Particle Size Effects on Charge Ordering and Exchange Bias in Nanosized Sm0.43Ca0.57MnO3

Size dependence of magnetic properties of Sm0.43Ca0.57MnO3 nanoparticles with average size of 15–60 nm has been investigated. Charge ordering, characteristic for the bulk form of this material, was found to be gradually suppressed with decreasing particle size and fully disappearing in 15 nm nanoparticles. Onsets of ferromagnetic contributions to the magnetization appear below 90 K, independently on the particle size, while spontaneous magnetization at 10 K increases with decreasing particle size. Magnetic hysteresis loops exhibit size dependent exchange bias effect manifested by horizontal HEB and vertical MEB shifts, appearing after field cooling. Variation of HEB and MEB shows opposite size dependences; HEB decreases while MEB increases with decreasing particle size. For large 60 nm particles, HEB decreases monotonously with increasing temperature, while for the smallest 15 nm particles it shows surprising nonmonotonic temperature dependence. Size and temperature dependences are discussed in terms of m...