Magnetic and transport properties of bilayered manganites La_1.2Sr_1.8Mn_2-xGa_xO₇ (x=0, 0.08)^*

The magnetic and electrical properties of nonmagnetic Ga⁺³ ion substitution for Mn site are investigated in the bilayer manganite La_1.2Sr_1.8Mn₂O₇. 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.