Abstract:
La$_{0.7}$Sr$_{0.3}$Mn$_{0.9}$Cu$_{0.1}$O$_3$ ceramic samples have been obtained by the conventional method of the solid-phase reaction, and their resistivity $\rho$ has been investigated in a temperature range from 50 to 300 K in magnetic fields $B$ = 0–20 T. Dependences are typical of perovskite manganites with a maximum at $T_{\mathrm{max}}$ = 140–150 K and an increase in $\rho$ near $T_{\mathrm{max}}$ with increasing external magnetic field $B$. It has been established that the behavior of resistivity is caused by the variable range hopping conduction mechanism $\rho(T)=\rho_0(T)\exp[(T_0/T)^{1/4}]$, where $\rho_0(T)\sim T^{25/4}$. The Mott variable range hopping conduction has been observed below the Curie temperature for La$_{0.7}$Sr$_{0.3}$Mn$_{0.9}$Cu$_{0.1}$O$_3$ samples ($T_C\sim$ 300 K) in a temperature range from 300 to 200 K. The influence of Cu doping on the properties of La$_{0.7}$Sr$_{0.3}$MnO$_3$ samples is apparently caused by an additional distortion introduced into the crystal lattice of the material and by a weakening of the double-exchange mechanism.
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