Coexistence of considerable inter-particle interactions and spin-glass behavior in La0.7Ca0.3MnO3 nanoparticles

We have studied the magnetic and spin-glass (SG) properties of La0.7Ca0.3MnO3 single-crystalline nanoparticles, which were prepared by the mechanical milling method with different milling times (tm). Analyzing the susceptibility data in the paramagnetic region indicates both ferromagnetic (FM) and anti-FM interactions coexisting in nanoparticles. Additionally, there is a peak associated with the freezing temperature (Tf) appearing on the real part curve of the ac susceptibility, χ′(T). The Tf value increases with increasing frequency as expected for SG systems. The SG behavior was also checked by using the criterion parameter c = ΔTf/TfΔ(log10f), and the power law τ = τ0(T/Tg − 1)−zν. The obtained values of c ≈ 5 × 10−2, τ0 ≈ 10−5 s and zν ≈ 2–3 are consistent with those expected for SG-like systems, suggesting an existence of a SG phase transition at Tg below Tf, which decreases with decreasing 〈D〉. Basing on ln(f) versus Tf data, and the Néel-Arrhenius model [ln(f) = ln(f0) - Ea/kBT] and Vogel–Fulcher law [ln(f) = ln(f0) - Ea/kB(T - T0)], the Larmor frequency (f0), activation energy (Ea) and effective temperature (T0) for the samples with different 〈D〉 were determined. Obtained results indicate the existence a strong interaction between nanoparticles