Thermal relaxation of magnetic clusters in amorphous Hf_{57}Fe_{43} alloy

The magnetization processes in binary magnetic/nonmagnetic amorphous alloy Hf_{57}Fe_{43} are investigated by the detailed measurements of magnetic hysteresis loops, temperature dependence of magnetization, relaxation of magnetization and magnetic ac susceptibility, including a nonlinear term. Blocking of magnetic moments at lower temperatures is accompanied with the slow relaxation of magnetization and magnetic hysteresis loops. All of the observed properties are explained with the superparamagnetic behaviour of the single domain magnetic clusters inside the nonmagnetic host, their blocking by the anisotropy barriers and thermal fluctuation over the barriers accompanied by relaxation of magnetization. From magnetic viscosity analysis based on thermal relaxation over the anisotropy barriers it is found out that magnetic clusters occupy the characteristic volume from 25 up to 200 nm3 . The validity of the superparamagnetic model of Hf_{57}Fe_{43} is based on the concentration of iron in the Hf_{100-x}Fe_{43} system that is just below the threshold for the long range magnetic ordering. This work throws more light on magnetic behaviour of other amorphous alloys, too

Vortex Motion Noise in Micrometre-Sized Thin Films of the Amorphous Nb0.7Ge0.3 Weak-Pinning Superconductor

We report high-resolution measurements of voltage (V) noise in the mixed state of micrometre-sized thin films of amorphous Nb0.7Ge0.3, which is a good representative of weak-pinning superconductors. There is a remarkable difference between the noise below and above the irreversibility field Birr. Below Birr, in the presence of measurable pinning, the noise at small applied currents resembles shot noise, and in the regime of flux flow at larger currents decreases with increasing voltage due to a progressive ordering of the vortex motion. At magnetic fields B between Birr and the upper critical field Bc2 flux flow is present already at vanishingly small currents. In this regime the noise scales with (1-B/Bc2)^2 V^2 and has a frequency (f) spectrum of 1/f type. We interpret this noise in terms of the properties of strongly driven depinned vortex systems at high vortex density.Comment: 8 pages, 5 figures, version accepted for publication in PR

Force distributions in a triangular lattice of rigid bars

We study the uniformly weighted ensemble of force balanced configurations on a triangular network of nontensile contact forces. For periodic boundary conditions corresponding to isotropic compressive stress, we find that the probability distribution for single-contact forces decays faster than exponentially. This super-exponential decay persists in lattices diluted to the rigidity percolation threshold. On the other hand, for anisotropic imposed stresses, a broader tail emerges in the force distribution, becoming a pure exponential in the limit of infinite lattice size and infinitely strong anisotropy.Comment: 11 pages, 17 figures Minor text revisions; added references and acknowledgmen

Transverse-mode & polarization characteristics of double-fused 1.52 μm vertical-cavity lasers

AbstractWe report on the transverse mode and polarization characteristics of a novel 1.52 μm vertical-cavity laser that utilizes an InGaAsP strain-compensated quantum-well active layer and two AIAs/GaAs quarter-wave mirrors. The 6 and 8 μm diameter devices exhibit room-temperature pulsed threshold currents as low as 4 mA, and a maximum output power of 14 mW was measured on a 60 μm diameter device

Experimental evidence of a fractal dissipative regime in high-T_c superconductors

We report on our experimental evidence of a substantial geometrical ingredient characterizing the problem of incipient dissipation in high-T_c superconductors(HTS): high-resolution studies of differential resistance-current characteristics in absence of magnetic field enabled us to identify and quantify the fractal dissipative regime inside which the actual current-carrying medium is an object of fractal geometry. The discovery of a fractal regime proves the reality and consistency of critical-phenomena scenario as a model for dissipation in inhomogeneous and disordered HTS, gives the experimentally-based value of the relevant finite-size scaling exponent and offers some interesting new guidelines to the problem of pairing mechanisms in HTS.Comment: 5 pages, 3 figures, RevTex; Accepted for publication in Physical Review B; (figures enlarged

