Magnetic Memory Effects in a Chiral-Glass Phase of a Superconductive Ceramic YBa2Cu4O8

Abstract

The ceramic YBa2Cu4O8 composed of sub-micron size grains is considered as random Josephson-coupled networks of 0 and π junctions and shows successive phase transitions. The upper transition occurs inside each grain at Tc1 and the lower transition occurs among the grains at Tc2 (< Tc1), where a negative divergence of nonlinear susceptibility is found. This critical phenomenon at Tc2 suggests the onset of the chiral-glass phase predicted by Kawamura and Li. We investigated the magnetic memory phenomena in the temperature dependence of thermoremanent magnetization (TRM). The memory effects are observed in TRM measured on heating after the cooling process with a halt at the temperature Ts below Tc2. The results indicate the existence of a glassy phase such as the chiral-glass one.