Transport and Spectral Properties of Taylor-phase T-Al73Mn27 Complex Intermetallic

We report the experimental results for the electrical conductivity and the thermoelectric power of the complex intermetallic polygrain compound T-Al73Mn27. The electrical conductivity shows the non-metallic behavior, but with finite value in the T = 0 limit, and with unusual √T term appearing at the low temperature. This indicates the existence of an electronic pseudo-gap in the system, whereas more detailed theoretical analysis reveals a non-analytic behavior of the spectral conductivity function in the vicinity of the Fermi energy.</p

Hall Coefficient of the Y-Al-Ni-Co Decagonal Approximant

We have investigated anisotropic Hall coefficient of Y-Al-Ni-Co decagonal approximant of the Al76Co22Ni2 composition. The crystalline-direction-dependent studies were performed along three orthogonal directions a*, b and c of the Y-Al-Ni-Co unit cell, where (a,c) monoclinic atomic planes are stacked along the perpendicular b direction. Hall coefficient RH exhibits pronounced anisotropy, while at the same time the magnetic field in a given crystalline direction yields the same RH for the current along the other two crystalline directions in the perpendicular plane. The observed anisotropy is studied in terms of the anisotropic structure of the Y-Al-Ni-Co phase and Fermi surface. The results are compared to the anisotropy of the Hall coefficient of the d-Al-Ni-Co decagonal quasicrystal reported in literature.</p

Kaotični režim za radon u atmosferi i tlu

Radon concentrations were continuously measured outdoors, in a basement and in soil. The readings were made every 10 minutes and the series of records were analyzed to extract phase-space dynamical information. The application of fractal methods allowed exploration of the chaotic nature of radon in the atmosphere and soil. The computed fractal dimensions, such as the Hurst exponent (H) from the rescaled-range analysis, Lyapunov exponent (λ) and attractor dimension, provided estimates of the degree of chaotic behaviour. The obtained low values of the Hurst exponent (0 < H < 0.5) indicate anti-persistent behaviour (non-random changes) of the series, but the positive values of λ have pointed out a great sensitivity to initial conditions and the deterministic chaos that appeared in the variations of the radon concentrations. The calculated fractal dimensions of attractors indicate strong influence of meteorological parameters on radon in the atmosphere and soil.Mjerili smo koncentracije radona u otvorenoj atmosferi, u podrumu i u tlu, neprekidno tijekom mjesec dana u 10-minutnim intervalima. Radonske vremenske nizove analizirali smo usporedbom algoritama kako bi se dobile dinamičke informacije o faznom prostoru. Primjena fraktalnih metoda omogućila je ispitivanje kaotične prirode radona u atmosferi i tlu. Izračunate fraktalne dimenzije, kao što su Hurstov eksponent (H), Ljapunovljev eksponent (λ) i dimenzija atraktora, omogućile su procjenu stupnja kaotičnosti. Dobivene niske vrijednosti Hurstovog eksponenta (0 < H < 0, 5) ukazale su na antiperzistentno ponašanje vremenskih nizova (nenasumičnost promjena), dok su pozitivne vrijednosti pokazale veliku osjetljivost na početne uvjete i ukazale na deterministički kaos koji se pojavljuje u vremenskim varijacijama radona. Izračunate fraktalne dimenzije atraktora ukazale su na više (meteoroloških) parametara koji su utjecali na razine radona u atmosferi i u zemnom plinu

Heat Conduction in Complex Metallic Alloys

Thermal conductivity, κ, of ε-phase Al73Pd25Fe2 and "Bergman phase" Mg-Al-Zn is presented, which resembles the features common to all complex metallic alloys: relatively low value, shallow local maximum or change of slope at approximately 50 K, and a rise above 100 K. The electron contribution, κel, is calculated using Wiedemann-Franz law, while the calculation of the phonon thermal conductivity, κph, below 50 K is calculated employing Debye model. The sum of the two does not explain the experimental data at higher temperatures (above 100 K). This discrepancy is analyzed in three competitive ways: assuming an increase of an effective Lorenz number, taking into account the hopping of localized lattice vibrations, and employing a "bipolar diffusion effect", known from the theory of semiconductors. While the results of the former two approaches confirm other findings in literature, "bipolar diffusion effect" needs to be adopted for the specific electron structure of complex metallic alloys.</p

