EFFECTIVENESS OF IRON CLUSTERS AS PINNING CENTERS IN THE YBA2(CU1-XFEX)3OY SYSTEM

The magnetic hysteresis curve of YBa2(Cu1-xFex)3Oy (0 less-than-or-equal-to x less-than-or-equal-to 0.08) prepared by means of two kinds of heat treatment was measured by superconducting quantum interference device (SQUID) magnetometer. YBa2(Cu1-xFex)3Oy samples were slowly cooled from 890-degrees-C in air, and then some were heated at 800-degrees-C in N2 gas. All products, including those heated in N2 gas, were annealed at below 400-degrees-C in O2 gas. The difference DELTA-M in the hysteretic magnetization between the increasing and decreasing magnetic fields of the samples treated in N2 gas shows the maximum value at x = 0.02. This indicates that the clustered Fe atoms formed in the Cu1-O planes act as effective pinning centers for flux lines.