Size-induced ferromagnetism and metallicity in Nd0.5Sr0.5MnO3 nanoparticles: A neutron diffraction study

The phenomenon of destabilization of antiferromagnetic insulating state into a ferromagnetic metallic one in Nd_0.5Sr_0.5MnO₃ with the variation of particle/grain size is critically investigated. Based on our neutron diffraction study, magnetic and transport experiments, we observe ferromagnetism and metallic behavior in Nd_0.5Sr_0.5MnO₃ (∼40 nm grain size) as against A-type antiferromagnetic order in the sample with the largest grain size (∼800 nm). The latter shows a systematic change in the lattice parameters with temperature, and an antiferromagnetic ground state similar to that of a bulk system. Interestingly, the sample with the smallest grain sizes exhibits insignificant structural changes (compared to the largest grain size sample) but a complete change in the magnetic state (ferromagnetic behavior) as revealed from the neutron diffraction study. Magnetic measurements also confirm a ferromagnetic state in the small-grained sample. Electronic transport measurements exhibit a metal-insulator transition in this sample. The effects are primarily attributed to enhanced surface disorder.