| Abstract | The temperature T and magnetic-field H dependences of anisotropic in-plane rhoab and out-of-plane rhoc resistivities are investigated in single crystals of the bilayer manganite La1.2Sr1.8Mn2O7. Below the Curie transition temperature Tc=125 K, rhoab and rhoc display almost the same temperature dependence with an up-turn around 50 K. In the metallic regime (50 K <=T<= 110 K), both rhoab(T) and rhoc(T) follow a T9/2 dependence, consistent with the two-magnon scattering. We found that the value of the proportionality coefficient Bfitab and the ratio of the exchange interaction Jab/Jc, obtained by fitting the data, are in excellent agreement with the calculated Bab based on the two-magnon model and Jab/Jc deduced from neutron scattering, respectively. This provides further support for this scattering mechanism. At even lower T, in the nonmetallic regime (T<50 K), both the in-plane sigmaab and out-of-plane sigmac conductivities obey a T1/2 dependence, consistent with weak-localization effects. Hence this demonstrates the three-dimensional metallic nature of the bilayer manganite La1.2Sr1.8Mn2O7 at Tc. |
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