Disorder-induced short-range ferromagnetism and cluster spin-glass state in sol-gel derived La0.7 Ca0.3 Mn1-x Cdx O3 (0≤x≤0.2)

Low temperature magnetic and transport properties of the sol-gel derived Cd doped La0.7 Ca0.3 Mn1-x Cdx O3 (0≤x≤0.20) manganite system show ferromagnetism and cluster spin-glass behavior. Metal-insulator transition (MIT) is exhibited only by the samples with x≤0.1; and for higher concentrations (x=0.15 and 0.20), samples are semiconductors. The MIT shifts to the lower temperature regime with increasing Cd content, indicating an increase of disorder in the system. Structural analysis shows local strain-induced small lattice distortion of the Mn O6 octahedra with Cd doping. With increasing Cd content, the system undergoes interesting paramagnetic to ferromagnetic (with x<0.10) as well as paramagnetic to cluster spin-glass (for x≥0.10) transitions. ac susceptibility (χac) and magnetic relaxation measurements confirm this cluster spin-glass behavior. χac is found to follow the critical slowing down law (τ τ0 = ε-zν). The magnetic hysteresis loops indicate a field-induced irreversible ferromagnetic phase due to the presence of "weak" antiferromagnetic domains in the samples with x≥0.10. This typical behavior is found to be most prominent in the sample with x=0.15. The observed cluster spin-glass state is explained by considering the interactions between the ferromagnetic and antiferromagnetic clusters in these doped systems having disorder and reduced geometrical tolerance factor t, which resulted from the random substitution of Mn with Cd ions.