The Structural and Magnetic Properties of Zn0.8-4xDyxOy (0.05 <= x <= 0.10) Compounds Prepared by Solid-State Reactions

WOS: 000323923800015In this study, Dy-doped ZnO (Zn0.8-4xDyxOy (0.05 <= x <= 0.10)) samples were prepared by the solid-state reaction method, and were characterized by using the XRD, SEM and EDX techniques. The SEM results clearly demonstrate that the grains of the samples are very well connected to each other and tightly packed. From the XRD and EDX spectra, it has been concluded that the substituting of Dy3+ for Zn2+ in ZnO causes almost no change in the hexagonal wurtzite structure of ZnO. However, the lattice parameters a and c of Dy-doped ZnO are slightly different from those of the pure ZnO. These observations may be due to the slightly different ionic sizes of Zn2+ and Dy3+ ions. Our magnetization measurements (M-H) and (M-T) show paramagnetic behavior with a negative value of the Curie-Weiss temperature, corresponding to an antiferromagnetic exchange coupling in Dy-doped ZnO. Since, for low magnetic fields the extrapolation of the H/M versus temperature curves cut the T axes at negative values, we believe that the substitution of Dy in ZnO causes an overwhelming antiferromagnetic interaction for x <= 0.10.Cukurova UniversityCukurova University [FEF2010YL53, AMYO2011BAP3]This work was supported by Cukurova University under FEF2010YL53 and AMYO2011BAP3 project numbers

Exploration of the superconducting properties of Y3Ba5Cu8O18 with and without Ca doping by magnetic measurements

WOS: 000297446000009The superconducting Y3Ba5Cu8O18 (Y-358) and Y3Ba5Ca2Cu8O18 (YCa-358) compounds have been synthesized by using the sol gel method. Hence, the influence of doping of Ca into the compound Y-358 has been studied by comparing the resistivities, DC magnetizations both M(H) and M(T),flux pinning properties, AC susceptibilities and critical current densities of the undoped and doped compounds, at low temperatures. The AC susceptibility and resistivity measurements showed that the superconducting transition temperature, T-c, is suppressed (about 6 K) with the addition of Ca into the main compound. The hysteresis loops of YCa-358 show peak like projecting parts at temperatures below 45 K and around zero applied field that may be due to the local modulation of the composition in YCa-358. Such a behavior has been observed for the first time. The critical current densities, J(c), determined from the hysteresis measurements decrease with the addition of Ca into Y-358. At 15 K, the maximum values of J(c), for the compounds Y-358 and YCa-358 are found to be 8 x 10(4) A/cm(2) and 4.5 x 10(4) A/cm(2), respectively. The flux pinning force, F-p. calculated from the field dependence of the J(c) values shows that the irreversibility line shifts to lower magnetic fields with the doping of Ca into Y-358. Furthermore, the measurements of the inphase and out off components of the ACsusceptibilities clearly demonstrate that the superconducting volume fraction of Y-358 decreases with the addition of Ca. (C) 2011 Elsevier Masson SAS. All rights reserved.Cukurova UniversityCukurova University [FEF2009BAP10, AMY02009BAP1, FEF2009YL30]This work was supported by Cukurova University under FEF2009BAP10, AMY02009BAP1, and FEF2009YL30 project numbers. We wish to thank to Mr. Aydin Eraydin for graphical design

Magnetic Properties of Zn1-xNixO (0.25a parts per thousand currency signxa parts per thousand currency sign 0.50) Prepared by Solid-State Reactions

WOS: 000300786300042In this study the origin of ferromagnetism in ZnO-based bulk systems has been investigated using Ni-doped ZnO samples, Zn1-x Ni (x) O with 0.25a parts per thousand currency signxa parts per thousand currency sign0.50, prepared by solid-state reactions. The structural characterizations indicated that the Ni2+ ions almost uniformly distributed in all the samples, and the samples have hexagonal wurtzite structure; however, when x is increased toward 0.50, a new NiO phase is formed. A ferromagnetism (FM) has been observed for all the samples at and below the room temperature. In other words, the room temperature results of (M-H) curves show that the FM observed is intrinsic for all the Ni-doped ZnO samples. However, the saturated magnetizations decrease gradually with increasing Ni concentration. This indicates that, in addition to FM, the excessive doping of Ni in ZnO also causes an antiferromagnetic (AFM) contribution which increases with increasing Ni amount. This result is also supported by the magnetization against temperature measurements. Furthermore, the trend of the ac-susceptibility (chi) versus temperature curves, measured under an ac-magnetic field of 100 Oe, also support our conclusion about the antiferromagnetic contribution to ferromagnetism in our samples.Cukurova University, Adana, TurkeyCukurova University [FEF2009BAP10, AMYO2009BAP1, FEF2005D16]The research work was supported by the Research Fund of Cukurova University, Adana, Turkey, research project no. FEF2009BAP10, no. AMYO2009BAP1, no. FEF2005D16. We wish to thank Aydin Eraydin for his help

The Structural, Superconducting and Transport Properties of the Compounds Y3Ba5Cu8O18 and Y3Ba5Ca2Cu8O18

WOS: 000295609500009This work is related to the structural, superconducting, and transport properties of the compounds Y3Ba5Cu8O18 and Y3Ba5Ca2Cu8O18 prepared by the sol-gel method. The influence of the doping of Ca atoms into the compound Y3Ba5Cu8O18 was studied by employing XRD, SEM, AFM, EDX, DTA, TGA, and the electrical resistivity (rho), Hall coefficient (R (H)), Hall mobility (mu (H)), and magnetoresistance measurements. The XRD spectra showed that Y3Ba5Ca2Cu8O18 almost has the same crystal structure as that of Y3Ba5Cu8O18, except with some impurity peaks. The resistivity measurements have pointed out that the compounds Y3Ba5Cu8O18 and Y3Ba5Ca2Cu8O18 have their T (c)-onset temperatures at approximately 92.7 and 86.6 K, respectively. The Hall coefficients R (H) and Hall mobilities mu (H) have been measured at the 10-300 K temperature interval in a magnetic field of 0.55 T. The signs of R (H) and mu (H) are found to be positive for both samples, which indicate that the conduction is p-type in our samples. As expected, the magnetoresistance results clearly demonstrate a considerable decrease of the offset temperatures with increasing magnetic field.Cukurova University, Adana, TurkeyCukurova University [FEF2009BAP10, AMYO2009BAP1, FEF2009YL30]This work is supported by the Research Fund of Cukurova University, Adana, Turkey, under grant contracts no. FEF2009BAP10, no. AMYO2009BAP1, no. FEF2009YL30. Dr. Osman Serindag, Cukurova University, is gratefully acknowledged for the thermal measurements of the present samples. We wish to thank Aydin Eraydin for his help