Suppression of Ferromagnetic Properties for La_1-xSr_xMnO₃ (x=0.15) Nanoparticles

Abstract

Magnetic properties of La_1-xSr_xMnO₃ nanoparticles (φ≈2∼3 nm) of x=0 and 0.15 embedded in amorphous SiO₂ were examined. Both the antiferromagnetic (x=0) and ferromagnetic (x=0.15) samples exhibited superparamagnetism with the blocking temperature of ≈40 K. In the temperature dependence of dc susceptibility, the x=0 sample showed a hump at ≈40 K overlapping with a paramagnetic divergence. Aside from the blocking at ≈40 K, the x=0.15 sample demonstrated ferromagnetic characteristics below ≈250 K. The field dependence of magnetization of the x=0 sample is consistent with the prediction of a system consisting of randomly oriented and noninteracting antiferromagnetic fine particles (φ≈2.5 nm). Ferromagnetic moments of the x=0.15 sample was largely suppressed from that expected for the system of independent ferromagnetic fine particles (φ≈2.5 nm).