Effect of Ti dopant on the carrier density collapse in colossal magnetoresistance material La0.7Ca0.3Mn1-yTiyO3

The effects of Ti doping on the Mn site in the colossal magnetoresistant (CMR) material of La0.7C0.3MnO3 has been studied by preparing the series La0.7Ca0.3Mn1-yTiyO3 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1, 0.2, 0.3). The Ti4+ doping separates the system into ferromagnetic (FM) clusters, and the spin coupling between these Fh? 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 greater than or equal to 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 Ti4+ 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 p increases, and the temperature T-p corresponding to the resistivity maximum p,, 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 Ti4+ ions extremely enhances the CMR effect in the perovskite manganite materials.