Size-dependent ferromagnetic phase transition in Sm0.5Sr0.5MnO3 nanoparticles

Magnetic properties of Sm0.5Sr0.5MnO3 nanoparticles with different particle sizes are investigated. It is found that all the nanoparticles show a first-order ferromagnetic transition under low magnetic fields, but a second-order one above a critical field H-CR. As the particle size decreases, the ferromagnetic transition temperature, the thermal hysteresis width in the magnetizations, and H-CR exhibit a significant decrease, which indicates that the ferromagnetism is weakened and the first-order transition is softened. A detailed analysis on the magnetic susceptibilities of these nanoparticles reveals that this weakening and softening are attributed to the weakened double-exchange interactions and the strongly suppressed charge-ordered antiferromagnetic state by the size reduction, respectively. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3691216]