Spin dynamics and magnetic frustration effects in La_(1-x)Sr_xCoO_3 (0 < x≤0.5) compounds

摘要

La_(1-x)Sr_xCoO_3 (0 < x≤0.5) have been thoroughly studied by means of dc magnetization, ac susceptibilities, and electron-spin-resonance (ESR) spectra. Spin-glass behavior and its transition process for x < 0.2 compositions appeared to occur at temperature T_g ranging from 14.6 to 68 K, whereas for further strontium substitution the system was characterized by growing ferromagnetic clusters. The frequency dependence of the spin-glass freezing temperature T_f has been analyzed using the conventional critical slowing-down scaling law. The temperature dependence of T_a with respect to the external magnetic field H_(ex) obeyed an exponential function of θ_a=T_a/T_C∝—H_(ex)~n. A complete magnetic phase diagram of La_(1-x)Sr_xCoO_3 is drawn up. Besides, the internal dynamics in the samples are elucidated by the ESR spectra. The results obtained provide more insights into the nature of spin dynamics and so-called magnetic frustration phenomena in such a cobaltate system.