No abstract

Versatile features of impurity doping effects on perovskite manganites, R 0:6 Sr 0:4 MnO 3 , have been investigated by varying the doping species as well as the R-dependent one-electron bandwidth in the single-crystalline specimens. In ferromagnetic-metallic (FM) manganites (R ¼ La, Nd, and Sm), a few percent of Fe substitution dramatically decreases the ferromagnetic transition temperature, leading to a spin glass insulating (SGI) phase for each R species. There, the correlation of charge-orbital ordering in competition with metallic ferromagnetism is effectively induced, which has been observed as an evolution of diffuse electron scattering even in the R ¼ La system with the largest bandwidth. Such a marked impact of Fe doping, widely observed in a variety of FM manganites, virtually results in the reduction in the bandwidth for the system in the critical region near the SGI phase. We have also found a contrastive impact of Cr (or Ru) doping on a SGI manganite (R ¼ Gd). For these dopants, the impurityinduced ferromagnetic magnetization is observed at low temperatures as a consequence of the collapse of the inherent short-range charge-orbital ordering, whereas Fe doping gives only a minimal influence. Thus, the opposite nature of Fe and Cr doping tends to generally hold for bicritical-state manganites with various bandwidths and phase correlation lengths. This may stem from the difference in magnitude of the antiferromagnetic interactions between the Fe-Fe and Cr-Cr couplings.