Investigating the Effect of Calcination Temperature on Ferromagnetic Properties in Ultra-fine Particles of HoBaCu3O7- High Temperature Superconductors

In this paper، samples were prepared by citrate-gel method at different calcination temperatures in order to investigate the effect of calcination temperature on ferromagnetism behavior in very small particles (submicron particles) of high Tc superconductor HoBa2Cu3O7-δ. In this method، high-purity nitrate salts of Ho، Ba and Cu were used as the starting materials and citric acid as the complex agent. Determination of phase and studying the structural properties of the samples with X-ray powder diffraction (XRD) confirmed the formation of orthorhombic structure for these small particles and bulk samples. The morphology of the samples was investigated by scanning electron microscope (SEM). The superconducting transition temperature of the samples، determined by AC susceptibility measurements، was 93K for the Bulk sample، and it was lower for submicron particles because of oxygen depletion during the citrate pyrolysis reaction in the preparation process. Room temperature magnetizations measured using a vibrating sample magnetometer (VSM) showed that these particles exhibit ferromagnetism behavior at room temperature while the bulk sample، which was prepared by heating the precursor at high temperature، shows a linear magnetization curve، a typical behavior of bulk 123 superconductors.