高Tc超导体REBa_2Cu_3O_(7-y)的M-H曲线特性和磁性超导共存

CHARACTERISTIC CURVES OF M-H AND COEXISTENCE OF MAGNETISM WITH SUPERCONDUCTIVITY FOR HIGH Tc SUPERCONDUCTORS REBa_2Cu_3O_(7-y)

合成出零电阻温度90K左右的高Tc超导体REBa_2Cu_3O_(7-y)(RE=Sm、Eu、Gd、Dy、Ho、Er、Tm),磁性稀土离子对转变温度影响不大,但磁性行为各不相同。在77K测量了它们的磁滞回线,在RE=Gd、Dy、Ho、Er、Tm样品中发现超导和磁性共存现象,这预示着有两种可能的共存方式。实验表明,这些超导体的顺磁性强弱规律与稀土离子在其它晶体中的规律相同,说明超导体的磁性来源于稀土离子。某些样品在低温下表现出反铁磁序,有效玻尔磁子数与三价自由稀土离子值一致。

Some high Tc superconductors REBa_2Cu_3O_(7-y) (RE=Sm, Eu, Gd, Dy, Ho, Er, Tm) have been prepared and their critical temperatures Tc are about 90K. The effect of magnetic rare earth ions on the transition temperatures is not very great, but their magnetic behaviours are different one another. The magnetization loops of these compounds have been measured at 77K. The coexistence of superconductivity with magnetic ordering (COSM) occurs in the samples of RE=Gd, Dy, Ho, Er, Tm, predicts that there are two possible ways of coexistence in the samples. These experiments show that the relation of paramagnetism to the atomic number of rare earth elements for these superconductors is similar to that of rare earth ions in some paramagnetic salt crystals, which indicates that the magnetism of the samples originates from the local magnetic moments of rare earth ions. Some Samples were antiferromagnetic ordering at low temperature, and the effective Bohr magneton numbers are consistence with that of free rare earth ions. Some superconductivity parameter and critical current are calculated according to Ginzberg-Landau theory and critical state model.