Inhomogeneous Ferromagnetism and Spin-Glass-Like Behavior in With

The magnetic properties of polycrystalline ceramic samples (Nd_1-xY_x)_0.7Sr_0.3MnO₃ with x = 0.21 - 0.35 were studied by means of dc magnetization and ac susceptibility measurements. Experimental results reveal a strong decrease of the ferromagnetic (FM)-paramagnetic phase-transition temperature (T_C) from 97 to 65 K as increasing x from 0.21 to 0.35, respectively. There is magnetic inhomogeneity associated with short-range FM order. Particularly, the samples undergo a spin-glass (SG) phase transition at the so-called blocking temperature (T_B) below T_C, which shifts toward lower temperatures with increasing the applied field, H_ex; T_B → T_g (the SG phase-transition temperature) as H_ex → 0. The existence of the SG behavior in these samples was also confirmed by frequency (f) dependences of the ac susceptibility. For the in-phase/real component, χ´(T), it shows a frequency-dependent peak at the SG freezing temperature (T_f); T_f → T_g as f → 0. Dynamics of this process were analyzed by means of the slowing down scaling law, τ/τ₀ ∝ (T_f /T_g - 1)-zv, where τ₀ and zv are the characteristic time and critical exponent, respectively. Fitting the experimental T_f (f) data to the scaling law gave the results of zv = 10.1-12.3 and τ₀ = 10^-21-10^-15s. These values are different from those expected for canonical SG systems with zv = 10 and τ₀ = 10^-13s, revealing the cluster-SG behavior of (Nd_1-xY_x)_0.7Sr_0.3MnO₃ samples. Notably, the increase in Y content leads to the shift of τ₀ and zv values toward those of canonical SG systems, which is ascribed to an expansi- n of SG clusters.