Time Decay of the Remanent Magnetization in Spin-Glasses

The time decay of the thermoremanent magnetization (${\sigma }_{\mathrm{TRM}}$) has been measured in 1.0% Cu: Mn and 2.6% Ag: Mn spin-glasses. It is shown that ${\sigma }_{\mathrm{TRM}}$ is neither an algebraic nor a logarithmic function of time, but it is found that ${\sigma }_{\mathrm{TRM}}$ can be characterized by a "stretched" exponential: ${\sigma }_{\mathrm{TRM}}={\sigma }_0\exp [-\frac{C{\left(\omega t\right)}^{1-n}}{\mathrm{}(1-n)\mathrm{}}]$. Similar time dependences appear in the disorder-diffusion theory of Grassberger and Procaccia and the cooperative-relaxation theory of Ngai, but neither theory in its present form is directly applicable to spin-glasses.