MAGNETIC HYSTERESIS IN LA1.85SR0.15CUO4

Detailed measurements of the magnetic properties of the high-temperature superconductor La//1//. //8//5Sr//0//. //1//5CuO//4 as a function of field (20 G less than equivalent to H less than equivalent to 35 kG) and temperature (1. 5 less than T less than 40 K) are reported. The magnetic cycle is characterized by at least three different regimes of magnetic behaviors, associated with three characteristic fields H//c//1*, H* and H//c//2. The initial m vs multiplied by (times) H relationship is linear and reversible up to a threshold value H//c//1* representing an upper limit for the first critical field H//c//1. The effective volume fraction from which flux is screened attains 70% at the lowest temperatures. As H is further increased a regime of strong irreversibilities takes place in fields up to a second threshold field H*(T) beyond which the magnetization curve becomes again reversible. The magnetic loop is in many aspects similar to that of extreme second-kind granular superconductors in which intragrain supercurrents could exceed 10**6 A/cm**2.