Temperature dependence of activation energy of the conductivity of manganites in paramagnetic phase

The experimental results of studying the resistivity and magnetic susceptibility are presented for the single crystal La(1-x)Sr(x)MnO(3) (x=0.15;0.175) and CaMnO(3-d). We revealed the temperature dependence of the magnetic component of activation energy of hopping conductivity (Em) in paramagnetic phase: Em=Em0(+ or -)a/T, where the "+" sign corresponds to antiferromagnetic manganite CaMnO(3-d), and the "-" sign to ferromagnetic manganites La(1-x)Sr(x)MnO(3). It has been shown that for antiferromagnetic that temperature dependence of activation energy has a maximum coinciding with a maximum of magnetic susceptibility. For ferromagnetic sample La(0.85)Sr(0.15)MnO(3) the minimum of activation energy and maximum of magnetic susceptibility also coincide. The results obtained are explained on the basic of the model proposed in Gor'kov's works.