Experimental Study of the de Almeida-Thouless Line by Using Typical Ising Spin-Glass FexMn1-xTiO3withx= 0.41, 0.50, 0.55 and 0.57

The de Almeida-Thouless (AT) line for Ising spin-glasses has been studied by using the typical Ising spin-glass Fe x Mn 1- x TiO 3 with x =0.41, 0.50, 0.55 and 0.57. The spin-glass transition temperatures in fields H between 2.0 Oe and 4.0×10 4 Oe, T SG ( H ), were determined by the dc-magnetization measurements. The field dependence of T SG ( H ) is well described by the equation H = A exp [1- T SG ( H )/ T SG (0)] α for small fields. It is found that the exponent α is very close to 3/2 predicted by the AT theory. Moreover, it is shown that the coefficient A exp obtained for Fe x Mn 1- x TiO 3 is in much better agreement with the value given by the Ising Sherrington-Kirkpatrick model than any other systems, which shows the validity of the AT theory for Ising spin-glasses. This result evidences the existence of the spin-glass transitions in finite fields for Ising systems.