Giant Moment, Superparamagnetic, Spin-Glass, and Quasiferromagnetic Properties of Dilute Pt?Fe Alloys

Using an RF-SQUID magnetometer, the temperature-dependent magnetic susceptibility of dilute Pt-Fe alloys containing 10.5 ppm Fe, and 0.87 and 0.99 at% Fe is measured in the temperature range 1 to 4.2 K and in de-fields between 0.5 and 15 Oe. For 10.5 ppm Fe, the susceptibility obeys the Curie law, and the saturation magnetic moment µsat is ? 9.3µB/Fe. The Pt-0.87 at% Fe and -0.99 at% Fe alloys are spin-glass and quasiferromagnetic, respectively, and both show superparamagnetic properties at temperatures between transition temperature Tt and ? 2Tt. Furthermore, the susceptibility of these alloys, around and below Tt, is field dependent, decreasing in magnitude with increasing field. Copyright © 1985 WILEY-VCH Verlag GmbH & Co. KGa

A one-dimensional model for nonexponential relaxation in a spin glass or glassy system

In this research, we have presented the phase space of the so-called spin glass or glassy systems with a one-dimensional randomly-oriented diode network (RODN) in which the bonds between the lattice points are represented with diodes and these diodes are assumed to be fully conducting in the forward biased direction, whereas they are assumed to have some constraints, in the reverse direction, depending on the temperature and/or some other external effects. Thus, a particle's conduction (or transition) probability in the reverse direction through a diode like bond, pr, can be assumed to have values between zero and one. By employing the Monte Carlo simulation technique to the diffusion of particles through this network we have explored the relaxation mechanism, and their functional forms. Our simulation data indicates that for reverse transition probability values of pr = 1.0 and 0.9, the time dependence of the relaxation data is exponential, on the other hand for pr < 0.2 it may be represented by either power or logarithmic time dependence. However, in general, our data can be represented by a stretched exponential time dependence, exp(-(t/?)?), especially in the limit of long t. Here the exponent ? has values in the range of 0.3 ? ? ? 1. For ? ? 1, obviously, exponential time dependence is regained. The value of ? ? 0.3, obtained for pr › 0, is very interesting, since it is almost the same as the critical exponent, 1/3, reported in the literature for the lowest occupation probability of site points spanning percolation clusters

Influence of lithium-holmium co-doped on structural and electrical properties of BSCCO superconductor

Bi2Pb0.5Sr2Ca4Cu 6LixHoxOy (0.0?x?0.5) samples were prepared by doping with Li and Ho at changing ratios and using meltquenching method. Thus, the influences of different doping levels of Li and Ho on the structural and electrical properties of the BPSCCO compound have been investigated by electrical resistivity, Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Energy Dispersive X-Ray Spectroscopy (EDX) techniques. It has been observed that, with increasing Li and Ho doping, the high-Tc Bi-(2223) phase gradually transforms into the low-T c Bi-(2212) and Bi-(2201) phases. However, It should be pointed out that these low-Tc superconducting phases are formed at all the doping levels, but increasing amount with increasing concentration of Li and Ho. Therefore, while the electrical resistivities in the normal states increase, the superconducting transition temperatures, Tc, hole concentrations, p, and the magnitudes of thermoelectric powers of all the samples decrease with increasing Li and Ho concentration x. As a result, the results suggest that with the increase in Li and Ho amount the superconductivities of all the samples are suppressed due to the destruction of the phase coherence by pair-breaking effects, or, to the hole filling mechanism with increasing x

Experimental and theoretical temperature distributions in a solar pond

In this study, an experimental and theoretical investigation of temperature distributions in an insulated solar pond, particularly during daytimes and nighttimes, is presented. Several temperature sensors connected to a data acquisition are placed vertically inside and the bottom of the pond and also horizontally and vertically in the insulated side walls, and used to measure temperature changes with time and position. In addition, we model the solar pond to compute theoretical temperature distributions and compare with the experimental measurements, and hence a good agreement is found between experimental and theoretical temperature profiles. There is a large amount of heat losses between daytimes and nighttimes, depending upon the temperature difference, and these present a significant potential for energy savings and storage. During the months of January, May and August, it is found that the total heat losses from the inner surface of the pond and its bottom and side walls, as a function of temperature difference, are determined to account for 227.76 MJ (e.g., 84.94% from the inner surface, 3.93% from the bottom and 11.13% from the side walls, respectively). © 2005 Elsevier Ltd. All rights reserved.University of Ontario Institute of Technology Natural Sciences and Engineering Research Council of CanadaThe authors acknowledge the support provided by Cukurova University in Turkey, and University of Ontario Institute of Technology and the Natural Sciences and Engineering Research Council of Canada in Canada

