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VOLUME 69 (1999) | ISSUE 11 | PAGE 812
A sharp decrease of resistivity in La0.7Ca0.3Mn0.96Cu0.04O3: Evidence for Cu assisted coherent tunneling of spin polarons
PACS: 71.27.+a, 71.30.+h, 75.50.Cc
Nearly Á 50% decrease of resistivity p{T, χ) due to just 4% Cu doping on the Mn site of øÁ2/ÚóÁ1ÕÚíÐ1_Á.óÉÁ.ïÚ is observed. Attributing the observed phenomenon to the decrease of the spin-polaron energy E„(x) below Tc(x), all data are found to be well fitted by the nonthermal coherent tunneling expression p(T, x) = poe~',M <žτžχ^ assuming Eq.(2) for the magnetization in the ferromagnetic state. The best fits through all the data points suggest M0(x) ~ νΤ^ϊΛίο(Ο), íÌ(È) ~ ^/xMo(0), and Εσ(χ) ~ Εσ(0)(1 χ)4 for explicit χ dependence of the Cu induced modifications of the Mn spins dominated zero-temperature spontaneous magnetization, residual paramagnetic contribution, and spin-polaron tunneling energy, respectively, with Εσ(0) = 0.12eV.