Mixed phase of spin-glass ordering and antiferromagnetism in an Ising system, ${\mathrm{Fe}}_{\mathrm{x}}$${\mathrm{Mn}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{TiO}}_3$

Neutron scattering demonstrates the coexistence of antiferromagnetic order and spin-glass in the Ising system ${\mathrm{Fe}}_{\mathrm{x}}$ ${\mathrm{Mn}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{TiO}}_3$ for x=0.33, 0.60, and 0.65. The behavior of the diffuse intensity as well as the inverse correlation length κ as functions of Fe ion concentration x strongly suggests that there exists a phase boundary between the coexistence phase and the pure spin-glass phase. Thus the phase below the Almeida-Thouless line in an Ising spin-glass system should be distinguished from the pure spin-glass phase.