Progressive freezing of finite cluster in locally canted spin Co0.3Zn0.7Fe2O4 spinel ferrite system

Linear and non-linear ac-susceptibility measurements at low temperature resolve the magnetic phase transition in disordered Co0.3Zn0.7Fe2O4 spinel ferrite system. First order imaginary part of ac-susceptibility reveals three transitions from 320 K to 80 K. The second and third order ac-susceptibility indicates that this transition is associated with the emergence of finite spontaneous magnetic clusters. These clusters formed due to the presence of Co2+ ions on octahedral site and the magnetic dilution of tetrahedral site below site percolation threshold in spinel ferrite system. As the temperature is reduced, the system transforms from paramagnetic to spontaneous cluster coexist with ferrimagnetic-like spin state. These clusters freeze at around 100 K due to local spin canting effects. The frequency dependence of the third order ac-susceptibility shows the effect of intra- and inter-cluster spin variation with frequency. This is supported by ac-field amplitude dependence susceptibility results. The above results agree with neutron diffraction studies reported earlier on the same system suggesting the formation of cluster and local canted spin state at low temperature.