Fragmented ferromagnetic-phase and evolution of Re-entrant cluster-glass behavior in La0.6Sr0.4Co1-xAlxO3 (0 ≤ x ≤ 0.15) compounds

We have observed the fragmentation of ferromagnetic-phase with Al3+ substitution in polycrystalline La0.6Sr0.4Co1-xAlxO3 (0 = x = 0.15) perovskite compounds. The introduction of non-magnetic Al3+ ions at the Co3+ sites results in several segregated ferromagnetic domains that interact and demonstrate cluster-glass-like behavior. The structural information and phase purity is determined with X-ray diffraction and Rietveldrefinement. The compounds crystallize in the R-3c space group with some iso-structural distortions. The soft X-ray absorption spectroscopy (SXAS) of cobalt L-2,L-3-edges revealed the heterogeneous electronic phase with a majority of Co3+ ions. The spin-only contribution of Co3+ and Co4+ to the net-effective magnetic moment confirms the presence of High-spin Co3+ (S = 2) and Low-spin Co4+ (S = 1/2) ionic species. The magnetization parameters (theta(p), Tc, Tb, C, and mu(eff)) observed from the (FC-ZFC) dc-magnetization measurements were suppressed with increasing Al3+ concentration. Inhomogeneous magnetic-phase transition is observed due to segregation in the ferromagnetic phase. Hence, in the parent compound, the intrinsic-ferromagnetism weakens with Al3+ substitution. Therefore, the long-range ferromagnetic-ordering fragments into several interacting FM clusters are isolated by a coexisting non-ferromagnetic (Al3+ rich) sub-lattice. The frequency-dependent magnetic acsusceptibility measurements determine a re-entrant cluster-glass nature which is analyzed with the Mydosh parameter (sic), Critical-Slowing-down of spins, and Vogel-Fulcher-formulation.