Critical Current Density Obtained from Particle Size Dependence of Magnetization in Y1Ba2Cu3O7-δ Powders
Y1Ba2Cu3O7-δ pellets and wires show a rather small critical current density Jc, determined by the four-probe method, compared with a single crystal. In order to develop wires that have a higher Jc, it is important to determine the reason why Jc degrades to such a small value. The authors estimated Jc from the particle size dependence of magnetization at 4.2 K and 77 K for Y1Ba2Cu3O7-δ powders calcined in air.
A number of Y1Ba2Cu3O7-δ powders, with average particle diameters ranging from 3 to 53 μm, were prepared. These powders were sorted by a classifier. Jc values were derived from linear relationship between magnetization and powder size by using the Bean model. Three major results were obtained from these measurements. The first is that the magnetization is in linear proportion to the particle size in the 1–20 μm range and that it saturates above 20 μm. SEM and TEM observations suggest that individual powders, being smaller than 20 μm, seem to a single-crystal. However, each powder larger than 20 μm in size is made from several grains. This result suggests that grain boundaries limit current flow in the Y1Ba2Cu3O7-δ powder. The second result is that Jc in the Y1Ba2Cu3O7-δ powder, whose particle diameter is less than 20 μm, is 2x106 A/cm2 for 0.3 T at 4.2 K, and 7x104 A/cm2 for 0.03 T at 77 K. The third result is that the temperature dependence of a magnetization is composed by two curves with different Tc values each other. London penetration depths at 0 K, λ0, obtained from initial magnetization at 4.2 K were different from the value obtained at 77 K. This result can be explained by the two phase model.
KeywordsMagnetization Curve Average Particle Diameter Powder Size Initial Magnetization London Penetration Depth
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