Reentrant Spin-Glass Transition and a Mixed Phase in an Ising System Fe_xMn_<1-x>TiO_3

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Neutron scattering demonstrates the clear reentrant spin-glass (SG) transition, forthe first time, in the Ising system Fe.Mn. .Ti0. for .X'=0.33, 0.38, 0.60, and 0.65. Thesamples with x=O.4I, 0.50 and 0.55 exhibit paramagnetic to SG behavior upon lowering the temperature. The results confirm the SG and reentrant SG transitions whichwere suggested from the previous bulk susceptibility measurements by Ito et al. Thereentrant SG phase is shown to be actually a mixed phase where the antiferromagneticlong range order coexists with the SG ordering. The behavior of the diffuse intensityas well as the inverse correlation length tc as a function of an Fe Ton concentration xstrongly suggests that there exists a phase boundary between the mixed phase and thepure SG phase. Thus the phase below the AT line in an Ising SG system should bestrictly distinguished from the pure SG phase. By comparing the data of the x= 0.5Ssample to that of the x=O.57 sample, this phase boundary is parallel to the tempera-ture axis within the accuracy of O.5% of the Fe concentration. The topology of the Is-ing SG phase diagram is briefly discussed by contrast to that of the SherringtonKirkpatrick model.
社団法人日本物理学会の論文
1989-04-15