Linear and Nonlinear ac-Susceptibilities of the Spin-Glass and Reentrant-Spin-Glass Mn_xMg_1-xTiO₃

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The temperature variations of linear and nonlinear ac-susceptibilities have been measured for both spin-glass and reentrant-spin-glass samples of the diluted antiferromagnet Mn_xMg_1-xTiO₃. In the temperature variations of the nonlinear susceptibility, a divergence-like peak is observed for the spin-glass samples with x=0.54 and x=0.56 at the respective spin-glass freezing temperatures. A distinct anomaly is also observed for the reentrant-spin-glass sample with x=0.60 at the reentrant transition temperature, indicating a divergent nature of the nonlinear susceptibility. As far as the authors know, it is the first observation for antiferromagnet-base reentrant-spin-glasses. Although the detail of the reentrant transition has not been understood very well yet, this anomaly may suggest experimentally that the reentrant transition should be a genuine cooperative phenomenon of the spin system.