Stability of charge and orbital order in half-doped Y0.5Ca0.5MnO3 nanocrystallites

In this paper, we report a detailed study of the structure, magnetic, and electrical transport properties in nanocrystallites of hole-doped manganite Y0.5Ca0.5MnO3, with the aim to study the effect of size reduction on the stability of the charge-orbital order and the antiferromagnetic spin order that are seen in the bulk samples of the half-doped manganite. The investigations have been done in the general context of investigating how size reduction affects competing interactions in complex oxides and thus, changes their ground state. The bulk sample of the material (average crystallite size ∼1 μm), with the smallest radius of the cation in A-site (Y), shows a robust charge and orbital ordered insulating state below the transition temperature near 290 K and an antiferromagnetic spin order at 110 K. The experiments carried out on well-characterized nanocrystalline samples, with average crystallite sizes down to 75 nm, establish that the size reduction changes the structural parameters, and the charge and orbital ordering are suppressed. However, the antiferromagnetic spin order (as revealed by neutron diffraction experiments carried out down to 2 K) persists in the nanocrystallites and co-exists with ferromagnetic order below 110 K. The nanocrystalline samples have significant lower resistivities (by few orders) compared to those of the bulk samples in the temperature range 10–300 K. This corroborates the formation of the ferromagnetic moments in the nanocrystallites.