Magnetic and transport properties of bilayered perovskite manganites (La0.8Eu0.2)4/3Sr5/3Mn2O7

Abstract

Samples of (La0.8Eu0.2)4/3Sr5/3Mn2O7 were prepared by solid state reaction method. X-ray diffraction patterns indicated that the sample shows no any asymmetry and no any trace of secondary phase. The magnetization curve as a function of temperature (M-T), the magnetization versus magnetic field (M-H) at different temperatures, and the electron spin resonance spectrum have been detected. The magnetization measurement reveals that with lowing temperature, all of the samples undergo a complex magnetic transition. They transform from the two-dimensional short-range ferromagnetic order at TC2D ≈ 282 K, and enter the three-dimensional long-range ferromagnetic state at TC3D ≈ 259 K. Then they step into the antiferromagnetic state at TN ≈ 208 K and enter electric charge temperature order at TCO ≈ 35 K. The antimagnetic phase is found in the sample (La0.8Eu0.2)4/3Sr5/3Mn2O7below TN. When TC3D=370 K, the paramagnetic phase and antimagnetic phase co-exist. When TC3D is above 370 K, only paramagnetic phase exists in the sample. Besides, through electrical resistivity versus temperature curve ρ-T, the sample shows the maximum magnetization electrical resistivity when metal-insulator transition temperature is reached TP ≈ 80 K, TP being far from TC3D. And the transition shows the phenomenon of intrinsic magnetization electrical resistance, MR ≈ 61%. The resistance begins to increase below TCO. Because of the lowing temperature, the itinerant electron eg becomes increasingly spontaneously localized. One can see from the fitted ρ-T curves that (La0.8Eu0.2)4/3Sr5/3Mn2O7 in high temperature range is in accordance with the small polaron mode range hopping conduction.