Magnetic defects in La/sub 2-//sub x/Sr/sub x/CuO/sub 4-//sub delta/

We report the magnetization as a function of magnetic field and temperature for as-grown and doped La/sub 2/CuO/sub 4/. Two samples of La/sub 2/CuO/sub 4/ with differing oxygen treatment and a sample of La/sub 1.995/Sr/sub 0.005/CuO/sub 4/ exhibited T/sub N/ of 225, 240, and 215 K, respectively. An anomalous magnetic field dependence of the magnetization was observed above and below T/sub N/ for each of these samples, suggestive of the presence of small ferromagnetically coupled domains present within each of these samples. Below T/sub N/ these ferromagnetic regions appear antiferromagnetic until application of a critical field switches them to a ferromagnetic domain. Samples of La/sub 2-//sub x/Sr/sub x/CuO/sub 4/ with x = 0.05 and 0.15 show no antiferromagnetic ordering and no anomalous ferromagnetic domains. These anomalous magnetic effects give credence to models of formation of unusual magnetic domains within these antiferromagnetically coupled materials.