Experimental Study of the de Almeida-Thouless Line by Using Typical Ising Spin-Glass Fe_x Mn_<1-x>TiO_3 with x=0.41, 0.50, 0.55 and 0.57

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The de Almeida-Thouless (AT) line for Ising spin-glasses has been studied by using the typical Ising spin-glass Fe_xMn_<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 a 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.
社団法人日本物理学会の論文
1994-08-15