  Systematic studies of magnetic properties of LaSr2Mn2O7 as a function of
crystalline grain size provide information on how the crystalline grain size
affects the magnetic and charge ordering in this compound. The half-doped
bi-layered manganite LaSr2Mn2O7 (x=0.5) in its bulk form has CE-type
antiferromagnetic (CE-AFM) charge ordering phase transition. In this work, we
have prepared LaSr2Mn2O7 ceramic samples using Pechini sol-gel method to
produce different grain sizes and the effect of crystalline grain sizes between
150 200 to 1000 nm on magnetic properties results obtained by the SQUID
magnetometer have been investigated. The DC magnetization (DCM) measurements
for all samples indicate that the crystalline grain size has no considerable
effect on TCO. Just the temperature of charge ordering peak becomes sharper,
and susceptibility measurement in the zero field cooling (ZFC) and filed
cooling (FC) increases as the grain sizes becomes systematically smaller. The
results obtained from magnetic hysteresis curves confirm the anti-ferromagnetic
phase formation as a ground state and Arrott plots obtained manifest the
existence of first and second order magnetic phase transition in all samples.
In addition, in sample with a grain size of 150 200 nm, enhancement of the
magnetic properties, which is accompanied with the formation of FM phase on the
surface of grain or particle, is observed.
