Thermal annealing of FePt thin films by millisecond plasma arc pulses

A series of 20 and 100 nm Fe₅₃Pt₄₇ thin films sputter-deposited onto Si substrates have been thermally annealed using a pulsed thermal plasma arc lamp. A series of one, three or five pulses were applied to the thin films with widths of either 50 or 100 ms. The microstructure and magnetic properties of these annealed Fe₅₃Pt₄₇ films are discussed according to the various annealing conditions and A1 to L1₀ phase transformation. Upon pulse annealing, the average in-plane grain size of 15 nm (nearly equivalent for both film thicknesses) was observed to increase to values near 20 nm. In general, increasing the pulse width or number of pulses increased the L1₀ order parameter, tetragonality of the c/a ratio and coercivity of the specimen. The exception to this trend was for five pulses at 100 ms for both film thicknesses, which indicated a reduction of the order parameter and coercivity. This reduction is believed to be a result of the interdiffusion of Fe and Pt into the Si substrate and the formation of iron oxide clusters in the grain boundaries characterized by atom probe tomography.     

Thermodynamics of CeAl2 at low temperatures: specific heat and spin-lattice relaxation rate

Thermodynamic calculations, developed here, show that a considerable fraction of the observed low-temperature nuclear spin-lattice relaxation rate and specific heat of CeAl₂-both varying linearly with temperature-may be due to the existence of new low-frequency features in the spin-excitation spectrum of incommensurate magnetic structures.     

Single particle excitations in Ba from a ( , t) reaction study

The ¹³⁰Ba( ¹²⁹Ba reaction was studied with 25 MeV deuterons and excellent energy resolution. About 50 excited states have been observed up to E_x = 2.0 MeV and for 42 of them transferred ℓ values and/or J^π values were assigned on the basis of the measured angular distributions and asymmetries. The level scheme of ¹²⁹Ba, the neutron pickup strength distribution and the known electromagnetic decay scheme are compared with results of calculations with the interacting boson-fermion model. These simple multi-shell IBFM-1 calculations describe well the main features of the experimental data.     

Transport and thermodynamic properties of CeAuAl3

We present measurements of the specific heat, the electrical resistivity, the Hall effect, and the magnetic susceptibility of CeAuAl₃, a new heavy-electron compound that crystallizes in an ordered derivative of the tetragonal BaAl₄-type structure. For comparison we have also done some of these measurements on the isostructural non-magnetic reference compound LaAuAl₃, which appears to be a simple metal. Below K, CeAuAl₃ orders antiferromagnetically and below 1K, we encounter Fermi liquid behaviour with considerably enhanced effective masses, i.e., a quadratic temperature dependence of the resistivity with a large prefactor and a sizable linear-in-T contribution to the specific heat. This linear-in-T contribution increases by more than a factor 50 from its value at to its value at . Consequently CeAuAl₃ develops a heavy-electron ground state, coexisting with antiferromagnetic order. The small energy scales involved in the problem make CeAuAl₃ a good candidate for tuning it, by varying external parameters, towards a quantum critical point. At high temperatures we observe local moment behaviour. From the temperature dependence of the magnetic susceptibility and the specific heat we have derived the crystalline-electric-field-split level scheme of the J =5/2 multiplet. Distinct features in the electrical resistivity provide additional evidence for this level splitting. Received: 6 November 1997 / Accepted: 17 November 1997     

Bioautographic Detection of Antimicrobial Compounds in the Edible Shiitake Mushroom (Lentinus edodes)

JPC – Journal of Planar Chromatography – Modern TLC - The shiitake mushroom is well known for its health-beneficial effects. In this study we examined its antimicrobial activity by use...     

Nonlinear dynamics of a Bose-Einstein condensate in a magnetic waveguide

We have studied the internal and external dynamics of a Bose-Einstein condensate in an anharmonic magnetic waveguide. An oscillating condensate experiences a strong coupling between the center of mass motion and the internal collective modes. Because of the anharmonicity of the magnetic potential, not only the center of mass motion shows harmonic frequency generation, but also the internal dynamics exhibit nonlinear frequency mixing. Thereby, the condensate shows shape oscillations with an extremely large change in the aspect ratio of up to a factor of 10. We describe the data with a theoretical model to high accuracy. For strong excitations we test the experimental data for indications of a chaotic behavior.     

Unusual magnetic-field-induced phase transition in the mixed state of superconducting NbSe2

The thermal conductivity kappa in the basal plane of single-crystalline hexagonal NbSe2 has been measured as a function of magnetic field H, oriented both along and perpendicular to the c axis, at several temperatures below T(c). With the magnetic field in the basal plane and oriented parallel to the heat flux we observed, in fields well below H(c2), an unexpected hysteretic behavior of kappa(H) with all the generic features of a first order phase transition. The transition is not manifest in the kappa(H) curves, if H is still in the basal plane but oriented perpendicularly to the heat-flux direction. The origin of the transition is not yet understood.     

Low-dimensional spin S = 1/2 system at the quantum critical limit: Na2V3O7

We report the results of measurements of the dc susceptibility and the 23Na-NMR response of Na2V3O7, a recently synthesized, nonmetallic low dimensional spin system. Our results indicate that, upon reducing the temperature to below 100 K, the V4+ moments are gradually quenched, leaving only one moment out of nine active. The NMR data reveal a phase transition at very low temperatures. With decreasing applied field H, the critical temperature shifts towards T=0 K, suggesting that Na2V3O7 may be regarded as an insulator reaching a quantum critical point at H=0.     

Universal impedance fluctuations in wave chaotic systems

We experimentally investigate theoretical predictions of universal impedance fluctuations in wave chaotic systems using a microwave analog of a quantum chaotic infinite square well potential. We emphasize the use of the radiation impedance to remove the nonuniversal effects of the particular coupling between the outside world and the scatterer. Specific predictions that we test include the probability density functions (PDFs) of the real and imaginary parts of the universal impedance, the equality of the variances of these PDFs, and the dependence of these PDFs on a single loss parameter.