Inhomogeneous Ferromagnetism and Spin-Glass-Like Behavior in $({\rm Nd}_{1-x}{\rm Y}_{x})_{0.7}{\rm Sr}_{0.3}{\rm MnO}_{3}$ With $x=0.21{-}0.35$

The magnetic properties of polycrystalline ceramic samples (Nd
_1-x
Y
_x
)
_0.7
Sr
_0.3
MnO
₃
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/τ
₀
∝ (T
_f
/T
_g
- 1)-zv, where τ
₀
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 τ
₀
= 10
^-21
-10
^-15
s. These values are different from those expected for canonical SG systems with zv = 10 and τ
₀
= 10
^-13
s, revealing the cluster-SG behavior of (Nd
_1-x
Y
_x
)
_0.7
Sr
_0.3
MnO
₃
samples. Notably, the increase in Y content leads to the shift of τ
₀
and zv values toward those of canonical SG systems, which is ascribed to an expansion of SG clusters.