Effects of Al doping upon ac susceptibility of Pr0.5Ca0.5MnO3

Pr0.5Ca0.5Mn1−xAlxO3 (0≤x≤0.07) compounds were prepared by standard solid-state reaction. The ac susceptibility of the samples at low temperatures was investigated. The real component χ′ peak at the freezing temperature Tf is suppressed with increasing the frequency. χ′ shows a linear relation between Tf and the logarithm of the frequency. The normalized slope P=ΔTf/TfΔ log10ω is much lower than for canonical insulating spin glass systems (0.06≤P≤0.08). The intensity of imaginary component χ″ at Tf for the x=0, 0.01, 0.02 samples increases with increasing frequency. The results of χ′ and χ″ suggest that the x=0, 0.01, 0.02 samples have a cluster glass ground state. The intensity of χ″ at Tf for the x=0.05, 0.07 samples decreases with increasing frequency, suggesting a phase separation ground state. The intensity of χ″ at Tf for the x=0.03, 0.04 samples decreases with increasing frequency for ω≤701 Hz and increases with further increase of frequency. This complex behavior is ascribed to the competition between the effects of large and small ferromagnetic clusters in the sample. The ground state of the x=0.03, 0.04 samples is the transition state from cluster glass (for the x=0.02 sample) to phase separation (for the x=0.05 sample). AFM cluster blocking and the spin blocking were observed in the same sample.