Giant positive magnetoresistance in heterostructure (La0.7Sr0.3MnO3) coated with YBa2Cu3O7 composites

摘要

(La0.7Sr0.3MnO3)x/(YBa2Cu307)x composites were prepared by mixing La0.7Sr0.3MnO3 powders and the sol-gel-derived YBa2Cu3O7 matrix, followed by high-temperature calcinations. Their structural, magnetic properties and magnetoresistance effect have been investigated systematically. A giant positive magnetoresistance (PMR) at low magnetic field is observed at low temperatures. In the case of (La0.7Sr0.3MnO3)i/(YBa2Cu307)9 composite, the PMR achieves 260% under a magnetic field of 5800 Oe. However, the PMR value sharply decreases with increasing temperature and no magnetoresistance effects are found above metal-insulator transition temperature. The enhancement of spin-dependent scattering at the grain boundaries should be responsible for the observed PMR. In addition, the temperature dependence of resistance under magnetic field could be explained by the competition between dia-magnetism and paramagnetism in YBCO phase. At low temperature, the diamagnetism is predominant over paramagnetism and the interface scattering between LSMO grains is enhanced correspondingly. As a result, the low-temperature resistance increases and large PMR appears.