DC magnetic properties of the Ho doped ZnO compounds

In this work, we report on the DC magnetic properties of Ho doped ZnO, Zn0.8-4x Ho x O y (0.05?x?0.10), polycrystalline samples prepared by the so-called solid state reaction method. Magnetic measurements, M-H and M-T, done by using a PPMS magnetometer, show a paramagnetic behavior including indirect antiferromagnetic coupling between some Ho3+ magnetic moments. In other words, the negative values of the Curie-Weiss temperatures, ?, for the polycrystalline samples with six different Ho concentrations indicate that there is an effective antiferromagnetic coupling among the magnetic moments of Ho3+ ions. However, the decrease in the magnitude of ? with increasing x indicates that this coupling decreases with increasing amount of Ho in the compounds. Furthermore, the effective magnetic moments, µ eff, per Ho atom calculated from the 1/?-T curves gradually increase with increasing concentration. Therefore, the trends of the magnitudes of ?, and µ eff values clearly indicate that apart from the antiferromagnetic coupling there is also an increasing contribution of a ferromagnetic coupling with increasing x. Hence, one may also conclude that the compounds studied seem to have a kind of spin-glass behavior. © 2013 Springer Science+Business Media New York.Acknowledgements This work was supported by Cukurova University (Adana/Turkey) under the project number of AMYO2011BAP3

AC-magnetic susceptibility of Dy doped ZnO compounds

Dy doped ZnO polycrystalline diluted magnetic semiconductor compounds have been prepared by the so called solid state reaction method. We have studied the M-H and AC magnetic properties of the compounds by using a PPMS magnetometer, and explored the phases and crystal structure by using a X-ray powder diffractometer. The XRD spectra of the compounds show that the substitution of Dy3+ for Zn2+ causes almost no change in the hexagonal wurtzite structure of ZnO, and the Dy3+ ions are successfully substituted into the Zn2+ site of the ZnO matrix. The magnetic measurements, M-H and ?-T, for T in the range from 10 to 300 K, show a paramagnetic behavior, including indirect antiferromagnetic couplings between some Dy3+ magnetic moments. Since the Curie-Weiss temperatures, ?, are all negative but decrease in magnitude with increasing Dy concentration. On the other hand, the calculated effective magnetic moments, µeff, per Dy3+ ion slowly increase with increasing Dy concentration, but are all very close to the free ion value of µeff, ~11.0 µB. Therefore, the trends of the magnitudes of ?s and µeff s indicate that the samples are not only paramagnetic but also have antiferromagnetic couplings due to the complex nature of the compounds. In addition, the thermal variation of average magnetic moment, Peff(T), per Dy3+ ion have been calculated, and have been found to be gradually increasing with increasing temperature and Dy concentration. © 2015 Elsevier B.V.All rights reserved.FEF2010YL53The authors are very much thankful to Professor Tezer Fırat of the Physics Department, Hacettepe University for his help during the magnetic measurements. This work was supported by Cukurova University (Adana/Turkey) under the project number of AMYO2011BAP3 and FEF2010YL53

Structural characterization and superconductivity in Bi 1.7Pb0.3-xTbxSr2Ca 3Cu4Oy. The influence of Tb-doping

