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

Studies of magnetic viscosity are presented for the amorphous (Fe0.64Mn0.36)₇₅{P}₁₆B₆{Al}₃$ as a function of temperature ($4.2<~T<~36$ K) and field ($50 Oe<~H<~10 kOe$). The slow changes of magnetization with time are described by $M(t)={M}₁+Slnt$. The coefficient $S$ is found to be field and temperature dependent. For the remanent magnetization, $|S(H)|$ increases with field and then maintains a roughly constant value. For the in-field relaxation, $S(H)$ exhibits a maximum and for each temperature we find a critical field for which $S=0$. The line of critical fields is identified as the de Almeida-Thouless line.