Magnetic and transport properties of bilayered manganites La1.2Sr1.8Mn2-xGaxO7 （x =0, 0.08）

The magnetic and electrical properties of nonmagnetic Ga＋3 ion substitution for Mn site are investigated in the bilayer manganite La1.2Sr1.8Mn2-xGaxO7. When the Mn is substituted by Ga, the ferromagnetic property obviously weakens, the magnetic transition temperature decreases and a spin-glass behaviour occurs at low temperature. Meanwhile, doping causes the resistivity to dramatically increase, the metal-insulator transition temperature to disappear, and a greater magneto-resistance effect to occur at low temperature. These effects result from the fact that Ga substitution dilutes the magnetic active Mn-O-Mn network and weakens the double exchange interaction, and further suppresses ferromagnetic ordering and metallic conduction.