A neutron study of the antiferromagnetic order in CrSi alloys

Neutron diffraction measurements were made on polycrystalline CrSi alloys containing 0.90, 1.37, 1.85 and 2.74 at.% Si to establish the types of antiferromagnetic order in this system. The results show that three types of antiferromagnetic order occur in this concentration range. Below 1 at.% Si the behavior is similar to that of pure Cr with a transversely polarized spin density wave at high temperatures and a spin-flip to longitudinal polarization at low temperatures. Above 1.8 at.% Si only the commensurate structure develops while both the commensurate and incommensurate structures occur in the intermediate concentrations. The magnitude of the modulation wave vectors and also the average moments increase with increasing Si content. Within the rigid-band extension of the Fermi surface “nesting” model of Cr this implies that Si behaves as an electron donor in Cr.     

Decay of a new isotope, 24Si: A test of the isobaric multiplet mass equation

Observation of beta-delayed protons from the decay of the mass separated T_z=?2 nuclide ${}^{24}\text{Si}\text{(t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{≈100}\text{ms}\text{)}$ establishes the mass excess of the lowest T=2 (0⁺) state in ²⁴Al (5903±9 KeV). An excellent fit to the quadratic form of the isobaric multiplet mass equation is obtained.     

Low birefringence depressed cladding photosensitive fiber

The highly Ge-doped photosensitive fiber （PSF） has been widely used in the fabrication of fiber Bragg gratings （FBGs）. Its birefringence and cladding mode coupling characteristics greatly influence FBG＇s transmission feature in communication application areas. In this work, a new concept of the PSF is introduced which, along with an optimized birefringence design, a precisely controlled fabrication process, and a cladding mode depressed design, results in a written FBG with -25-dB clad mode-depressed ratio and a polarization mode dispersion value less than 0.045 ps.     

A multiple approach to the determination of radon fluxes from sediments

Determination of sedimentary fluxes of²²²Rn via diffusion was required as an input for a mass balance model of radon in a freshwater lake. We obtained these fluxes by: (1) direct measurement in the laboratory using a simulated sediment bed and water column; (2) a “sediment equilibration” technique; and (3) porewater modeling. The first method, analogous to an in situ benthic chamber approach, uses direct observation of the increasing²²²Rn activity in water overlying a sediment bed packed in plastic columns. This allows one to directly measure the fluxes and determine the effective wet bulk sediment diffusion coefficient (D _s). Radon flux estimates using these three techniques agreed to within approximately 10–15%.     

Examination of hard segment and soft segment phase separation in polyurethane medical materials by electron microscopy techniques.

A combination of transmission electron microscopy (TEM) and in situ tensile testing in an environmental scanning electron microscopy (ESEM) was used to evaluate the static bulk and dynamic surface morphologies of medical polyurethanes. TEM results showed phase-separated hard segment and soft segment structures. Surface morphology as a function of strain was studied using ESEM in conjunction with a tensometer.     

Low-temperature phase and magnetic interactions in FCC Fe-Cr-Ni alloys

The low-temperature (5 K < T < 300 K) magnetic properties of a set of nine isostructural fcc Fe-Cr-Ni (Fe ≈ 68 at %, Cr ≈ 20 at%, Ni ≈ 9 at%) alloys were studied by SQUID magnetometry, neutron diffraction and ultrasonic techniques. Type-1 antiferromagnetic (AF) ordering was observed below the Néel temperature, T_N. The dc susceptibility, χ(T), did not exhibit a simple Curie-Weiss dependence. Above T_N, atemperature independent component χ₀ was observed, i.e., χ(T) = χ₀ + C / (itT + θ. T_N was systematically influenced by the lattice parameter, a, decreasing from (47.9 ± 0.5) K to (35.0 ± 0.5) K as a increased by only 0.25%. The average magnetic moment of ≈ 0.6μ_B obtained from neutron scattering was lower than the ≈ 1 μ_B obtained from the SQUID data. Mean field estimates of antiferromagnetic nearest-neighbors exchange interaction (J₁) and ferromagnetic second-nearest-neighbors interaction (J₂) indicate that |J₂/J₁|≈ 1.5. We believe that this is evidence of the RKKY interaction, and self-consistently argue that only the external d electrons are responsible for the localized average moment. This may mean that s-d hybridization of the external electrons is weak in these alloys.