Dopant-dependent impact of Mn-site doping on the critical-state manganites: R0.6Sr0.4MnO3 (R=La, Nd, Sm, and Gd)

摘要

Versatile features of impurity doping effects on perovskite manganites,$R_{0.6}$Sr$_{0.4}$MnO$_{3}$, have been investigated with varying the doingspecies as well as the $R$-dependent one-electron bandwidth. Inferromagnetic-metallic manganites ($R$=La, Nd, and Sm), a few percent of Fesubstitution dramatically decreases the ferromagnetic transition temperature,leading to a spin glass insulating state with short-range charge-orbitalcorrelation. For each $R$ species, the phase diagram as a function of Feconcentration is closely similar to that for $R_{0.6}$Sr$_{0.4}$MnO$_{3}$obtained by decreasing the ionic radius of $R$ site, indicating that Fe dopingin the phase-competing region weakens the ferromagnetic double-exchangeinteraction, relatively to the charge-orbital ordering instability. We havealso found a contrastive impact of Cr (or Ru) doping on a spin-glass insulatingmanganite ($R$=Gd). There, the impurity-induced ferromagnetic magnetization isobserved at low temperatures as a consequence of the collapse of the inherentshort-range charge-orbital ordering, while Fe doping plays only a minor role.The observed opposite nature of impurity doping may be attributed to thedifference in magnitude of the antiferromagnetic interaction between the dopedions.