Magnetic properties of superconducting yttrium barium copper oxide (YBa 2 Cu 3 O 7-δ) nanoparticles (27 nm), prepared by a citrate gel modification of the sol-gel technique, have been studied. A ccording to x-ray powder diffraction analysis the nanoparticles have orthorhombic structure. Room temperature magnetizations measured using a vibrating sample magnetometer (VSM) showed that they have 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. So the sample is annealed twice at T= 700 ˚C for 5 h under 0.8 – 0.9 bar of air. This sample showed ferromagnetic hysteresis loop at 300 ˚K.

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