Narrow Results

In Ni-doped YBCO systems, Ni ions have been generally thought to enter Cu(2) sites; in fact, the relevant arguments never ceased in the past decade, because various experimental results have not achieved a definite and consistent conclusion. The present paper systemically investigates YBa₂Cu_3-xNi_xO_7-δ(x = 0~0.4) cuprates with X-ray diffraction, positron annihilation technique, and simulated calculations. The results show that Ni ions enter Cu(2) sites at the low-doped concentration, as the concentration increases, a certain proportion of Ni ions begin to enter the Cu(1) sites until the appearance of the impurity phase.

In this research, SrFe${}_{12-x}$Ni${}_x$O${}_{19}$ (x$=$ 0 − 1) hexagonal ferrites were prepared by sol-gel auto-combustion method. Effect of Ni substitution on structural, morphological and magnetic properties of nanoparticles was investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM), respectively. The XRD results confirmed that all samples with x$\le$ 0.5 have single phase M-type strontium ferrite structure, whereas for the SrFe${}_{12-x}$Ni${}_x$O${}_{19}$ samples with x$>$ 0.5, the spinel NiFe₂O₄ phase has also appeared. The lattice parameters and crystallite sizes of the powders were concluded from the XRD data and Williamson–Hall method. Magnetic analyses showed that the coercivity of powders decreased from 5672 Oe to 639 Oe while the saturation magnetization increased from 74 emu/g to 81 emu/g with nickel substitution. The results of this study suggest that the strontium hexaferrites doped with Ni are suitable for applications in high density magnetic recording media as well as microwave devices because of their promising magnetic properties.