Size effects and interactions in La0.7Ca0.3MnO3 nanoparticles

La0.7Ca0.3MnO3 (LCMO) nanoparticles with average diameter of 16–73 nm were prepared by reactive milling and thermal processing methods. Interaction and size effects on the magnetic properties of the LCMO nanoparticle samples were investigated. Phenomena related to the interparticle interaction, such as an un-overlapping of the M(Hext,T)/MS vs. Hext/T scaling plots and a Curie–Weiss rather than Curie law behavior of the dc susceptibility at high temperatures were analyzed. The magnetization curves of interacting nanoparticles were well described by using the mean-field approximation. The dependence of the blocking temperature TB on the strength of the interactions, magnetic anisotropy, as well as the thermal dependence of magnetization deviates from the expected Bloch law was also estimated.

Research highlights▶ The magnetic characteristic and analysis have been done for La0.7Ca0.3MnO3 nanoparticles with average particle size from 16 to 73 nm fabricated by reactive milling and thermal processing methods. Magnetic measurements showed the existence of magnetic interaction between particles. A mean field approximation can describe well magnetic behavior of interacting nanoparticle assemblies. The blocking temperature decreases with the increase of interaction strength or particle size, which are suggested to be due to contribution of strong magnetic anisotropy. The reduction of saturation magnetization with surface/volume ratio is mainly due to the formation of a nonmagnetic surface shell around the nanoparticles. The temperature dependence of magnetization based on a thermal distribution of spin waves and fit results to a power law Tɛ showed that ɛ decreases from 1.67 to 1.56 as the particle size increases from 16 to 73 nm.