Magnetoelectric coupling and magnetoresistance in oxygen-deficient YBCO ceramics

Polycrystalline YBa2Cu3O6.13 ceramics were prepared by solid state reaction.Temperature dependence of dielectric constant of this oxygen-deficient YBCO sample was measured in the frequency range from 100Hz to 1MHz with a HP4294A precision impedance analyzer.An abnormal dielectric behavior was observed in the vicinity of antiferromagnetic phase transition,which is attributed to the induced ferroelectric transition.In addition,room temperature ferroelectric hysteresis loops of the YBCO ceramics were obtained using a RT 6000 ferroelectric analyzer.The results indicate the existence of ferroelectricity in the sample at room temperature.Temperature dependence of dc resistivity of the sample in zero field and in the presence of a 0.4T magnetic field was measured with standard four lead method.It has been found that applying magnetic field reduces the resistivity of the sample and the magnetoresistance MR of YBCO ceramics reaches a value of 60% below the antiferromagnetic phase transition.A sharp drop in magnetoresistance near the magnetic phase transition suggests a strong magnetoelectric coupling which could potentially have important ramifications in devices such as sensors and information storage.The oxygen deficient YBCO ceramics could be a promising candidate for room temperature multiferrocs.