Influence of Ti-doping on the magnetic exchange interaction of La0.5Ca0.5MnO3 nanoparticles
Résumé
The striking effect of Ti-doping on the magnetic properties of La0.5Ca0.5MnO3 nanoparticles have been investigated by different methods. The half doped manganites are at the boundary between the ferromagnetic metallic and antiferromagnetic insulating phases. There is a delicate balance between ferromagnetic double exchange and antiferromagnetic superexchange interactions. In half doped La0.5Ca0.5MnO3 charge ordered antiferromagnetic state is destabilized below a critical size followed by development of ferromagnetism. We have seen that slight disturbance in magnetic exchange interactions by Ti-substitution (>5%) drastically changes the fraction of ferromagnetic clusters. The ferromagnetic Mn3+-O-Mn4+ interaction is suppressed by Mn3+-O-Ti4+ type of interactions. For more than 10% Ti doping the surface ferromagnetic character of the nanoparticles is largely weighed down. This suppression of ferromagnetic component by diamagnetic Ti-doping eventually leads to phase separated states with lower magnetization value.