The origin of the surface field enhanced coercive field in nanophase Fe_73.5Cu_1Nb_3Si_15.5B_7 ribbon

The influence of surface fields H_p (generated with either direct or alternating core-current) on soft magnetic properties of amorphous and nanocrystalline Fe_73.5Cu_1Nb_3Si_15.5B_7 ribbon has been studied. While in amorphous ribbon the coercive field H_c decreases with H_p, in the same optimally annealed ribbon (H_c = 1.3 A/m, M_m ≈ M_s) H_c increases with H_p and the hysteresis loss E decreases with H_p for all explored types of H_p (static and dynamic with different phases with respect to that of the magnetizing field H). The unexpected increase of H_c in nanocrystalline ribbon is associated to the influence of H_p on the surface and main (inner) domain structure. The model is developed which takes into account this interaction and explains all experimental results. The probable adverse effect of the external fields with configurations similar to those of H_p on the performance of such ribbons is briefly discussed and some procedures which can prevent these effects are proposed

Hall Effect of the Triclinic Al73Mn27 and T-Al73Mn27–xPdx (0 ≤ x ≤ 6) Complex Metallic Alloys

The Hall coefficient, RH, of the triclinic Al73Mn27 and Taylor-phase Al73Mn27xPdx (x = 0, 2, 4 and 6) complex metallic alloys has been measured from 90 to 400 K. The Hall coefficients of all the samples are positive and they decrease strongly with the increase of temperature, T. For the separation of the normal, R0, and anomalous, RS, Hall coefficient the results for the paramagnetic susceptibility,χ(T), and electrical resistivity, ρ(T), have been used. The well defined linearity of the RH vs. χ(T)·ρ2(T) plots confirms the assumption that in these materials RH is dominated by spin-orbit interaction. The values deduced from the RH vs. χ and RH vs. χ·ρ2 plots in T­AlMnPd phases, fall between –2 × 10–10 m3 C–1 and 0 for R0, and are about 5 × 10–7 m3 C–1 for RS. The values deduced from the RH vs. χ·ρ2 plots in the triclinic Al73Mn27 alloy are about –15 × 10–10 m3 C–1 for R0, and about 1.5 × 10–5 m3 C–1 for RS.</p

Potencijalna korist od retrospektivne uporabe neutronskih monitora u svrhu bolje procjene izloženosti ionizirajućem zračenju na međunarodnim letovima – pitanja proizašla iz mjerenja pasivnim neutronskim dozimetrom i simulacije softverom EPCARD tijekom naglih promjena u solarnoj aktivnosti

Since air transport became more accessible, more and more people have been exposed to ionising radiation of cosmic origin. Measuring the neutron dose equivalent is a good approximation of total ambient dose equivalent, as neutrons carry about 50 % of the dose at flight altitudes. The aim of our study was to compare our measurements of the neutron component of secondary cosmic radiation dose, taken with passive dosimeters, with the data obtained from a simulation generated by EPCARD software, which is common in assessing flight crew exposure to ionising radiation. We observed deviations (both above and below) from the expected proportion of the neutron component (between 40 and 80 %), which pointed to certain issues with actual passive dosimeter measurement and the EPCARD simulation. The main limitation of the dosimeter are large uncertainties in high energy neutron response, which may result in underestimation of neutron dose equivalent. The main drawback of the software simulation is monthly averaging of solar potential in calculations, which can neglect sporadic high energy events. Since airlines worldwide almost exclusively use software (due to costs and convenience) to estimate the dose received by their crew, it is advisable to retrospectively recalculate the dose taking into account neutron monitor readings when solar activity changes.Budući da je zračni promet postao dostupniji, sve je više ljudi izloženo ionizirajućem zračenju kozmičkoga podrijetla. Neutronska komponenta sekundarnoga kozmičkog zračenja mjerena je pasivnim dozimetrom koji se sastoji od čvrstog detektora nuklearnih tragova i konvertera. Dobiveni rezultati uspoređeni su s podatcima dobivenima simulacijskim softverom EPCARD. Mjerenje neutronskoga doznog ekvivalenta na zrakoplovnim visinama dobra je aproksimacija ukupnog ambijentalnog doznog ekvivalenta, jer na zrakoplovnim visinama neutroni pridonose s oko 50 % doze. Međutim, uočena su određena odstupanja (i iznad i ispod) ove vrijednosti zbog varijacija u Sunčevoj aktivnosti. Ta su odstupanja očita kada se usporede izmjereni neutronski dozni ekvivalent i ukupni ambijentalni dozni ekvivalent dobiven simulacijom. Glavno ograničenje dozimetra velika je nesigurnost u području visokoenergetskih neutrona, što može rezultirati podcjenjivanjem neutronskoga doznog ekvivalenta. Glavni je nedostatak softverske simulacije u korištenju prosječnoga mjesečnog solarnog potencijala u proračunima, zbog čega se utjecaj sporadičnih visokoenergetskih događaja može previdjeti. Budući da se zrakoplovne tvrtke diljem svijeta gotovo isključivo koriste softverom za procjenu doze koju prima njihova posada (zbog troškova i jednostavnosti), preporučljivo je u slučaju promjene u Sunčevoj aktivnosti retrospektivno preračunati dozu

