Magnetoresistance of polycrystalline layered manganites La(sub 2-2x)Sr(sub 1+2x)Mn(sub 2)O(sub 7)

The magnetoresistance (MR) of polycrystalline layered manganites La(sub 2-2x)Sr(sub 1+2x)Mn(sub 2)O(sub 7) was investigated in doping levels of x=0.4 and 0.5. The samples were found to undergo a metal-insulator transition near a ferromagnetic ordering temperature that is linked with a large negative MR. The 40% doped samples exhibited a low-field MR that was similar to that grain-boundary MR of polycrystalline La(sub 0.7)Sr(sub 0.3)MnO(sub 3).