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

Abstract

Spin glass behavior of phase-separated (PS) manganite La0.22Pr0.40Ca0.38MnO3 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 $T_{\mathrm {CO}} \sim 230$ K, $T_{N} \sim ~175$ K, and $T_{C} \sim 130$ K, respectively. Spin freezing appears at $T 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 ( $T_{f} \approx 104$ K) in the Vogel–Fulcher framework yields a relaxation time $\tau \approx 2.5 \times 10 ^{-9}$ s, activation energy $E_{a} \approx 25$ meV and VF parameter $T_{0} \sim 87$ 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.