  The magnetic order of La0.7Sr0.3MnO3 nanoparticles (NPs) fabricated in a SPEX
D8000 mill was systematically studied. The La0.7Sr0.3MnO3 nanocrystals grow
from the milled constituent oxides during the milling processes. The
magnetization data obtained by using a SQUID magnetometer show the NPs as a
superparamagnet in terms of anhysteretic curves near room temperature.
Unoverlaping of the scaled M(H-ext, T)/M-s vs. H-ext, T plots and the dc
susceptibility obeying the Curie-Weiss behavior rather than the Curie law at
high temperatures provide evidence that the NPs are interacting
superparamagnetic ensembles. A mean-field correction to the Langevin function L
([H-ext + alpha M]/k(B)T) worked well for the magnetic ordering of the NPs. By
means of the Langevin fitting, the diameter of the NP was estimated to be lower
than 15 nm, depending oil the milling time. The saturation magnetization of NPs
varied from 48.5 em/g to 19 emu/g, with the higher value corresponding to a
larger particle size. A core-shell structure of the NP was adopted, with the NP
having the core-shell magnetically-effective mass density. This is applicable
to the variation of the saturation magnetization with particle size.
