Non-equilibrium Behavior of the Magnetization in the Helimagnetic Phases of the Rare Earth Alloys R_1-xY_x (R = Gd, Tb, Dy)

We have performed DC and AC magnetization measurements for the rare-earth magnetic alloy systems Gd_0.62Y_0.38, Tb_0.86Y_0.14, and Dy_0.97Y_0.03. These materials commonly exhibit a proper helical magnetic structure, and a ferromagnetic structure at lower temperatures. In all of these materials, a difference between zero-field-cooled (ZFC) magnetization and field-cooled (FC) magnetization and a hysteresis loop in the M-H curve have been observed in the helimagnetic phases. The non-equilibrium behavior is possibly caused by a common nature, e. g., chiral domain structures. In addition to the above behavior, strong non-linearity of the magnetization and slow spin dynamics have been observed around the Ńeel temperature only in Gd_0.62Y_0.38. The spin-glass like behavior observed in Gd_0.62Y_0.38 could be related to a novel glassy state such as a helical-glass state.