Size dependence of charge order and magnetism in Sm0.35Ca0.65MnO3

We report a systematic tracking of consequences of size decrease to nanoscale for charge order (CO) and magnetic properties of electron doped manganite Sm0.35Ca0.65MnO3 by magnetization measurements. The bulk form of this system is charge ordered below 270 K and antiferromagnetic (AFM) below 130 K. The bulk sample and nanoparticles of various sizes (mean diameter ∼ 15, 30, 90 nm) were synthesized by sol-gel technique. Our studies show that the robust CO in the bulk gets weakened by size reduction and the nanoparticles exhibit ferromagnetic (FM) ordering. Magnetization at high temperatures, in the paramagnetic region, reflecting the behaviour of the most part of the samples arising due to FM fluctuations caused by double exchange interaction is found to decrease as the particle size reduces. However, at low temperature the trend of FM magnetization as a function of the size is found to be reversed. This result is understood in terms of the dominance of surface effects where uncompensated bonds and an increase in the charge density at the surface layers lead to weak ferromagnetism which increases with decreasing size.