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
_0.7
Cd
_0.3
MnO
₃
(LCMO) and La
_0.7
Cd
_0.3
CoO
₃
(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 = I
₀
exp(E
_a
/k
_B
T), 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.