No abstract

Recently, the so-called room-temperature ferromagnetism in any nanoparticles has been studied intensively. It is well known that the properties of ferromagnetism and superconductivity are contradictory in a superconducting high-Tc cuprate. The existence of ferromagnetism in the nanoparticles has been suggested to occur on the surface. This magnetism has been expected to come from defects inducing magnetic moments on oxygen vacancies at the surface of the nanoparticles. This work is to observe magnetism in nanosized superconducting Pr2-xCexCuO4 (PCCO) with x = 0.15 by means of a superconducting quantum interference device (SQUID). The magnetization curves of the reduced PCCO nanoparticles with the superconducting transition temperature, Tc, of ~25 K have revealed that there is weak ferromagnetism observed at room temperature. The magnitude of magnetization could be enhanced by oxygen reduction annealing in vacuum with increasing annealing temperature. A non-linear magnetization occurring in the reduced PCCO nanoparticles through the vacuum annealing process is probably due to a strong oxygen reduction producing more oxygen vacancies in the T'-structure.

No abstract

The composition of (1-x) (Ba0.85Sr0.15)TiO3 – x (K0.5Na0.5)NbO3 (BST-KNN) for x=0.1 and x=0.2 were successfully prepared by two separate synthesis namely oxalate co-precipitation (for BST) and solid-state reaction (for KNN). Sintered pellet at 1200 °C for 2h exhibits a single phase except x= 0.2 showing a secondary phase and was identified as Ba2TiO4. KNN doped BST system show tetragonal symmetry in which higher dopant expand its tetragonality (c/a). The density of sintered samples deduced by Archimedes method are slightly higher than 90%. Permittivity measurements as function of temperature show almost similar Tc= 90 °C at frequency 1.273 kHz and shift to higher temperature as frequency increases indicating a typical relaxor characteristics. At room temperature the relative permittivity showing Debye relaxation characteristic with ωr=12560 (x=0.1) and ωr =20096 (x-0.2). Furthermore, as function of temperature the activation energy deduced from relaxation time was obtained Ea=0,564 eV for x=0.1 and 0,58 eV for x=0.2.

No abstract