Magnetotransport properties of the perovskite Nd0.67Sr0.33Mn1-xCoxO3 single crystals

The effect of Co doping on the Mn site in the ferromagnetic phases of the perovskite Nd0.67Sr0.33Mn1-xCoxO3 has been studied in order to determine the relative importance of the double-exchange interaction. The measured single crystals were grown by the floating-zone method. Conduction and ferromagnetism are suppressed by Co doping. The resistivity for x=0.1 material has a large peak near Tc, where a metal-insulator transition seems to take place. Besides, the magnetic field of 7 T causes the colossal magnetoresistance of 96% there, which is a little larger than 94% for mother x=0 material. The materials with x above 0.1 show a spin-glass-like or cluster-glass-like behavior instead of a long-range ferromagnetic order for x=0 and 0.05 materials. The material with x=0.3 shows the typical spin-glass and insulating behaviors with rather small magnetoresistance. These results are ascribed to the frustration of random competing double-exchange ferromagnetic and super-exchange antiferromagnetic interactions with the introduction of Co3+/Co4+ ions. The spin-state transition of Co3+ ions from high to low spin on lowering the temperatures probably plays an important role in preventing the long-range ferromagnetic order and decreasing the pathways for carrier hopping