Influence of Tb substitution for La on the structure, magnetic and magneto-transport properties of La1.2Sr1.8Mn2O7

The physical properties of Tb3+ ions substitution at A-site are investigated in the layered manganite La1.2Sr1.8Mn2O7. A series of La1.2−xTbxSr1.8Mn2O7 (x=0, 0.05, 0.15, and 0.20) shows that doping with a Tb ion of smaller radius in La1.2Sr1.8Mn2O7 caused diffraction peaks to shift to high angle. Some samples have an impure diffraction at about 30°, but all samples form single-phase. Samples can be well indexed on a Sr3Ti2O7-type tetragonal structure with the space group I4/mmm. According to the M-T curves, when x≤0.05, the series of samples shows ferromagnetism at low temperatures. With increasing temperature, they have two magnetic transitions at different temperatures. When x≥0.15, the magnetizations dramatically decrease. The ρ-T curves of samples show the metal-insulator transition for x=0, 0.05, and the maximum MR values in magnetic field 5 T are 74% at about 73 K and 94% at about 86 K. When x≥0.15, the samples remain in the insulator state in the whole observed temperature range, and the maximum MR values of 86% and 69% appeared at 74 K and 42 K.