Suppression of Spin Glass Behavior in Phase Separated La0.22Pr0.40Ca0.38MnO3 by Nanostructuring

Spin glass behavior of phase-separated (PS) manganite La
_0.22
Pr
_0.40
Ca
_0.38
MnO
₃
is investigated as a function of crystallite size. Various sizes are obtained by heating the chemically synthesized compound at 700 °C (S7) and 1100 °C (S11) for 12 h. Rietveld refinement confirms the single-phase orthorhombic structure. The HRTEM analysis yield typical crystallite size in the range of ~10- 20 nm for S7 and ~300-500 nm for S11, respectively. At larger crystallite size (S11) charge ordering (CO), antiferromagnetic (AFM), and ferromagnetic (FM) transitions are observed sequentially at T
_CO
~ 230 K, T
_N
~ 175 K, and T
_C
~ 130 K, respectively. Spin freezing appears at T <; T
_P
~ 113 K while a weak reentrant magnetic order is seen at further lower temperatures. At nanoscale (S7) CO and AFM transitions do not remain explicit and T
_C
and T
_P
are lowered to ~107 and ~96 K, respectively. In S11, the frequency dispersion of imaginary part spin freezing temperature (T
_f
≈ 104 K) in the Vogel-Fulcher framework yields a relaxation time τ ≈ 2.5 × 10
^-9
s, activation energy E
_a
≈ 25 meV and VF parameter T
₀
~ 87 K. These results point to the canonical spin-glass behavior. It is interesting to note that the nanostructured sample S7 did not show any frequency dispersion. This confirms the suppression of the spin-glass behavior due to the nanostructuring, which is attributed to the surface/interface enhanced spin disorder.