The effects of Ti doping on the Mn site in the colossal magnetoresistant (CMR) material of ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3$ has been studied by preparing the series ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{Mn}}_{1-y}{\mathrm{Ti}}_y{\mathrm{O}}_3$ $(y=0,$ 0.01, 0.03, 0.05, 0.07, 0.1, 0.2, 0.3). The ${\mathrm{Ti}}^{4+}$ doping separates the system into ferromagnetic (FM) clusters, and the spin coupling between these FM clusters is weakened with increasing doping content. These variations lead to the decrease of the magnetization M and widening of the paramagnetic-ferromagnetic (PM-FM) transition. When $y>~0.1,$ the size of the FM clusters is so small that there is nearly no interaction between these clusters. The PM-FM transition transforms to paramagnetic–spin-glass transition gradually because the cluster spin arranges randomly. Because the substitution of ${\mathrm{Ti}}^{4+}$ depletes the oxygen p holes and leads to the increase of the bipolaron binding energy, the collapse of the unbound polaron density is reduced. Therefore, the resistivity ρ increases, and the temperature $T_{\rho }$ corresponding to the resistivity maximum ${\rho }_{\max }$ shifts to a low temperature with the doping content. For heavy doping, the samples exhibit an insulating behavior in the entire temperature range studied. Moreover, the substitution of the ${\mathrm{Ti}}^{4+}$ ions extremely enhances the CMR effect in the perovskite manganite materials.

• Received 4 January 2000

DOI:https://doi.org/10.1103/PhysRevB.62.15112