| Mixed valance manganite with perovskite structure, with the divalent metal ions, has attracted much more attention. But alkali ion-substituted lanthanum manganites have been less studied. The effect of Fe doping (0≤y≤0.10) in B site and Na doping in A site was studied for the colossal La5/6Na1/6MnO3 magnetoresistance material. This is a search of new systems which is never reported until recent times. The samples were prepared by the sol-gel method for the first time. We report on the magnetic and transport measurements. We have focused on the effect of the addition Fe. Increased spin disorder and a decrease of with increasing Fe content are evident. It depopulates the hopping electrons and weakens the double exchange. From resistivity and magnetization data, it is expected that the addition of Fe can introduce grain boundaries and form antiferromagnetic clusters. The temperature dependence of resistivity shows that all samples undergo a transition accompanying a paramagnetic to ferromagnetic with the decrease of temperature. However, for y=0.10 sample, two obvious peaks are observed in the magnetoresistance versus temperature curve at 5 Tesla field. Grain surface expands with the increasing y and the conductivity channels reduce. The behavior of MR described may be attributed to the role of grain boundaries and the difference between the magnetization in the bulk and at the grain boundary surface. Hence the contributions to the resistivity of the internal tunneling become larger. The low field MR effect observed in the present Fe-doped samples seemd related to the second-order tunneling through interfacial spin sited at the grain boundary. The colossal magnetoresistance effect and the low-field magnetoresistance have been observed in this systems.The resistivity and TC...
|
PDF Full Text Request