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

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 degrees C (S7) and 1100 degrees C (S11) for 12 h. Rietveld refinement confirms the single-phase orthorhombic structure. The HRTEM analysis yield typical crystallite size in the range of similar to 10-20 nm for S7 and similar to 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 similar to 230 K, T-N similar to 175 K, and T-C similar to 130 K, respectively. Spin freezing appears at T < T-P similar to 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 similar to 107 and similar to 96 K, respectively. In S11, the frequency dispersion of imaginary part spin freezing temperature (T-f approximate to 104 K) in the Vogel-Fulcher framework yields a relaxation time tau approximate to 2.5 x 10(-9) s, activation energy E-a approximate to 25 meV and VF parameter T-0 similar to 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.