Transition from AFM Spin Canting to Spin Glass-AFM Exchange as Particle Size Decreases in LaFeO3

In this work, we have studied structural and magnetic properties of LaFeO3 as a function of the particle size d, from bulk (d >> 1 mu m) to nanoscale (d approximate to 30 nm). A large number of twins were observed for large particles that disappear for small particle sizes. This could be related to the softening of the FeO6 distortion as particle size decreases. It was observed that the bulk sample showed spin canting that disappeared for d similar to 125 nm and can be associated with the smoothening of the orthorhombic distortion. On the other hand, for d < 60 nm, the surface/volume ratio became high and, despite the high crystallinity of the nanoparticle, a notable exchange effect bias appeared, originated by two magnetic interactions: spin glass and antiferromagnetism. This exchange bias interaction was originated by the formation of a magnetic core-shell: the broken bonds at the surface atoms give place to a spin glass behavior, whereas the inner atoms maintain the antiferromagnetic G-type order. The LaFeO3 bulk material was synthesized by the ceramic method, whereas the LaFeO3 nanoparticles were synthesized by the sol-gel method; the particle size was varied by annealing the samples at different temperatures. The physical properties of the materials have been investigated by XRD, HRTEM, TGA, and AC and DC magnetometry.

Automated summary

In this study, the structural and magnetic properties of LaFeO3 were investigated as a function of particle size ranging from bulk to nanoscale. It was found that the presence of twins decreased as the particle size decreased, which could be attributed to the softening of FeO6 distortion. The spin canting observed in the bulk sample disappeared for smaller particle sizes, possibly due to the reduction in orthorhombic distortion. Additionally, when the particle size was less than 60 nm, a significant exchange effect bias appeared, resulting from the combination of spin glass and antiferromagnetism.