Reentrant Spin-Glass Transition and a Mixed Phase in an Ising System FexMn1-xTiO3

Abstract

Neutron scattering demonstrates the clear reentrant spin-glass (SG) transition, for the first time, in the Ising system Fe x Mn 1- x TiO 3 for x =0.33, 0.38, 0.60, and 0.65. The samples with x =0.41, 0.50 and 0.55 exhibit paramagnetic to SG behavior upon lowering the temperature. The results confirm the SG and reentrant SG transitions which were suggested from the previous bulk susceptibility measurements by Ito et al . The reentrant SG phase is shown to be actually a mixed phase where the antiferromagnetic long range order coexists with the SG ordering. The behavior of the diffuse intensity as well as the inverse correlation length κ as a function of an Fe ion concentration x strongly suggests that there exists a phase boundary between the mixed phase and the pure SG phase. Thus the phase below the AT line in an Ising SG system should be strictly distinguished from the pure SG phase. By comparing the data of the x =0.58 sample to that of the x =0.57 sample, this phase boundary is parallel to the temperature axis within the accuracy of 0.5% of the Fe concentration. The topology of the Ising SG phase diagram is briefly discussed by contrast to that of the Sherrington-Kirkpatrick model.