study of the magnetic ordering in NpBi

The magnetic ordering of NpBi has been determined by neutron diffraction on a single crystal. NpBi orders antiferromagnetically in the triple-k type-I structure (k=‖0 01‖,mk//k) below TN=192.5K. The ordered magnetic moment develops at TN with a critical exponent β=0.31±0.02 an increases continuosly on cooling to reach a value of 2.48μB/Np at low temperature

Magnetic excitations in NpBi

Proceedings of the First European Conference on Neutron ScatteringInternational audienceWe report inelastic neutron scattering measurements on a single crystal of NpBi. The observed magnetic excitation spectrum has two branches: one with longitudinal and the other with transverse polarisation. This is in agreement with the prediction of Jensen and Bak concerning the magnetic excitations in the triple-k type-I structure

A single-crystal magnetization and neutron scattering investigation of the magnetic structure of U₂Rh₂Sn

U₂Rh₂Sn is a member of a large family of intermetallic compounds with the tetragonal crystal structure. It orders antiferromagnetically at with the propagation vector k = (0,0,1/2). We have performed magnetization and neutron scattering experiments on a single crystal that show that the uranium atoms order in the collinear irreducible representation of the magnetic group, with the moments aligned parallel to the unique tetragonal axis. The value of the ordered magnetic moment of the uranium atoms refined from the neutron scattering intensities is . This is considerably reduced from the free-ion value for both and configurations and suggests that the f electrons are strongly hybridized with the conduction band

Magnetic structure and properties of NpS and NpSe

Single crystal neutron diffraction measurements on NpS and NpSe show that both compounds order AF at TN = 23 and 38 K, respectively, with a type II multi-k structure leading to non-equivalent Np sites, as shown by Mössbauer results

Magnetic properties of single crystalline NpAs-NpSe mixed compounds

The antiferromagnetic 3k-structure of NpAs transformes to a ferrimagnetic one in magnetic fields <60 kOe. The magnetic moment of the Np ion as determined by neutrons is 2.5μB. NpSe becomes antiferromagnetic below 38 K with a not yet resolved magnetic structure. The moment is only 1.35μB. In samples of NpAs mixed with 5, 10 and 15% NpSe we observed ferrimagnetic structures. The structure of the 5% sample was determined using neutrons and is described in detail. Admixture of NpSe increases the ferromagnetic exchange forces and reduces the ionic magnetic moment. The moment reduction is clearly evidenced by Mössbauer experiments. The exchange forces are anisotropic. Antiferromagnetic exchange favours the 〈100〉 direction, ferromagnetic exchange aligns the spins along 〈111

The reproductive cycle of the sea urchin Arbacia lixula in northwest mediterranean: potential influence of temperature and photoperiod

We studied the reproductive cycle of the sea urchin Arbacia lixula in a subtidal population from northeast Spain over four years using a gonadosomatic index (GSI) and gonad histology. Our results show that the GSI of A. lixula follows a seasonal cycle which peaks in May-July and attains its lowest values in October-November every year. The time course of the GSI matched closely the photoperiod cycle. We also found a remarkable inter-annual variability in the maximum value of GSI, which correlated with mean water temperature during the gonad growth period (winter and spring). Gonad histology was also in agreement with a single gametogenic cycle per year in this species. We explored the application of circular statistics to present and analyse gonadal development data, which allowed us to adequately handle the high intra-individual variability detected, with several developmental stages commonly found within the same gonad. The picture that emerged is one of a gametogenic timing driven by photoperiod, while the amount of reproductive output is determined by temperature. This is coherent with the tropical origin of the species and lends support to recent warnings about an increase in the abundance of this species in the Mediterranean as a result of global warming, with associated increased impact potential in sublittoral communities