Effect of disorder on the magnetization of a spin glass

Abstract

The magnetization of spin glasses cooled in zero field show a characteristic logarithmic increase with time. If the sample is held at a measuring temperature just below the transition temperature for a waiting time ${t}_{w}$ the dependence on $\mathrm{ln}t$ is faintly sigmoidal; so, the derivative with respect to $\mathrm{ln}t$ has a maximum, which is at about $\mathrm{ln}{t}_{w}.$ We present results that show that this logarithmic time dependence also occurs in the nondisordered, fully frustrated pyrochlore ${\mathrm{Y}}_{2}{\mathrm{Mo}}_{2}{\mathrm{O}}_{7}.$ However, it differs from that in conventional spin glasses in that the maximum in the derivative is very broad and is not centered on ${t}_{w}.$ The introduction of disorder by replacing some of the Mo with nonmagnetic Ti has the effect of markedly increasing the time-dependent moment, and restores the usual spin-glass behavior.