Magnetic properties of Sm0.1Ca0.9MnO3 nanoparticles

Abstract

Magnetic properties of compacted Sm0.1Ca0.9MnO3 nanoparticles with average particle size of 25 and 60 nm have been investigated. It was found that the relative volume of the ferromagnetic phase decreases with decreasing particle size. Magnetization curves measured in field cooled and zero field cooled mode separate near the transition temperature TC and remain different even in magnetic field of 15 kOe. AC-susceptibility is strongly frequency dependent below TC, although the temperature of the maximum depends on frequency only slightly. Magnetization hysteresis loops exhibit horizontal and vertical shifts, relatively small in 60 nm and much larger in 25 nm particles, due to size-dependent exchange bias effect. The exchange bias field and the coercive field depend in a non-monotonic way on cooling magnetic field, while the asymmetry of remanence magnetization and magnetic coercivity increase monotonously with the increase of cooling field. Applied pressure enhances Curie temperature TC of nanoparticles with a pressure coefficient dTC/dP ≈ 0.6 K kbar−1, close to that of the bulk, suggesting that magnetic state of the core is similar to the bulk state. The thermoremanance and isothermoremanance curves provide fingerprints of irreversible magnetization originating from the presence of glassy component. We have ascribed the magnetic behavior of the nanoparticles to a core-shell scenario with phase separated core containing ferromagnetic clusters embedded in an antiferromagnetic matrix and partially disordered antiferromagnetic or paramagnetic shell. The suppression of the ferromagnetic phase in the core with decreasing particle size may account for the enhancement of the exchange bias effect seen in smaller particles.