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

Studies of magnetic viscosity are presented for the amorphous (Fe0.64Mn0.36)75P16B6Al3 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)=M1+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.