Experimental study of the temperature-field phase diagram of spin-glasses

Studies of magnetic viscosity are presented for the amorphous ${\left({\mathrm{Fe}}_{0.64}{\mathrm{Mn}}_{0.36}\right)}_{75}$ ${\mathrm{P}}_{16}$ ${\mathrm{B}}_6$ ${\mathrm{Al}}_3$ as a function of temperature ($4.2<~T<~36$ K) and field ($50 \mathrm{Oe}<~H<~10 \mathrm{kOe}$). The slow changes of magnetization with time are described by $M\left(t\right)=M_1+S\ln t$. The coefficient $S$ is found to be field and temperature dependent. For the remanent magnetization, $\mathrm{}\left|S\right(H\left)\right|$ increases with field and then maintains a roughly constant value. For the in-field relaxation, $S\left(H\right)\mathrm{}$ exhibits a maximum and for each temperature we find a critical field for which $S=0\mathrm{}$. The line of critical fields is identified as the de Almeida-Thouless line.