  Nanoparticles (size 20, 40 and 60 nm) of Pr_0.5Sr_0.5MnO_3 are prepared by
sol-gel technique and their magnetic properties are studied using ferromagnetic
resonance and magnetization measurements. A comparison with the properties of
the bulk material shows that the ferromagnetic transition at 265 K remains
unaffected but the anti-ferromagnetic transition at T_N = 150 K disappears in
the nanoparticles. Further, the temperature dependence of magnetic anisotropy
shows a complex behavior, being higher in the nanoparticles at high
temperatures and lower at lower temperatures in comparison with the bulk.
