Coexistence of interacting-ferromagnetic and small-antiferromagnetic clusters in La₀.₅Ba₀.₅CoO₃

Original · EN

We report detailed dc magnetization, linear and non-linear ac susceptibility measurements on the hole doped disordered cobaltite La₀.₅Ba₀.₅CoO₃. Our results show that the magnetically ordered state of the system consists of coexisting non-ferromagnetic phases along with percolating ferromagnetic-clusters. The percolating ferromagnetic-clusters possibly start a magnetic ordering at the Curie temperature of 201.5(5) K. The non-ferromagnetic phases mainly consist of antiferromagnetic-clusters with size smaller than the ferromagnetic-clusters. Below Curie temperature the system exhibits an irreversibility in the field cooled and zero field cooled magnetization and frequency dependence in the peak of ac susceptibility. These dynamical features indicate towards the possible coexistence of spin-glass phase along with ferromagnetic-clusters similar to La₁₋ₓSrₓCoO₃ (x≥0.18), but the absence of field divergence in third harmonic of ac susceptibility and zero field cooled memory clearly rule out any such possibility. We argue that the spin-glass phase in La₁₋ₓSrₓCoO₃ (x≥0.18) is associated with the presence of incommensurate antiferromagnetic ordering in non-ferromagnetic phases which is absent in La₀.₅Ba₀.₅CoO₃. Our analysis show that the observed dynamical features in La₀.₅Ba₀.₅CoO₃ are possibly due to progressive thermal blocking of ferromagnetic-clusters which is further confirmed by the Wohlfarth's model of superparamagnetism. The frequency dependence of the peak of ac susceptibility obeys the Vogel-Fulcher law with τ₀≈10⁻⁹s. This together with the existence of an AT line in H-T space indicates the presence of significant inter-cluster interaction among these ferromagnetic-clusters.