钙钛矿锰氧化物(La_(1-x)Eu_x)_(4/3)Sr_(5/3)Mn_2O_7(x=0,0.15)的磁性和电性研究

通过传统固相反应法制备了钙钛矿锰氧化物(La1-xEux)4/3Sr5/3Mn2O7(x=0,0.15)多晶样品,并且对其磁性和电性进行了研究.磁性测量表明:随着温度的降低,样品经历了一个复杂的转变过程,在温度为T*时经历二维短程铁磁有序转变,在温度为TC时进入三维长程铁磁态.随着Eu的掺杂,T*和TC减小,并且样品(La0.85Eu0.15)4/3Sr5/3Mn2O7在低温区表现出自旋玻璃行为.电性质测量表明:在母体La4/3Sr5/3Mn2O7中La位掺杂Eu后电阻率明显变大,金属绝缘转变温度TMI降低,磁电阻峰值增大.这些影响归因于较小的Eu3+离子替代La3+离子导致平均离子半径减小,晶格发生畸变.此外,较小的Eu3+离子优先占据层间岩盐层的R-site,使La3+,Sr3+,Eu3+离子在(La0.85Eu0.15)4/3Sr5/3Mn2O7中的分布更加有序,所以x=0.15的样品的ρ-T曲线只有一个峰.

Magnetic and transport properties of layered perovskite manganites (La1-xEu x)4/3Sr5/3Mn2O7(x=0, 0.15)

The samples (La_1-xEu_x)_4/3Sr_5/3Mn₂O₇ (x=0, 0.15) were prepared by the traditional solid-state reaction, and their magnetic and electrical properties were investigated. The magnetzation measurement reveals that as temperature lowers, all the samples undergo a complex magnetic transition process: they transform from the two-dimensional short-range ferromagnetic order at T^* into the three-dimensional long-range ferromagnetic state at T_C. With the increase of Eu doping, T^* and T_C are both reduced, and the sample (La_0.85Eu_0.15)_4/3Sr_5/3Mn₂O₇ exhibits spin-glass-like behaviour in a low temperature region. Electrical property measurements show that with the increase of Eu concentration, resistivity sharply increases, the metal-insulator transition temperature decreases and the magnetoresistance peak increases. These effects are attributed to the decrease of the average ionic radius diminution and the lattice distortion due to the substitution of the smaller Eu³⁺ ions for La³⁺ ions. In addition, the small-sized Eu³⁺ ion preferentially occupies the R site in the rock-salt layer, then the distributions of La³⁺, Sr³⁺, Eu³⁺ ions in the sample (La_0.85Eu_0.15)_4/3Sr_5/3Mn₂O₇ should be more orderly, so there is only one peak in the ρ-T curve of the sample with x=0.15.
Keywords： magnetic property electrical property magnetoresistance metal-insulator transition