Spin dynamics of La$_{0.845}$Sr$_{0.155}$Mn$_{1-x}$M$_{x}$O$_{3}$ (M = Mn, Cu, Co) perovskites

Influence of the spin-lattice coupling on the magnetoresistance and magnetocaloric properties of La$_{0.845}$Sr$_{0.155}$Mn$_{1-x}$M$_{x}$O$_{3}$ (M = Cu, Co) perovskites has been investigated by means of electron spin resonance (ESR) spectroscopy. It was observed that asymmetrical ESR signals due to ferromagnetic correlations at temperatures T $<$ T$_{min}$ became Lorentzian at T $>$ T$_{min}$, where T$_{min}$ corresponds to the narrowest ESR linewidth. The temperature dependence of the ESR intensity, I(T), for the samples was well described by an expression of I(T) = I$_{o}$exp(E$_{a}$/k$_{B}$T). In the high temperature region, 1/I(T) obeyed the Curie-Weiss law. The minimum linewidth, $\Delta $H$_{min}$, was determined to be 674, 890 and 750 Oe for La$_{0.845}$Sr$_{0.155}$Mn$_{1}$O$_{3}$, La$_{0.845}$Sr$_{0.155}$Mn$_{0.9}$Cu$_{0.1}$O$_{3}$ and La$_{0.845}$Sr$_{0.155}$Mn$_{0.98}$Co$_{0.02}$O$_{3}$, respectively. This indicated an improvement of the spin-lattice coupling in samples with Cu or Co addition. The strongest spin-lattice coupling resulted in the largest magnetocaloric effect in La$_{0.845}$Sr$_{0.155}$Mn$_{0.9}$Cu$_{0.1}$O$_{3}$. The addition of Cu or Co in La$_{0.845}$Sr$_{0.155}$Mn$_{1}$O$_{3}$ reduced its ferromagnetism and conductivity. The mechanism of the spin-lattice coupling is discussed.