Evidence of discrete energy states and cluster-glass behavior in Sr$_{2-x}$La$_{x}$CoNbO$_{6}$

Ajay Kumar, B. Schwarz, H. Ehrenberg, R. S. Dhaka
We report the detailed analysis of specific heat [C P (T)] and ac susceptibility for magnetically frustrated Sr 2−x La x CoNbO 6 (x = 0-1) double perovskites to understand low-temperature complex magnetic interactions and their evolution with x. Interestingly, the observed Schottky anomaly in the x 0.4 samples shifts gradually toward higher temperatures with magnetic field as well as x, and the analysis reveals the persistence of the discrete energy states in these samples resulting from the
more » ... n-orbit coupling and octahedral distortion. Moreover, the extracted values of the Landé g factor indicate the existence of high-spin state Co 3+ ions energetically close to a nonmagnetic low-spin state. The specific-heat data show the λ-type anomaly for the x 0.6 samples due to evolution of the long-range antiferromagnetic ordering. Our analysis of low-temperature C P (T) data for the x 0.6 samples demonstrates the 3D isotropic Heisenberg antiferromagnetic (AFM) interactions and the temperature-induced second-order AFM-paramagnetic phase transition. More interestingly, we demonstrate the presence of the free Co 2+ -like Kramers doublet ground state in the x = 1 sample. Further, the ac susceptibility and time evolution of the magnetization data reveal the low-temperature cluster-glass-like behavior in the x = 0-0.4 samples, where spin-spin correlation strength decreases with x.
doi:10.5445/ir/1000126925 fatcat:pdfoc2zdgjgztkipg5v3xnpr3e