Fig. 4.

Electronic spin relaxation. Frequency dependence of the out-of-phase component of the ac magnetic susceptibility at zero applied dc field for 1Dy (a), and 2Dy (b) in the mK temperature range (right-hand ordinate) and at standard liquid helium temperatures (left-hand ordinate). The solid lines are best fits to Cole–Cole functions. The electronic spin-lattice relaxation (SLR) rates T₁⁻¹ for 1Dy and 2Dy (c) extracted from Cole–Cole fitting of the data in  a and  b. The solid lines are best fits to Eq. (2), and the denoted temperatures correspond to the estimated Néel temperatures