Electron Spin Resonance Spectra of ${\hbox {La}}_{0.7}{\hbox {Cd}}_{0.3}({\hbox {Mn}},{\hbox {Co}}){\hbox {O}}_{3}$ Perovskites

We have prepared two perovskite samples La_0.7Cd_0.3MnO₃ (LCMO) and La_0.7Cd_0.3CoO₃ (LCCO) by using a solid-state reaction technique and studied their electron spin resonance (ESR) spectra versus temperature up to ~500 K. Experimental results reveal that as compared to LCMO, the resonant signals of LCCO are weaker and easily extinguished by thermal energy. For both samples, there exists a temperature called T_min at which the narrowest ESR linewidth (ΔH) is obtained. At temperatures , the resonant lines associated with the ferromagnetic phase are asymmetrical. They become a symmetrical single line in the Lorentzian shape when the samples enter the paramagnetic region with T > T_min. A detailed analysis of resonant spectra in this paramagnetic region reveals that temperature dependences of ΔH can be described by a linear function of the single-phonon process. The resonant intensity versus temperature obeys an exponent function I = I₀ exp(E_a/k_BT), where E_a is the activation energy associated with decomposition of ferromagnetic clusters. Temperature dependences of the resonant position (H_r) and the Lande factor (g) indicate the dominance of spin-spin and spin-lattice interactions in both LCMO and LCCO, but with the additional presence of the spin-orbit interaction in LCCO at high temperatures (T > 380 K). We believe that the differences in the electronic structure of e_g and t_g levels, as well as in the electronic spin configuration of Mn and Co ions, caused the distinct difference in the ESR spectra of LCMO and LCCO.