EXPERIMENTAL-STUDY OF THE DEALMEIDA-THOULESS LINE BY USING TYPICAL ISING SPIN-GLASS FEXMN1-XTIO3 WITH X=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 FexMn1-xTiO3 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 x 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(exo)[1-T(SG)(H)/T(SG)(0)]alpha for small fields. It is found that the exponent alpha is very close to 3/2 predicted by the AT theory. Moreover, it is shown that the coefficient A(exp) obtained for FexMn1-xTiO3 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.