Anisotropic Transport Properties of the Orthorhombic Al13Co4 Approximant to the Decagonal Quasicrystal

Anisotropic transport properties (electrical resistivity, thermoelectric power, Hall coefficient and thermal conductivity) of the o-Al13Co4 orthorhombic approximant to the decagonal phase were investigated. The crystalline-direction-dependent measurements were performed along the a, b and c directions of the orthorhombic unit cell, where (b, c) atomic planes are stacked along the perpendicular a direction. Anisotropic electrical and thermal conductivities are the highest along the stacking a direction. The anisotropic thermoelectric power changes sign with the crystalline direction and so does the anisotropic Hall coefficient, which changes from the negative electron-like to the positive hole-like for different combinations of the electric current and magnetic field direction. The transport properties of the o-Al13Co4 phase were compared to the literature data on approximant to the decagonal quasicrystals, the Al76Co22Ni2 and the Al80Cr15Fe5, allowing for the study of evolution of transport properties with increasing structural complexity and unit cell size.</p

Nastanak koercitivnog polja pojačanog površinskim poljem u nanofaznoj traci fe73.5cu1nb3si15.5b7

The influence of surface fields Hp (generated with either direct or alternating core-current) on soft magnetic properties of amorphous and nanocrystalline Fe73.5Cu1Nb3Si15.5B7 ribbon has been studied. While in amorphous ribbon the coercive field Hc decreases with Hp, in the same optimally annealed ribbon (Hc = 1.3 A/m, Mm ≈ Ms) Hc increases with Hp and the hysteresis loss E decreases with Hp for all explored types of Hp (static and dynamic with different phases with respect to that of the magnetizing field H). The unexpected increase of Hc in nanocrystalline ribbon is associated to the influence of Hp on the surface and main (inner) domain structure. The model is developed which takes into account this interaction and explains all experimental results. The probable adverse effect of the external fields with configurations similar to those of Hp on the performance of such ribbons is briefly discussed and some procedures which can prevent these effects are proposed.Proučavali smo utjecaj površinskih polja Hp (proizvedenih stalnom ili izmjeničnom strujom sredice) na meka magnetska svojstva amorfne i nanokristalinične trake Fe73.5Cu1Nb3Si15.5B7. Dok se koercitivno polje Hc u amorfonj traci smanjuje s Hp, u toj traci nakon najpovoljnijeg opuštanja (Hc = 1.3 A/m, Mm ≈ Ms) Hc raste s Hp, a gubici E zbog histerezne petlje smanjuju se s Hp za različita polja Hp (statičko, i dinamičko s različitim fazama u odnosu na magnetizirajuće polje H). Neočekivan porast Hc u nanokristalnoj traci povezuje se s utjecajem Hp na površinsku i osnovnu (unutarnju) domensku strukturu. Razvili smo model koji uključuje to međudjelovanje i objašnjava sve eksperimentalne rezultate. Raspravljamo moguće nepovoljne utjecaje vanjskih polja slične konfiguracije kao Hp na svojstva tih traka i predlažemo načine spriječavanja tih utjecaja