Relaxation of the magnetization in high-T_c superconductors

Logarithmic time decays of the magnetization M have been observed in SrLaCuO and BaLaCuO specimens. If a small field Hi < HC1 is applied to a virgin specimen, the isothermal dc magnetization M is unstable and decays in time following the law M-M0 α THin1n( t t0) with n {reversed tilde equals} 3 over an observation period of 105 sec. If the field Hi is removed, the same law is followed at H = 0 with a logarithmic rate ∂M ∂lnt about a factor of three smaller. This indicates that these substances have a strong "memory" of the field Hi applied previously. © 1988.