Bi1.7Pb0.3-xTbxSr2Ca 3Cu4Oy compounds (0.0?×?0.1) are synthesized by using the conventional high temperature melt quenching technique to study the influence of Tb substitution on their high-Tc superconducting properties. The effects of different Tb doping levels on the superconductor structure have been investigated by electrical resistance, magnetoresistance, scanning electron micrographs, and XRD measurements. It has been observed that, with increasing Tb3+ substitution for Pb 2+ the high-Tc Bi-(2223) phase gradually transforms into the low-Tc Bi-(2212) and Bi-(2201) phases. It should be pointed out that the low-Tc superconducting phases of Bi-(2212) and Bi-(2201) are formed for all the doping levels. The data suggest that with the increasing Tb3+ doping level the superconductivity in Bi1.7Pb 0.3-xTbxSr2Ca3Cu4O y system is suppressed due to the destruction of the phase coherence by pair-breaking effects, such as magnetic. The magneto-resistance results clearly demonstrate that with increasing magnetic field first the high-T c Bi-(2223) phase gradually diminishes and almost the low-T c Bi-(2212) phase remains, however, the trends indicate that at a reasonably high magnetic field the low-Tc phase will also be destroyed and hence the superconductivity will not be observed any more, as expected

Physical properties of melt-cast annealed Bi1.6Pb0.4Sr2Ca3Cu4O 12 compound

A Bi1.6Pb0.4Sr2Ca3Cu4O 12 compound was produced by melt-casting method The microstructure of the sample was studied by Scanning Electron Microscopy. Phase analysis was carried out by X-ray diffraction patterns and EDAX. The electrical resistance exhibites the existance of a superconducting phase with an onset temperature Tc at 110 K along with a minor phase with an onset Tc at 80 K. It has been found that the superconducting phase temperature Tc increases with increasing sintering temperature

The effect of Gd concentration on the physical and magnetic properties of Bi1.7Pb0.3-xGdxSr2Ca 3Cu4O12+y superconductors

Bi-Pb-Gd-Sr-Ca-Cu-O bulk samples with nominal composition Bi 1.7Pb0.3-xGdxSr2Ca 3Cu4O12+y (x=0.01, 0.05, 0.075, 0.10) were prepared by the melt-quenching method. The effects of different Gd doping on the structure have been investigated by electrical resistance, scanning electron micrographs, XRD, magnetization and magnetic hysteresis loop measurements. The magnetization measurements have been carried out as a function of magnetic field for fields up to 5 kOe at temperatures well below the zero resistance temperatures of the annealed samples. It has been found that the high-Tc superconducting phase, (2 2 2 3), is formed in the sample A with concentration x= 0.01, annealed at 840°C for 120 h. However, with increasing Gd3+ doping for Pb2+ the (2 2 2 3) phase gradually transforms into the (2 2 1 2) phase. The magnitudes of magnetization and initial susceptibility, M and dM/dH , and the hysteresis loop areas decrease with increasing Gd concentration x and/or temperature T. The fast decreases in M , dM/dH , and the hysteresis loop areas related to the superconducting volume, with increasing x and/or T seem to imply an existence of flux pinning centres in our samples. In order to support this implication the critical current densities Jc, of the samples, have been estimated at two fixed temperatures, 9 and 30 K. Our data have indicated that Jc decreases with increasing temperature and/or Gd concentration, as expected. © 2005 Springer Science+Business Media, Inc.This work is supported by the Research Fund of Çukurova University, Adana, Turkey, under Grant Contracts Nos. AAP-2002-9, no. FBE.2002.D43, no. FBE 2002. D175. The authors wish to thank TAEA (Ankara Nuclear Research and Training Center) for recording the XRD patterns and resistivity measurements

Effects of annealing time on the magnetic properties of a Bi 1.7Pb0.29Gd0.01Sr2Ca 3Cu4O12+y superconductor prepared by the melt-quenching method

Bi-Pb-Gd-Sr-Ca-Cu-O bulk samples with nominal composition Bi 1.7Pb0.29Gd0.01Sr2Ca 3Cu4O12+y (2234) were prepared by the melt-quenching method. The effects of different annealing times on the structure have been investigated by electrical resistance, scanning electron micrographs, and magnetization measurements. The magnetization measurements have been carried out as a function of the magnetic field up to 5 kOe for field temperatures below the zero resistance temperatures of the annealed samples. It has been found that the high-Tc superconducting phase, (2223), can be formed by annealing at 840°C for 120 h. The decrease in magnitude of the initial susceptibility dM/dH and the fast decrease of hysteresis loops, related to the superconducting volume with increasing temperature, seem to imply an existence of flux pinning centers in our samples. © 2005 the Physical Society of the Republic of China