Magnetic properties of superconducting YBa2Cu3O7-δ nanoparticles have been studied. They have prepared by the citrate gel modification of the sol-gel technique [1]-[2]. Different particle sizes were obtained by calcination of Precursor powder in oxygen atmosphere at 860 (A1 sample) and 900˚ C (B1 sample) [3]. After light grinding, the samples were annealed at 700 ˚C for 2 h in flowing O2 (A2, B2). Room temperature magnetizations measured using a vibrating sample magnetometer (VSM) showed that they have weak magnetic properties. The development of ferromagnetism is attributed to the presence of surface oxygen vacancies that lead to electron redistribution on the different ions at the surface. For development of magnetization, the samples were annealed at 700 ˚C for 5 h under 0.8 - 0.9 bar of air (A3 ≈ 33, B3 ≈ 46 nm). A ccording to x-ray powder diffraction analysis the nanoparticles have orthorhombic structure (Figure 1). The sizes of crystalline were estimated from the width of the (031) XRD peak using the scherrer formula. The ferromagnetic moment increases with decreasing the particle size. You can see M(H) curves of A2, B2 samples in Figure 2 and A3, B3 in Figure 3 respectively, which clearly indicate that annealing at vacuum improves ferromagnetic properties of the samples

Keywords