Pojačanje zapinjanja magnetskih vrtloga u neutronima ozračenom supravodiču MgB2

m − H loops for virgin and neutron irradiated bulk and powder samples of MgB2 were measured in the temperature range 5 − 30 K in magnetic field B ≤ 1 T. The irradiation at thermal neutron fluences 9 · 1013 and 4.5 · 1014 cm−2 caused very small enhancement of m − H loops at lower temperatures (T < 20 K), whereas the effect at high temperatures was unclear due to the difficulty in achieving exactly the same measurement temperature prior and after irradiation. However, the irradiation at 4.5 · 1015 cm−2 produced clear enhancement of m − H loops (hence Jc) at all investigated temperatures, which provides the evidence for the enhancement of flux pinning in MgB2 due to ion tracks resulting from n+10B reaction. The potential of this technique for the enhancement of flux pinning in high temperature superconductors is briefly discussed.Ozračivanje termičkim neutronima do 9 · 1013 i 4.5 · 1014 n/cm2 uzrokovalo je vrlo malo proširenje m−H krivulja na nižim temperaturama (T < 20 K), dok je učinak na višim temperaturama nejasan zbog poteškoće da se postigne točna jednakost mjerne temperature prije i poslije ozračivanja. Ozračivanje na 4.5 · 1015 n/cm2 uzrokovalo je jasno proširenje m − H krivulja na svim temperaturama, što ukazuje da ionski tragovi nastali n+10B reakcijom pojačavaju zapinjanje linija magnetskog toka u MgB2. Kratko se razmatra prikladnost tog postupka za pojačanje zapinjanja linija toka u visokotemperaturnim supravodičima

Biotypes of Candida albicans isolated from clinical material of hospitalized patients

Metodom biotipizacije po Oddsu i Abbottu tipizirano je 910 izolata vrste Candida albicans iz uzoraka materijala različitih organskih sustava 360 hospitaliziranih bolesnika. Tipizacijom je dobiveno 79 biotipova, a 14 najučestalijih (355, 305, 345, 155, 357, 105, 315, 144, 157, 115, 057, 257, 300 i 244) činilo je 89,3 % svih biotipova ove vrste. Najučestaliji biotip bio je 355 i činio je 20,9 % svih biotipova vrste C. albicans iz svih uzoraka. Ovaj biotip bio je zastupljen s 36,2 % u izolatima iz kardiovaskularnog sustava, s 21,4 % u izolatima iz dišnog sustava, s 20,1 % u izolatima iz probavnog sustava, s 19,5 % u izolatima iz obrisaka kože, s 19,4 % u izolatima iz središnjeg živčanog sustava i sa 17,1 % u izolatima iz spolnomokraćnog sustava. Ova metoda biotipizacije pogodna je za epidemiološka istraživanja zastupljenosti biotipova vrste C. albicans, jer omogućava ispitivanje velikog broja izolata, a ne iziskuje velike materijalne troškove i skupu opremu.Using the Odds and Abbott method, 910 isolates of Candida albicans were typed. They were isolated from samples of different systems in 360 hospitalized patients. Typing revealed 79 biotypes where 14 (355, 305, 345, 155, 357, 105, 315, 144, 157, 115, 057, 257, 300 i 244) of them were the most common, accounted for 89.3 % of all biotypes. The most common biotype, 355, made up 20.9 % of all biotypes of this species isolated from all samples. It was present in 36.2 % of isolates from the cardiovascular system, 21.4 % of isolates from the respiratory system, 20.1 % of isolates from the gastrointestinal system, 19.5 % of isolates from the skin, 19.4 % of isolates from the central nervous system, and in 17.1 % of isolates from the urogenital system. This method is suitable for epidemiological research of the presence of C. albicans biotypes because it enables the testing of a large number of isolates with very low cost and reasonably simple equipment

Enhanced superconductivity in Hf-base metallic glasses

Systematic study of electrical resistivity of Hf_{100-x}Fe_x (x=20,25), Hf_{100-x}Cu_x (x=30,40,50), and Ti_{65}Cu_{35} metallic glasses has been done in the temperature range 0.3 K - 290 K, and in magnetic fields B <= 5 T. All Hf-base alloys are superconducting with T_c >= 0.44 K, which is well above T_c of pure crystalline Hf (0.13 K). From the initial slopes of the upper critical fields, (dH_{c2}/dT)_{T_c}, and resistivities we determined the dressed electronic densities of states, N_{\gamma}(E_F), for all alloys. Both T_c and N_{\gamma}(E_F) decrease with increasing x (Fe and Cu content). The results are compared with those for corresponding Zr-base metallic glasses and ion-implanted Hf films.Comment: 9 pages, 4 figures, 1 tabl