Effects of Cr doping on the structure, charge ordering, transport and spin ordering state in Nd 0.5Sr 0.5Mn 1− xCr xO 3

Abstract

The effects of cation substitution in the manganese site of charge-ordered Nd 0.5Sr 0.5MnO 3 have been investigated to elucidate how the properties of this material change with chromium doping. Nd 0.5Sr 0.5Mn 1− x Cr x O 3 ( x=0, 0.05, 0.1, 0.15, 0.2, 0.25) compounds have been studied by X-ray diffraction and transport and magnetic measurements. All samples were determined to be single phase and crystallized in an orthorhombic structure. Magnetic measurements showed that chromium doping decreases the charge-ordering temperature T co as x values are increased from 0 to 0.05. The charge ordering is completely destroyed for all the higher Cr doping levels ( x>0.05), and the material changes from an antiferromagnetic insulator to the ferromagnetic metallic (FMM) state for 0.05< x<0.2. The resistivity decreases as the result of a metal–insulator transition for x<0.2, but the resistivity increases, and the material becomes an insulator if x>0.2. At the same time, the magnetization increases with increasing Cr content, reaches a maximum for x=0.15 and then decreases for x>0.15. It is proposed that Cr destroys the charge ordering and facilitates double exchange between Mn 3+–O–Mn 4+. It is thus responsible for the FMM state seen at low Cr doping levels, while an antiferromagnetic interaction between Mn 4+–O–Cr 3+ or Cr 3+–O–Cr 3+ is responsible for the insulator state at high Cr doping levels.