  A simple route to prepare Gd$_{0.7}$Sr$_{0.3}$MnO$_3$ nanoparticles by
ultrasonication of their bulk powder materials is presented in this article.
For comparison, Gd$_{0.7}$Sr$_{0.3}$MnO$_3$ nanoparticles are also prepared by
ball milling. The prepared samples are characterized by X-ray diffraction
(XRD),field emission scanning electron microscope (FESEM), energy dispersive
X-ray (EDX), X-ray photoelectron spectroscope (XPS), and Superconducting
Quantum Interference Device (SQUID) magnetometer. XRD Rietveld analysis is
carried out extensively for the determination of crystallographic parameters
and the amount of crystalline and amorphous phases. FESEM images demonstrate
the formation of nanoparticles with average particle size in the range of
50-100 nm for both ultrasonication and 4 hours (h) of ball milling. The bulk
materials and nanoparticles synthesized by both ultrasonication and 4 h ball
milling exhibit a paramagnetic to spin-glass transition. However, nanoparticles
synthesized by 8 h and 12 h ball milling do not reveal any phase transition,
rather show an upturn of magnetization at low temperature. The degradation of
the magnetic properties in ball milled nanoparticles may be associated with
amorphization of the nanoparticles due to ball milling particularly for milling
time exceeding 8 h. This investigation demonstrates the potential of
ultrasonication as a simple route to prepare high crystalline rare-earth based
manganite nanoparticles with improved control compared to the traditional ball
milling technique.
